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ip6tablesのヘルプ・マニュアル

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ip6tables --help

ip6tables v1.4.7 Usage: ip6tables -[ACD] chain rule-specification [options] ip6tables -I chain [rulenum] rule-specification [options] ip6tables -R chain rulenum rule-specification [options] ip6tables -D chain rulenum [options] ip6tables -[LS] [chain [rulenum]] [options] ip6tables -[FZ] [chain] [options] ip6tables -[NX] chain ip6tables -E old-chain-name new-chain-name ip6tables -P chain target [options] ip6tables -h (print this help information) Commands: Either long or short options are allowed. --append -A chain Append to chain --check -C chain Check for the existence of a rule --delete -D chain Delete matching rule from chain --delete -D chain rulenum Delete rule rulenum (1 = first) from chain --insert -I chain [rulenum] Insert in chain as rulenum (default 1=first) --replace -R chain rulenum Replace rule rulenum (1 = first) in chain --list -L [chain [rulenum]] List the rules in a chain or all chains --list-rules -S [chain [rulenum]] Print the rules in a chain or all chains --flush -F [chain] Delete all rules in chain or all chains --zero -Z [chain [rulenum]] Zero counters in chain or all chains --new -N chain Create a new user-defined chain --delete-chain -X [chain] Delete a user-defined chain --policy -P chain target Change policy on chain to target --rename-chain -E old-chain new-chain Change chain name, (moving any references) Options: [!] --proto -p proto protocol: by number or name, eg. `tcp' [!] --source -s address[/mask][,...] source specification [!] --destination -d address[/mask][,...] destination specification [!] --in-interface -i input name[+] network interface name ([+] for wildcard) --jump -j target target for rule (may load target extension) --goto -g chain jump to chain with no return --match -m match extended match (may load extension) --numeric -n numeric output of addresses and ports [!] --out-interface -o output name[+] network interface name ([+] for wildcard) --table -t table table to manipulate (default: `filter') --verbose -v verbose mode --line-numbers print line numbers when listing --exact -x expand numbers (display exact values) --modprobe= try to insert modules using this command --set-counters PKTS BYTES set the counter during insert/append [!] --version -V print package version.

ip6tables v1.4.7 Usage: ip6tables -[ACD] chain rule-specification [options] ip6tables -I chain [rulenum] rule-specification [options] ip6tables -R chain rulenum rule-specification [options] ip6tables -D chain rulenum [options] ip6tables -[LS] [chain [rulenum]] [options] ip6tables -[FZ] [chain] [options] ip6tables -[NX] chain ip6tables -E old-chain-name new-chain-name ip6tables -P chain target [options] ip6tables -h (print this help information) Commands: Either long or short options are allowed. --append -A chain Append to chain --check -C chain Check for the existence of a rule --delete -D chain Delete matching rule from chain --delete -D chain rulenum Delete rule rulenum (1 = first) from chain --insert -I chain [rulenum] Insert in chain as rulenum (default 1=first) --replace -R chain rulenum Replace rule rulenum (1 = first) in chain --list -L [chain [rulenum]] List the rules in a chain or all chains --list-rules -S [chain [rulenum]] Print the rules in a chain or all chains --flush -F [chain] Delete all rules in chain or all chains --zero -Z [chain [rulenum]] Zero counters in chain or all chains --new -N chain Create a new user-defined chain --delete-chain -X [chain] Delete a user-defined chain --policy -P chain target Change policy on chain to target --rename-chain -E old-chain new-chain Change chain name, (moving any references) Options: [!] --proto -p proto protocol: by number or name, eg. `tcp' [!] --source -s address[/mask][,...] source specification [!] --destination -d address[/mask][,...] destination specification [!] --in-interface -i input name[+] network interface name ([+] for wildcard) --jump -j target target for rule (may load target extension) --goto -g chain jump to chain with no return --match -m match extended match (may load extension) --numeric -n numeric output of addresses and ports [!] --out-interface -o output name[+] network interface name ([+] for wildcard) --table -t table table to manipulate (default: `filter') --verbose -v verbose mode --line-numbers print line numbers when listing --exact -x expand numbers (display exact values) --modprobe= try to insert modules using this command --set-counters PKTS BYTES set the counter during insert/append [!] --version -V print package version.

man ip6tables

IP6TABLES(8) IP6TABLES(8) 名前 ip6tables - IPv6 パケットフィルタを管理する 書式 ip6tables [-t テーブル] -[AD] チェイン ルールの詳細 [オプション] ip6tables [-t テーブル] -I チェイン [ルール番号] ルールの詳細 [オプショ ン] ip6tables [-t テーブル] -R チェイン ルール番号 ルールの詳細 [オプ シ ョ ン] ip6tables [-t テーブル] -D チェイン ルール番号 [オプション] ip6tables [-t テーブル] -[LFZ] [チェイン] [オプション] ip6tables [-t テーブル] -N チェイン ip6tables [-t テーブル] -X [チェイン] ip6tables [-t テーブル] -P チェイン ターゲット [オプション] ip6tables [-t テーブル] -E 旧チェイン名 新チェイン名 説明 ip6tables は Linux カーネルの IPv6 パケットフィルタルールのテーブルを設 定・管理・検査するために使われる。複数の異なるテーブルが定義される可 能 性 がある。各テーブルは組み込み済みチェインを含む。さらにユーザー定義の チェインを含むこともできる。 各チェインは、パケット群にマッチするルールのリストである。各ルールは マ ッ チしたパケットに対して何をするかを指定する。これは「ターゲット」と呼 ばれ、同じテーブル内のユーザー定義チェインにジャンプすることもある。 ターゲット ファイアウォールのルールは、パケットを判断する基準とターゲットを指定 す る 。パケットがマッチしない場合、チェイン内の次のルールが評価される。パ ケットがマッチした場合、ターゲットの値によって次のルールが指定される 。 タ ー ゲ ットの値は、ユーザー定義チェインの名前、または特別な値 ACCEPT, DROP, QUEUE, RETURN のうちの 1 つである。 ACCEPT はパケットを通すという意味である。 DROP はパケットを床に落す (捨 てる) という意味である。 QUEUE はパケットをユーザー空間に渡すという意味 である (カーネルがサポートしていればであるが)。 RETURN は、このチェイン を 検討することを中止して、前の (呼び出し側) チェインの次のルールで停止 するという意味である。組み込み済みチェインの最後に到達した場合、また は タ ーゲット RETURN が含まれている組み込み済みチェインのルールにマッチし た場合、チェインポリシーで指定されたターゲットがパケットの行方を決定 す る。 テーブル 現在のところ 2 つの独立なテーブルが存在する (どのテーブルがどの時点で現 れるかは、カーネルの設定やどういったモジュールが存在するかに依存する)。 nat テーブルは、まだ実装されていない。 -t, --table table このオプションは、どのコマンドを適用すべきかを決定するためのパケ ットマッチングテーブルを指定する。カーネルに自動モジュールローデ ィングが設定されている場合、あるテーブルに対して適切なモジュール がまだロードされていなければ、そのモジュールのロードを行う。 テーブルは以下の通りである。 filter: (-t オプションが指定されていない場合は) これがデフォルトのテ ーブルである。これには INPUT (マシン自体に入ってくるパケット に対するチェイン)・ FORWARD (マシンを経由するパケットに対 す るチェイン)・ OUTPUT (ローカルマシンで生成されたパケットに対 するチェイン) という組み込み済みチェインが含まれる。 mangle: このテーブルは特別なパケット変換に使われる。カーネル 2.4.17 ま では、 PREROUTING (パケットが入ってきた場合、すぐにそのパ ケットを変換するためのチェイン)・ OUTPUT (ローカルで生成され たパケットをルーティングの前に変換するためのチェイン) という 2 つの組み込み済みチェインが含まれていた。カーネル 2.4.18 か らは、これらの他に INPUT (マシン自体に入ってくるパケットに対 するチェイン)・ FORWARD (マシンを経由するパケットに対する チ ェ イン)・ POSTROUTING (パケットが出て行くときに変換するため のチェイン)・という 3 つの組み込み済みチェインもサポートされ る。 オプション ip6tables で使えるオプションは、いくつかのグループに分けられる。 コマンド こ れらのオプションは、実行する特定の動作を指定する。以下の説明で許可さ れていない限り、この中の 1 つしかコマンドラインで指定することができない 。長いバージョンのコマンド名とオプション名は、 ip6tables が他のコマンド 名やオプション名と区別できる範囲で (文字を省略して) 指定することもで き る。 -A, --append chain rule-specification 選 択されたチェインの最後に 1 つ以上のルールを追加する。送信元や 送信先の名前が 1 つ以上のアドレスに対応している場合、可能なア ド レスの組合せのそれぞれについてルールが追加される。 -D, --delete chain rule-specification -D, --delete chain rulenum 選 択されたチェインから 1 つ以上のルールを削除する。このコマンド には 2 つの使い方がある: チェインの中の番号 (最初のルールを 1 と する) を指定する場合と、マッチするルールを指定する場合である。 -I, --insert 選 択されたチェインにルール番号を指定して 1 つ以上のルールを挿入 する。ルール番号が 1 の場合、ルールはチェインの先頭に挿入され る 。これはルール番号が指定されない場合のデフォルトでもある。 -R, --replace chain rulenum rule-specification 選択されたチェインにあるルールを置き換える。送信元や送信先の名前 が 1 つ以上のアドレスに対応している場合は失敗する。ルールには 1 から始まる番号が付けられている。 -L, --list [chain] 選択されたチェインにある全てのルールを一覧表示する。チェインが指 定されない場合、全てのチェインにあるリストが一覧表示される。他の 各 iptables コマンドと同様に、指定されたテーブル (デフォルトは filter) に対して作用する。よって mangle ルールを表示するには以下 のようにする。 ip6tables -t mangle -n -L DNS の逆引きを避けるために、よく -n オプションと共に使用される。 -Z (ゼロ化) オプションを同時に指定することもできる。この場合、チ ェインは要素毎にリストされて、 (訳註: パケットカウンタとバイトカ ウンタが) ゼロにされる。どのように出力するかは、与えられる他の引 き数に影響される。 ip6tables -L -v を使わない限り、(訳註: -v オプションを指定しない限り) 実際のルー ルそのものは表示されない。 -F, --flush [chain] 選択されたチェイン (何も指定されなければテーブル内の全てのチェイ ン) の内容を全消去する。これは全てのルールを 1 個ずつ削除するの と同じである。 -Z, --zero [chain] すべてのチェインのパケットカウンタとバイトカウンタをゼロにする。 ク リ アされる直前のカウンタを見るために、 -L, --list (一覧表示) オプションと同時に指定することもできる (上記を参照)。 -N, --new-chain chain 指定した名前でユーザー定義チェインを作成する。同じ名前のターゲッ トが既に存在してはならない。 -X, --delete-chain [chain] オプションのユーザー定義チェインを削除する。そのチェインが参照さ れていてはならない。チェインを削除する前に、そのチェインを参照し ているルールを削除するか置き換えるかしなければならない。引き数が 与えられない場合、テーブルにあるチェインのうち組み込み済みチェイ ンでないものを全て削除する。 -P, --policy chain target チェインのポリシーを、指定したターゲットに設定する。指定可能なタ ーゲットは「ターゲット」の章を参照すること。 (ユーザー定義ではな い) 組み込み済みチェインにしかポリシーは設定できない。また、組み 込み済みチェインもユーザー定義チェインもポリシーのターゲットに設 定することはできない。 -E, --rename-chain old-chain new-chain ユーザー定義チェインを指定した名前に変更する。これは見た目だけの 変更なので、テーブルの構造には何も影響しない。 -h ヘルプ。 (今のところはとても簡単な) コマンド書式の説明を表示する 。 パラメータ 以下のパラメータは (add, delete, insert, replace, append コマンドで用い られて) ルールの仕様を決める。 -p, --protocol [!] protocol ルールで使われるプロトコル、またはチェックされるパケットのプロト コ ル 。指定できるプロトコルは、 tcp, udp, ipv6-icmp|icmpv6, all のいずれか 1 つか、数値である。数値は、これらのプロトコルの 1 つ 、もしくは別のプロトコルを表す。 /etc/protocols にあるプロトコル 名も指定できる。プロトコルの前に "!" を置くと、そのプロトコル を 指 定 しないという意味になる。数値 0 は all と等しい。プロトコル all は全てのプロトコルとマッチし、このオプションが省略された際の デフォルトである。 -s, --source [!] address[/mask] 送 信元の指定。 address はホスト名 (DNS のようなリモートへの問い 合わせで解決する名前を指定するのは非常に良くない)・ネットワー ク IPv6 アドレス (/mask を指定する)・通常の IPv6 アドレス (今のとこ ろ、ネットワーク名はサポートされていない)、のいずれかで あ る 。 mask はネットワークマスクか、ネットワークマスクの左側にある 1 の 数を指定する数値であ る 。 つ ま り 、 64 と い う mask は ffff:ffff:ffff:ffff:0000:0000:0000:0000 に等しい。アドレス指定の 前に "!" を置くと、そのアドレスを除外するという意味になる。フ ラ グ --src は、このオプションの別名である。 -d, --destination [!] address[/mask] 送 信先の指定。書式の詳しい説明については、 -s (送信元) フラグの 説明を参照すること。フラグ --dst は、このオプションの別名であ る 。 -j, --jump target ルールのターゲット、つまり、パケットがマッチした場合にどうするか を指定する。ターゲットはユーザー定義チェイン (そのルール自身が入 っているチェイン以外) でも、パケットの行方を即時に決定する特別な 組み込み済みターゲットでも、拡張されたターゲット (以下の 「タ ー ゲットの拡張」を参照) でもよい。このオプションがルールの中で省略 された場合、ルールにマッチしてもパケットの行方に何も影響しないが 、ルールのカウンタは 1 つ加算される。 -i, --in-interface [!] name (INPUT, FORWARD, PREROUTING チェインのみに入る) パケットを受信す るインターフェース名。インターフェース名の前に "!" を置くと、 そ のインターフェースを除外するという意味になる。インターフェース名 が "+" で終っている場合、その名前で始まる任意のインターフェー ス 名にマッチする。このオプションが省略された場合、任意のインターフ ェース名にマッチする。 -o, --out-interface [!] name (FORWARD, OUTPUT チェインに入る) パケットを送信するインターフ ェ ー ス名。インターフェース名の前に "!" を置くと、そのインターフェ ースを除外するという意味になる。インターフェース名が "+" で終 っ ている場合、その名前で始まる任意のインターフェース名にマッチする 。このオプションが省略された場合、任意のインターフェース名にマッ チする。 -c, --set-counters PKTS BYTES こ のオプションを使うと、 (insert, append, replace 操作において) 管理者はパケットカウンタとバイトカウンタを初期化することができる 。 その他のオプション その他に以下のオプションを指定することができる: -v, --verbose 詳細な出力を行う。 list コマンドの際に、インターフェース名・ (も しあれば) ルールのオプション・TOS マスクを表示させる。パケットと バ イ ト カ ウ ンタも表示される。添字 ’K’, ’M’, ’G’ は、それぞれ 1000, 1,000,000, 1,000,000,000 倍を表す (これを変更する -x フ ラ グも見よ)。このオプションを append, insert, delete, replace コマ ンドに適用すると、ルールについての詳細な情報を表示する。 -n, --numeric 数値による出力を行う。 IP アドレスやポート番号を数値によるフォー マ ッ トで表示する。デフォルトでは、このプログラムは (可能であれ ば) これらの情報をホスト名・ネットワーク名・サービス名で表示しよ うとする。 -x, --exact 厳 密 な 数 値で表示する。パケットカウンタとバイトカウンタを、 K (1000 の何倍か)・M (1000K の何倍か)・G (1000M の何倍か) ではなく 、厳密な値で表示する。このオプションは、 -L コマンドとしか関係し ない。 --line-numbers ルールを一覧表示する際、そのルールがチェインのどの位置にあるかを 表す行番号を各行の始めに付加する。 --modprobe=command チェインにルールを追加または挿入する際に、 (ターゲットやマッチン グの拡張などで) 必要なモジュールをロードするために使 う command を指定する。 マッチングの拡張 ip6tables は拡張されたパケットマッチングモジュールを使うことができる。 これらのモジュールは 2 種類の方法でロードされる: モジュールは、 -p また は --protocol で暗黙のうちに指定されるか、 -m または --match の後にモジ ュール名を続けて指定される。これらのモジュールの後ろには、モジュール に 応 じて他のいろいろなコマンドラインオプションを指定することができる。複 数の拡張マッチングモジュールを 1 行で指定することができる。また、モジュ ー ルに特有のヘルプを表示させるためには、モジュールを指定した後で -h ま たは --help を指定すればよい。 以下の拡張がベースパッケージに含まれている。大部分のものは、マッチン グ の意味を逆にするために ! を前におくことができる。 tcp こ れらの拡張は ‘--protocol tcp’ が指定され場合にロードされ、以下のオプ ションが提供される: --source-port [!] port[:port] 送信元ポートまたはポート範囲の指定。サービス名またはポート番号を 指 定できる。 port:port という形式で、2 つの番号を含む範囲を指定 することもできる。最初のポートを省略した場合、"0" を仮定する。最 後のポートを省略した場合、"65535" を仮定する。最後のポートが最初 のポートより大きい場合、2 つは入れ換えられる。フラグ --sport は 、このオプションの便利な別名である。 --destination-port [!] port[:port] 送 信先ポートまたはポート範囲の指定。フラグ --dport は、このオプ ションの便利な別名である。 --tcp-flags [!] mask comp 指定されているような TCP フラグの場合にマッチする。第 1 引き数は 評 価されるフラグで、コンマで分けられたリストで書かれる。第 2 引 き数は設定されていなければならないフラグで、コンマで分けられたリ ス ト で書かれる。指定できるフラグは SYN ACK FIN RST URG PSH ALL NONE である。よって、コマンド ip6tables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN は、SYN フラグが設定され ACK, FIN, RST フラグが設定されていな い パケットにのみマッチする。 [!] --syn SYN ビットが設定され ACK と RST ビットがクリアされている TCP パ ケットにのみマッチする。このようなパケットは TCP 接続の開始要 求 に使われる。例えば、インターフェースに入ってくるこのようなパケッ トをブロックすれば、内側への TCP 接続は禁止されるが、外 側 へ の TCP 接続には影響しない。これは --tcp-flags SYN,RST,ACK SYN と等 しい。 "--syn" の前に "!" フラグを置くと、 SYN ビットがクリア さ れ ACK と FIN ビットが設定されている TCP パケットにのみマッチす る。 --tcp-option [!] number TCP オプションが設定されている場合にマッチする。 udp これらの拡張は ‘--protocol udp’ が指定された場合にロードされ、以下の オ プションが提供される: --source-port [!] port[:port] 送 信元ポートまたはポート範囲の指定。詳細は TCP 拡張の --source- port オプションの説明を参照すること。 --destination-port [!] port[:port] 送信先ポートまたはポート範囲の指定。詳細は TCP 拡張の --destina- tion-port オプションの説明を参照すること。 ipv6-icmp これらの拡張は ‘--protocol ipv6-icmp’ または ‘--protocol icmpv6’ が指定 された場合にロードされ、以下のオプションが提供される: --icmpv6-type [!] typename 数値の IPv6-ICMP タイプ、またはコマンド ip6tables -p ipv6-icmp -h で表示される IPv6-ICMP タイプ名を指定できる。 mac --mac-source [!] address 送信元 MAC アドレスにマッチする。 address は XX:XX:XX:XX:XX:XX という形式でなければならない。イーサーネットデバイスから入ってく るパケットで、 PREROUTING, FORWARD, INPUT チェインに入るパケット にしか意味がない点に注意すること。 limit こ のモジュールは、トークンバケツフィルタを使い、単位時間あたり制限され た回数だけマッチする。この拡張を使ったルールは、(‘!’ フラグが指定されな い 限り) 制限に達するまでマッチする。このモジュールは、ログ記録を制限す る LOG ターゲットと組み合わせて使うことができる。たとえば、 --limit rate 単位時間あたりの平均マッチ回数の最大値。数値で指定さ れ 、 添 字 ‘/second’, ‘/minute’, ‘/hour’, ‘/day’ を付けることもできる。デフ ォルトは 3/hour である。 --limit-burst number パケットがマッチする回数の最大初期値: 上のオプションで指定した制 限 に達しなければ、その度ごとに、この数値になるまで 1 個ずつ増や される。デフォルトは 5 である。 multiport このモジュールは送信元や送信先のポートの集合にマッチする。ポート は 15 個 まで指定できる。このモジュールは -p tcp または -p udp と組み合わせて 使うことしかできない。 --source-ports port[,port[,port...]] 送信元ポートが指定されたポートのうちのいずれかであればマッチする 。フラグ --sports は、このオプションの便利な別名である。 --destination-ports port[,port[,port...]] 送信先ポートが指定されたポートのうちのいずれかであればマッチする 。フラグ --dports は、このオプションの便利な別名である。 --ports port[,port[,port...]] 送信元と送信先ポートの両方が互いに等しいか、指定されたポートのう ちのいずれかであればマッチする。 mark このモジュールはパケットに関連づけられた netfilter の mark フィールドに マッチする (このフィールドは、以下の MARK ターゲットで設定される)。 --mark value[/mask] 指定された符号なし mark 値のパケットにマッチする (mask が指定 さ れると、比較の前に mask との論理積 (AND) がとられる)。 owner こ のモジュールは、ローカルで生成されたパケットに付いて、パケット生成者 のいろいろな特性とのマッチングをとる。これは OUTPUT チェインのみでし か 有効でない。また、(ICMP ping 応答のような) パケットは、所有者がいないの で絶対にマッチしない。これは実験的なものという扱いである。 --uid-owner userid 指定された実効ユーザー ID のプロセスによりパケットが生成されてい る場合にマッチする。 --gid-owner groupid 指定された実効グループ ID のプロセスによりパケットが生成されてい る場合にマッチする。 --pid-owner processid 指定されたプロセス ID のプロセスによりパケットが生成されている場 合にマッチする。 --sid-owner sessionid 指定されたセッショングループのプロセスによりパケットが生成されて いる場合にマッチする。 ターゲットの拡張 iptables は拡張ターゲットモジュールを使うことができる: 以下のものが、標 準的なディストリビューションに含まれている。 LOG マ ッチしたパケットをカーネルログに記録する。このオプションがルールに対 して設定されると、 Linux カーネルはマッチしたパケットについて の (IPv6 に おける大部分の IPv6 ヘッダフィールドのような) 何らかの情報をカーネル ログに表示する (カーネルログは dmesg または syslogd(8) で見ることができ る) 。これは「非終了タ ーゲット」である。すなわち、ルールの検討は、次の ルールへと継続される。よって、拒否するパケットをログ記録したければ、 同 じ マッチング判断基準を持つ 2 つのルールを使用し、最初のルールで LOG タ ーゲットを、次のルールで DROP (または REJECT) ターゲットを指定する。 --log-level level ログ記録のレベル (数値で指定するか、 (訳註: 名前で指定する 場 合 は) syslog.conf(5) を参照すること)。 --log-prefix prefix 指定したプレフィックスをログメッセージの前に付ける。プレフィック スは 29 文字までの長さで、ログのなかでメッセージを区別するのに役 立つ。 --log-tcp-sequence TCP シーケンス番号をログに記録する。ログがユーザーから読める場合 、セキュリティ上の危険がある。 --log-tcp-options TCP パケットヘッダのオプションをログに記録する。 --log-ip-options IPv6 パケットヘッダのオプションをログに記録する。 MARK パケットに関連づけられた netfilter の mark 値を指定する。 mangle テーブ ルのみで有効である。 --set-mark mark REJECT マ ッチしたパケットの応答としてエラーパケットを送信するために使われる。 エラーパケットを送らなければ、 DROP と同じであり、 TARGET を終了し、 ル ー ルの検討を終了する。このターゲットは、 INPUT, FORWARD, OUTPUT チェイ ンと、これらのチェインから呼ばれるユーザー定義チェインだけで有効であ る 。以下のオプションは、返されるエラーパケットの特性を制御する。 --reject-with type type として指定可能なものは icmp6-no-route no-route icmp6-adm-prohibited adm-prohibited icmp6-addr-unreachable addr-unreach icmp6-port-unreachable port-unreach であり、適切な IPv6-ICMP エラーメッセージを返す (port-unreach が デフォルトである)。さらに、TCP プロトコルにのみマッチするルー ル に 対して、オプション tcp-reset を使うことができる。このオプショ ンを使うと、TCP RST パケットが送り返される 。 主 と し て ident (113/tcp) による探査を阻止するのに役立つ。 ident による探査は、 壊れている (メールを受け取らない) メールホストにメールが送られる 場合に頻繁に起こる。 返り値 い ろいろなエラーメッセージが標準エラーに表示される。正しく機能した場合 、終了コードは 0 である。不正なコマンドラインパラメータによりエラーが発 生した場合は、終了コード 2 が返される。その他のエラーの場合は、終了コー ド 1 が返される。 バグ バグ? バグって何? ;-) えーと…、sparc64 ではカウンター値が信頼できな い 。 IPCHAINS との互換性 ip6tables は、Rusty Russell の ipchains と非常によく似ている。大きな違 いは、チェイン INPUT と OUTPUT が、それぞれローカルホストに入ってくるパ ケ ットと、ローカルホストから出されるパケットのみしか調べないという点で ある。よって、全てのパケットは 3 つあるチェインのうち 1 つしか通らな い ( ル ープバックトラフィックは例外で、INPUT と OUTPUT チェインの両方を通 る)。以前は (ipchains では)、フォワードされるパケットが 3 つのチェイ ン 全てを通っていた。 そ の他の大きな違いは、 -i で入力インターフェース、 -o で出力インターフ ェースを指定し、ともに FORWARD チェインに入るパケットに対して指定可能な 点である。 ip6tables では、その他にもいくつかの変更がある。 関連項目 ip6tables-save(8), ip6tables-restore(8), iptables(8), iptables-save(8), iptables-restore(8). パケットフィルタリングについての詳細な iptables の使用法を説明してい る packet-filtering-HOWTO。 NAT について詳細に説明している NAT-HOWTO。標準 的 な 配 布 に は 含 ま れ な い 拡 張 の 詳 細 を 説 明 し て い る netfilter-extensions-HOWTO 。 内 部 構 造 に つ い て詳細に説明している netfilter-hacking-HOWTO。 http://www.netfilter.org/ を参照のこと。 著者 Rusty Russell は、初期の段階で Michael Neuling に相談して iptables を書 いた。 Marc Boucher は Rusty に iptables の一般的なパケット選択の考え方を勧め て、 ipnatctl を止めさせた。そして、mangle テーブル・所有者マッチング・ mark 機能を書き、いたるところで使われている素晴らしいコードを書いた。 James Morris が TOS ターゲットと tos マッチングを書いた。 Jozsef Kadlecsik が REJECT ターゲットを書いた。 Harald Welte が ULOG ターゲット・TTL マッチングと TTL ターゲット・ libipulog を書いた。 Netfilter コアチームは、Marc Boucher, Martin Josefsson, Jozsef Kadlec- sik, James Morris, Harald Welte, Rusty Russell である。 ip6tables の man ページは、Andras Kis-Szabo によって作成された。これは Herve Eychenne によって書かれた iptables の man ペ ー ジを元にしている。 Mar 09, 2002 IP6TABLES(8)

IP6TABLES(8) iptables 1.4.4 IP6TABLES(8) NAME ip6tables — IPv6 packet filter administration SYNOPSIS ip6tables [-t table] {-A|-C|-D} chain rule-specification [options...] ip6tables [-t table] -I chain [rulenum] rule-specification [options...] ip6tables [-t table] -R chain rulenum rule-specification [options...] ip6tables [-t table] -D chain rulenum [options...] ip6tables [-t table] -S [chain [rulenum]] ip6tables [-t table] {-F|-L|-Z} [chain [rulenum]] [options...] ip6tables [-t table] -N chain ip6tables [-t table] -X [chain] ip6tables [-t table] -P chain target [options...] ip6tables [-t table] -E old-chain-name new-chain-name DESCRIPTION Ip6tables is used to set up, maintain, and inspect the tables of IPv6 packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user-defined chains. Each chain is a list of rules which can match a set of packets. Each rule specifies what to do with a packet that matches. This is called a ‘target’, which may be a jump to a user-defined chain in the same ta- ble. TARGETS A firewall rule specifies criteria for a packet and a target. If the packet does not match, the next rule in the chain is the examined; if it does match, then the next rule is specified by the value of the tar- get, which can be the name of a user-defined chain or one of the spe- cial values ACCEPT, DROP, QUEUE or RETURN. ACCEPT means to let the packet through. DROP means to drop the packet on the floor. QUEUE means to pass the packet to userspace. (How the packet can be received by a userspace process differs by the particular queue handler. 2.4.x and 2.6.x kernels up to 2.6.13 include the ip_queue queue handler. Kernels 2.6.14 and later additionally include the nfnetlink_queue queue handler. Packets with a target of QUEUE will be sent to queue number ’0’ in this case. Please also see the NFQUEUE target as described later in this man page.) RETURN means stop traversing this chain and resume at the next rule in the previous (calling) chain. If the end of a built-in chain is reached or a rule in a built-in chain with target RETURN is matched, the target specified by the chain policy determines the fate of the packet. TABLES There are currently three independent tables (which tables are present at any time depends on the kernel configuration options and which mod- ules are present). -t, --table table This option specifies the packet matching table which the com- mand should operate on. If the kernel is configured with automatic module loading, an attempt will be made to load the appropriate module for that table if it is not already there. The tables are as follows: filter: This is the default table (if no -t option is passed). It contains the built-in chains INPUT (for packets destined to local sockets), FORWARD (for packets being routed through the box), and OUTPUT (for locally-generated packets). mangle: This table is used for specialized packet alteration. Until kernel 2.4.17 it had two built-in chains: PREROUTING (for altering incoming packets before routing) and OUTPUT (for altering locally-generated packets before routing). Since kernel 2.4.18, three other built-in chains are also sup- ported: INPUT (for packets coming into the box itself), FOR- WARD (for altering packets being routed through the box), and POSTROUTING (for altering packets as they are about to go out). raw: This table is used mainly for configuring exemptions from connection tracking in combination with the NOTRACK target. It registers at the netfilter hooks with higher priority and is thus called before ip_conntrack, or any other IP tables. It provides the following built-in chains: PREROUTING (for packets arriving via any network interface) OUTPUT (for packets generated by local processes) OPTIONS The options that are recognized by ip6tables can be divided into sev- eral different groups. COMMANDS These options specify the specific action to perform. Only one of them can be specified on the command line unless otherwise specified below. For all the long versions of the command and option names, you need to use only enough letters to ensure that ip6tables can differentiate it from all other options. -A, --append chain rule-specification Append one or more rules to the end of the selected chain. When the source and/or destination names resolve to more than one address, a rule will be added for each possible address combina- tion. -C, --check chain rule-specification Check whether a rule matching the specification does exist in the selected chain. This command uses the same logic as -D to find a matching entry, but does not alter the existing iptables configuration and uses its exit code to indicate success or failure. -D, --delete chain rule-specification -D, --delete chain rulenum Delete one or more rules from the selected chain. There are two versions of this command: the rule can be specified as a number in the chain (starting at 1 for the first rule) or a rule to match. -I, --insert chain [rulenum] rule-specification Insert one or more rules in the selected chain as the given rule number. So, if the rule number is 1, the rule or rules are inserted at the head of the chain. This is also the default if no rule number is specified. -R, --replace chain rulenum rule-specification Replace a rule in the selected chain. If the source and/or des- tination names resolve to multiple addresses, the command will fail. Rules are numbered starting at 1. -L, --list [chain] List all rules in the selected chain. If no chain is selected, all chains are listed. Like every other ip6tables command, it applies to the specified table (filter is the default). Please note that it is often used with the -n option, in order to avoid long reverse DNS lookups. It is legal to specify the -Z (zero) option as well, in which case the chain(s) will be atomically listed and zeroed. The exact output is affected by the other arguments given. The exact rules are suppressed until you use ip6tables -L -v -S, --list-rules [chain] Print all rules in the selected chain. If no chain is selected, all chains are printed like ip6tables-save. Like every other ip6tables command, it applies to the specified table (filter is the default). -F, --flush [chain] Flush the selected chain (all the chains in the table if none is given). This is equivalent to deleting all the rules one by one. -Z, --zero [chain [rulenum]] Zero the packet and byte counters in all chains, or only the given chain, or only the given rule in a chain. It is legal to specify the -L, --list (list) option as well, to see the coun- ters immediately before they are cleared. (See above.) -N, --new-chain chain Create a new user-defined chain by the given name. There must be no target of that name already. -X, --delete-chain [chain] Delete the optional user-defined chain specified. There must be no references to the chain. If there are, you must delete or replace the referring rules before the chain can be deleted. The chain must be empty, i.e. not contain any rules. If no argument is given, it will attempt to delete every non-builtin chain in the table. -P, --policy chain target Set the policy for the chain to the given target. See the sec- tion TARGETS for the legal targets. Only built-in (non-user- defined) chains can have policies, and neither built-in nor user-defined chains can be policy targets. -E, --rename-chain old-chain new-chain Rename the user specified chain to the user supplied name. This is cosmetic, and has no effect on the structure of the table. -A, --append chain rule-specification Append one or more rules to the end of the selected chain. When the source and/or destination names resolve to more than one address, a rule will be added for each possible address combina- tion. -h Help. Give a (currently very brief) description of the command syntax. PARAMETERS The following parameters make up a rule specification (as used in the add, delete, insert, replace and append commands). [!] -p, --protocol protocol The protocol of the rule or of the packet to check. The speci- fied protocol can be one of tcp, udp, udplite, icmpv6, esp, mh or all, or it can be a numeric value, representing one of these protocols or a different one. A protocol name from /etc/proto- cols is also allowed. But IPv6 extension headers except esp are not allowed. esp and ipv6-nonext can be used with Kernel ver- sion 2.6.11 or later. A "!" argument before the protocol inverts the test. The number zero is equivalent to all. Proto- col all will match with all protocols and is taken as default when this option is omitted. [!] -s, --source address[/mask] Source specification. Address can be either be a hostname, a network IP address (with /mask), or a plain IP address. Names will be resolved once only, before the rule is submitted to the kernel. Please note that specifying any name to be resolved with a remote query such as DNS is a really bad idea. (Resolv- ing network names is not supported at this time.) The mask is a plain number, specifying the number of 1’s at the left side of the network mask. A "!" argument before the address specifica- tion inverts the sense of the address. The flag --src is an alias for this option. Multiple addresses can be specified, but this will expand to multiple rules (when adding with -A), or will cause multiple rules to be deleted (with -D). [!] -d, --destination address[/mask] Destination specification. See the description of the -s (source) flag for a detailed description of the syntax. The flag --dst is an alias for this option. -j, --jump target This specifies the target of the rule; i.e., what to do if the packet matches it. The target can be a user-defined chain (other than the one this rule is in), one of the special builtin targets which decide the fate of the packet immediately, or an extension (see EXTENSIONS below). If this option is omitted in a rule (and -g is not used), then matching the rule will have no effect on the packet’s fate, but the counters on the rule will be incremented. -g, --goto chain This specifies that the processing should continue in a user specified chain. Unlike the --jump option return will not con- tinue processing in this chain but instead in the chain that called us via --jump. [!] -i, --in-interface name Name of an interface via which a packet was received (only for packets entering the INPUT, FORWARD and PREROUTING chains). When the "!" argument is used before the interface name, the sense is inverted. If the interface name ends in a "+", then any interface which begins with this name will match. If this option is omitted, any interface name will match. [!] -o, --out-interface name Name of an interface via which a packet is going to be sent (for packets entering the FORWARD, OUTPUT and POSTROUTING chains). When the "!" argument is used before the interface name, the sense is inverted. If the interface name ends in a "+", then any interface which begins with this name will match. If this option is omitted, any interface name will match. -c, --set-counters packets bytes This enables the administrator to initialize the packet and byte counters of a rule (during INSERT, APPEND, REPLACE operations). OTHER OPTIONS The following additional options can be specified: -v, --verbose Verbose output. This option makes the list command show the interface name, the rule options (if any), and the TOS masks. The packet and byte counters are also listed, with the suffix ’K’, ’M’ or ’G’ for 1000, 1,000,000 and 1,000,000,000 multipli- ers respectively (but see the -x flag to change this). For appending, insertion, deletion and replacement, this causes detailed information on the rule or rules to be printed. -n, --numeric Numeric output. IP addresses and port numbers will be printed in numeric format. By default, the program will try to display them as host names, network names, or services (whenever appli- cable). -x, --exact Expand numbers. Display the exact value of the packet and byte counters, instead of only the rounded number in K’s (multiples of 1000) M’s (multiples of 1000K) or G’s (multiples of 1000M). This option is only relevant for the -L command. --line-numbers When listing rules, add line numbers to the beginning of each rule, corresponding to that rule’s position in the chain. --modprobe=command When adding or inserting rules into a chain, use command to load any necessary modules (targets, match extensions, etc). MATCH EXTENSIONS ip6tables can use extended packet matching modules. These are loaded in two ways: implicitly, when -p or --protocol is specified, or with the -m or --match options, followed by the matching module name; after these, various extra command line options become available, depending on the specific module. You can specify multiple extended match mod- ules in one line, and you can use the -h or --help options after the module has been specified to receive help specific to that module. The following are included in the base package, and most of these can be preceded by a "!" to invert the sense of the match. ah This module matches the parameters in Authentication header of IPsec packets. [!] --ahspi spi[:spi] Matches SPI. [!] --ahlen length Total length of this header in octets. --ahres Matches if the reserved field is filled with zero. cluster Allows you to deploy gateway and back-end load-sharing clusters without the need of load-balancers. This match requires that all the nodes see the same packets. Thus, the cluster match decides if this node has to handle a packet given the following options: --cluster-total-nodes num Set number of total nodes in cluster. [!] --cluster-local-node num Set the local node number ID. [!] --cluster-local-nodemask mask Set the local node number ID mask. You can use this option instead of --cluster-local-node. --cluster-hash-seed value Set seed value of the Jenkins hash. Example: iptables -A PREROUTING -t mangle -i eth1 -m cluster --clus- ter-total-nodes 2 --cluster-local-node 1 --cluster-hash-seed 0xdeadbeef -j MARK --set-mark 0xffff iptables -A PREROUTING -t mangle -i eth2 -m cluster --clus- ter-total-nodes 2 --cluster-local-node 1 --cluster-hash-seed 0xdeadbeef -j MARK --set-mark 0xffff iptables -A PREROUTING -t mangle -i eth1 -m mark ! --mark 0xffff -j DROP iptables -A PREROUTING -t mangle -i eth2 -m mark ! --mark 0xffff -j DROP And the following commands to make all nodes see the same packets: ip maddr add 01:00:5e:00:01:01 dev eth1 ip maddr add 01:00:5e:00:01:02 dev eth2 arptables -A OUTPUT -o eth1 --h-length 6 -j mangle --mangle-mac- s 01:00:5e:00:01:01 arptables -A INPUT -i eth1 --h-length 6 --destination-mac 01:00:5e:00:01:01 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27 arptables -A OUTPUT -o eth2 --h-length 6 -j mangle --man- gle-mac-s 01:00:5e:00:01:02 arptables -A INPUT -i eth2 --h-length 6 --destination-mac 01:00:5e:00:01:02 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27 In the case of TCP connections, pickup facility has to be disabled to avoid marking TCP ACK packets coming in the reply direction as valid. echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose comment Allows you to add comments (up to 256 characters) to any rule. --comment comment Example: iptables -A INPUT -s 192.168.0.0/16 -m comment --comment "A pri- vatized IP block" connbytes Match by how many bytes or packets a connection (or one of the two flows constituting the connection) has transferred so far, or by aver- age bytes per packet. The counters are 64-bit and are thus not expected to overflow ;) The primary use is to detect long-lived downloads and mark them to be scheduled using a lower priority band in traffic control. The transferred bytes per connection can also be viewed through ‘con- ntrack -L‘ and accessed via ctnetlink. NOTE that for connections which have no accounting information, the match will always return false. The "net.netfilter.nf_conntrack_acct" sysctl flag controls whether new connections will be byte/packet counted. Existing connection flows will not be gaining/losing a/the accounting structure when be sysctl flag is flipped. [!] --connbytes from[:to] match packets from a connection whose packets/bytes/average packet size is more than FROM and less than TO bytes/packets. if TO is omitted only FROM check is done. "!" is used to match packets not falling in the range. --connbytes-dir {original|reply|both} which packets to consider --connbytes-mode {packets|bytes|avgpkt} whether to check the amount of packets, number of bytes trans- ferred or the average size (in bytes) of all packets received so far. Note that when "both" is used together with "avgpkt", and data is going (mainly) only in one direction (for example HTTP), the average packet size will be about half of the actual data packets. Example: iptables .. -m connbytes --connbytes 10000:100000 --connbytes-dir both --connbytes-mode bytes ... connlimit Allows you to restrict the number of parallel connections to a server per client IP address (or client address block). [!] --connlimit-above n Match if the number of existing connections is (not) above n. --connlimit-mask prefix_length Group hosts using the prefix length. For IPv4, this must be a number between (including) 0 and 32. For IPv6, between 0 and 128. Examples: # allow 2 telnet connections per client host iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-above 2 -j REJECT # you can also match the other way around: iptables -A INPUT -p tcp --syn --dport 23 -m connlimit ! --connlimit-above 2 -j ACCEPT # limit the number of parallel HTTP requests to 16 per class C sized network (24 bit netmask) iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16 --connlimit-mask 24 -j REJECT # limit the number of parallel HTTP requests to 16 for the link local network (ipv6) ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m connlimit --connlimit-above 16 --connlimit-mask 64 -j REJECT connmark This module matches the netfilter mark field associated with a connec- tion (which can be set using the CONNMARK target below). [!] --mark value[/mask] Matches packets in connections with the given mark value (if a mask is specified, this is logically ANDed with the mark before the comparison). conntrack This module, when combined with connection tracking, allows access to the connection tracking state for this packet/connection. [!] --ctstate statelist statelist is a comma separated list of the connection states to match. Possible states are listed below. [!] --ctproto l4proto Layer-4 protocol to match (by number or name) [!] --ctorigsrc address[/mask] [!] --ctorigdst address[/mask] [!] --ctreplsrc address[/mask] [!] --ctrepldst address[/mask] Match against original/reply source/destination address [!] --ctorigsrcport port [!] --ctorigdstport port [!] --ctreplsrcport port [!] --ctrepldstport port Match against original/reply source/destination port (TCP/UDP/etc.) or GRE key. [!] --ctstatus statelist statuslist is a comma separated list of the connection statuses to match. Possible statuses are listed below. [!] --ctexpire time[:time] Match remaining lifetime in seconds against given value or range of values (inclusive) --ctdir {ORIGINAL|REPLY} Match packets that are flowing in the specified direction. If this flag is not specified at all, matches packets in both directions. States for --ctstate: INVALID meaning that the packet is associated with no known connection NEW meaning that the packet has started a new connection, or other- wise associated with a connection which has not seen packets in both directions, and ESTABLISHED meaning that the packet is associated with a connection which has seen packets in both directions, RELATED meaning that the packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error. SNAT A virtual state, matching if the original source address differs from the reply destination. DNAT A virtual state, matching if the original destination differs from the reply source. Statuses for --ctstatus: NONE None of the below. EXPECTED This is an expected connection (i.e. a conntrack helper set it up) SEEN_REPLY Conntrack has seen packets in both directions. ASSURED Conntrack entry should never be early-expired. CONFIRMED Connection is confirmed: originating packet has left box. dccp [!] --source-port,--sport port[:port] [!] --destination-port,--dport port[:port] [!] --dccp-types mask Match when the DCCP packet type is one of ’mask’. ’mask’ is a comma-separated list of packet types. Packet types are: REQUEST RESPONSE DATA ACK DATAACK CLOSEREQ CLOSE RESET SYNC SYNCACK INVALID. [!] --dccp-option number Match if DCP option set. dscp This module matches the 6 bit DSCP field within the TOS field in the IP header. DSCP has superseded TOS within the IETF. [!] --dscp value Match against a numeric (decimal or hex) value [0-63]. [!] --dscp-class class Match the DiffServ class. This value may be any of the BE, EF, AFxx or CSx classes. It will then be converted into its accord- ing numeric value. dst This module matches the parameters in Destination Options header [!] --dst-len length Total length of this header in octets. --dst-opts type[:length][,type[:length]...] numeric type of option and the length of the option data in octets. esp This module matches the SPIs in ESP header of IPsec packets. [!] --espspi spi[:spi] eui64 This module matches the EUI-64 part of a stateless autoconfigured IPv6 address. It compares the EUI-64 derived from the source MAC address in Ethernet frame with the lower 64 bits of the IPv6 source address. But "Universal/Local" bit is not compared. This module doesn’t match other link layer frame, and is only valid in the PREROUTING, INPUT and FOR- WARD chains. frag This module matches the parameters in Fragment header. [!] --fragid id[:id] Matches the given Identification or range of it. [!] --fraglen length This option cannot be used with kernel version 2.6.10 or later. The length of Fragment header is static and this option doesn’t make sense. --fragres Matches if the reserved fields are filled with zero. --fragfirst Matches on the first fragment. --fragmore Matches if there are more fragments. --fraglast Matches if this is the last fragment. hashlimit hashlimit uses hash buckets to express a rate limiting match (like the limit match) for a group of connections using a single iptables rule. Grouping can be done per-hostgroup (source and/or destination address) and/or per-port. It gives you the ability to express "N packets per time quantum per group": matching on source host "1000 packets per second for every host in 192.168.0.0/16" matching on source prot "100 packets per second for every service of 192.168.1.1" matching on subnet "10000 packets per minute for every /28 subnet in 10.0.0.0/8" A hash limit option (--hashlimit-upto, --hashlimit-above) and --hash- limit-name are required. --hashlimit-upto amount[/second|/minute|/hour|/day] Match if the rate is below or equal to amount/quantum. It is specified as a number, with an optional time quantum suffix; the default is 3/hour. --hashlimit-above amount[/second|/minute|/hour|/day] Match if the rate is above amount/quantum. --hashlimit-burst amount Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5. --hashlimit-mode {srcip|srcport|dstip|dstport},... A comma-separated list of objects to take into consideration. If no --hashlimit-mode option is given, hashlimit acts like limit, but at the expensive of doing the hash housekeeping. --hashlimit-srcmask prefix When --hashlimit-mode srcip is used, all source addresses encountered will be grouped according to the given prefix length and the so-created subnet will be subject to hashlimit. prefix must be between (inclusive) 0 and 32. Note that --hashlimit-src- mask 0 is basically doing the same thing as not specifying srcip for --hashlimit-mode, but is technically more expensive. --hashlimit-dstmask prefix Like --hashlimit-srcmask, but for destination addresses. --hashlimit-name foo The name for the /proc/net/ipt_hashlimit/foo entry. --hashlimit-htable-size buckets The number of buckets of the hash table --hashlimit-htable-max entries Maximum entries in the hash. --hashlimit-htable-expire msec After how many milliseconds do hash entries expire. --hashlimit-htable-gcinterval msec How many milliseconds between garbage collection intervals. hbh This module matches the parameters in Hop-by-Hop Options header [!] --hbh-len length Total length of this header in octets. --hbh-opts type[:length][,type[:length]...] numeric type of option and the length of the option data in octets. helper This module matches packets related to a specific conntrack-helper. [!] --helper string Matches packets related to the specified conntrack-helper. string can be "ftp" for packets related to a ftp-session on default port. For other ports append -portnr to the value, ie. "ftp-2121". Same rules apply for other conntrack-helpers. hl This module matches the Hop Limit field in the IPv6 header. [!] --hl-eq value Matches if Hop Limit equals value. --hl-lt value Matches if Hop Limit is less than value. --hl-gt value Matches if Hop Limit is greater than value. icmp6 This extension can be used if ‘--protocol ipv6-icmp’ or ‘--protocol icmpv6’ is specified. It provides the following option: [!] --icmpv6-type type[/code]|typename This allows specification of the ICMPv6 type, which can be a numeric ICMPv6 type, type and code, or one of the ICMPv6 type names shown by the command ip6tables -p ipv6-icmp -h iprange This matches on a given arbitrary range of IP addresses. [!] --src-range from[-to] Match source IP in the specified range. [!] --dst-range from[-to] Match destination IP in the specified range. ipv6header This module matches IPv6 extension headers and/or upper layer header. --soft Matches if the packet includes any of the headers specified with --header. [!] --header header[,header...] Matches the packet which EXACTLY includes all specified headers. The headers encapsulated with ESP header are out of scope. Pos- sible header types can be: hop|hop-by-hop Hop-by-Hop Options header dst Destination Options header route Routing header frag Fragment header auth Authentication header esp Encapsulating Security Payload header none No Next header which matches 59 in the ’Next Header field’ of IPv6 header or any IPv6 extension headers proto which matches any upper layer protocol header. A protocol name from /etc/protocols and numeric value also allowed. The number 255 is equivalent to proto. length This module matches the length of the layer-3 payload (e.g. layer-4 packet) of a packet against a specific value or range of values. [!] --length length[:length] limit This module matches at a limited rate using a token bucket filter. A rule using this extension will match until this limit is reached (unless the ‘!’ flag is used). It can be used in combination with the LOG target to give limited logging, for example. --limit rate[/second|/minute|/hour|/day] Maximum average matching rate: specified as a number, with an optional ‘/second’, ‘/minute’, ‘/hour’, or ‘/day’ suffix; the default is 3/hour. --limit-burst number Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5. mac [!] --mac-source address Match source MAC address. It must be of the form XX:XX:XX:XX:XX:XX. Note that this only makes sense for packets coming from an Ethernet device and entering the PREROUTING, FOR- WARD or INPUT chains. mark This module matches the netfilter mark field associated with a packet (which can be set using the MARK target below). [!] --mark value[/mask] Matches packets with the given unsigned mark value (if a mask is specified, this is logically ANDed with the mask before the com- parison). mh This extension is loaded if ‘--protocol ipv6-mh’ or ‘--protocol mh’ is specified. It provides the following option: [!] --mh-type type[:type] This allows specification of the Mobility Header(MH) type, which can be a numeric MH type, type or one of the MH type names shown by the command ip6tables -p ipv6-mh -h multiport This module matches a set of source or destination ports. Up to 15 ports can be specified. A port range (port:port) counts as two ports. It can only be used in conjunction with -p tcp or -p udp. [!] --source-ports,--sports port[,port|,port:port]... Match if the source port is one of the given ports. The flag --sports is a convenient alias for this option. Multiple ports or port ranges are separated using a comma, and a port range is specified using a colon. 53,1024:65535 would therefore match ports 53 and all from 1024 through 65535. [!] --destination-ports,--dports port[,port|,port:port]... Match if the destination port is one of the given ports. The flag --dports is a convenient alias for this option. [!] --ports port[,port|,port:port]... Match if either the source or destination ports are equal to one of the given ports. owner This module attempts to match various characteristics of the packet creator, for locally generated packets. This match is only valid in the OUTPUT and POSTROUTING chains. Forwarded packets do not have any socket associated with them. Packets from kernel threads do have a socket, but usually no owner. [!] --uid-owner username [!] --uid-owner userid[-userid] Matches if the packet socket’s file structure (if it has one) is owned by the given user. You may also specify a numerical UID, or an UID range. [!] --gid-owner groupname [!] --gid-owner groupid[-groupid] Matches if the packet socket’s file structure is owned by the given group. You may also specify a numerical GID, or a GID range. [!] --socket-exists Matches if the packet is associated with a socket. physdev This module matches on the bridge port input and output devices enslaved to a bridge device. This module is a part of the infrastruc- ture that enables a transparent bridging IP firewall and is only useful for kernel versions above version 2.5.44. [!] --physdev-in name Name of a bridge port via which a packet is received (only for packets entering the INPUT, FORWARD and PREROUTING chains). If the interface name ends in a "+", then any interface which begins with this name will match. If the packet didn’t arrive through a bridge device, this packet won’t match this option, unless ’!’ is used. [!] --physdev-out name Name of a bridge port via which a packet is going to be sent (for packets entering the FORWARD, OUTPUT and POSTROUTING chains). If the interface name ends in a "+", then any inter- face which begins with this name will match. Note that in the nat and mangle OUTPUT chains one cannot match on the bridge out- put port, however one can in the filter OUTPUT chain. If the packet won’t leave by a bridge device or if it is yet unknown what the output device will be, then the packet won’t match this option, unless ’!’ is used. [!] --physdev-is-in Matches if the packet has entered through a bridge interface. [!] --physdev-is-out Matches if the packet will leave through a bridge interface. [!] --physdev-is-bridged Matches if the packet is being bridged and therefore is not being routed. This is only useful in the FORWARD and POSTROUT- ING chains. pkttype This module matches the link-layer packet type. [!] --pkt-type {unicast|broadcast|multicast} policy This modules matches the policy used by IPsec for handling a packet. --dir {in|out} Used to select whether to match the policy used for decapsula- tion or the policy that will be used for encapsulation. in is valid in the PREROUTING, INPUT and FORWARD chains, out is valid in the POSTROUTING, OUTPUT and FORWARD chains. --pol {none|ipsec} Matches if the packet is subject to IPsec processing. --strict Selects whether to match the exact policy or match if any rule of the policy matches the given policy. [!] --reqid id Matches the reqid of the policy rule. The reqid can be specified with setkey(8) using unique:id as level. [!] --spi spi Matches the SPI of the SA. [!] --proto {ah|esp|ipcomp} Matches the encapsulation protocol. [!] --mode {tunnel|transport} Matches the encapsulation mode. [!] --tunnel-src addr[/mask] Matches the source end-point address of a tunnel mode SA. Only valid with --mode tunnel. [!] --tunnel-dst addr[/mask] Matches the destination end-point address of a tunnel mode SA. Only valid with --mode tunnel. --next Start the next element in the policy specification. Can only be used with --strict. quota Implements network quotas by decrementing a byte counter with each packet. --quota bytes The quota in bytes. rateest The rate estimator can match on estimated rates as collected by the RATEEST target. It supports matching on absolute bps/pps values, com- paring two rate estimators and matching on the difference between two rate estimators. --rateest1 name Name of the first rate estimator. --rateest2 name Name of the second rate estimator (if difference is to be calcu- lated). --rateest-delta Compare difference(s) to given rate(s) --rateest1-bps value --rateest2-bps value Compare bytes per second. --rateest1-pps value --rateest2-pps value Compare packets per second. [!] --rateest-lt Match if rate is less than given rate/estimator. [!] --rateest-gt Match if rate is greater than given rate/estimator. [!] --rateest-eq Match if rate is equal to given rate/estimator. Example: This is what can be used to route outgoing data connections from an FTP server over two lines based on the available bandwidth at the time the data connection was started: # Estimate outgoing rates iptables -t mangle -A POSTROUTING -o eth0 -j RATEEST --rateest-name eth0 --rateest-interval 250ms --rateest-ewma 0.5s iptables -t mangle -A POSTROUTING -o ppp0 -j RATEEST --rateest-name ppp0 --rateest-interval 250ms --rateest-ewma 0.5s # Mark based on available bandwidth iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper --helper ftp -m rateest --rateest-delta --rateest1 eth0 --rateest-bps1 2.5mbit --rateest-gt --rateest2 ppp0 --rateest-bps2 2mbit -j CONNMARK --set-mark 1 iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper --helper ftp -m rateest --rateest-delta --rateest1 ppp0 --rateest-bps1 2mbit --rateest-gt --rateest2 eth0 --rateest-bps2 2.5mbit -j CONNMARK --set-mark 2 iptables -t mangle -A balance -j CONNMARK --restore-mark recent Allows you to dynamically create a list of IP addresses and then match against that list in a few different ways. For example, you can create a "badguy" list out of people attempting to connect to port 139 on your firewall and then DROP all future packets from them without considering them. --set, --rcheck, --update and --remove are mutually exclusive. --name name Specify the list to use for the commands. If no name is given then DEFAULT will be used. [!] --set This will add the source address of the packet to the list. If the source address is already in the list, this will update the existing entry. This will always return success (or failure if ! is passed in). --rsource Match/save the source address of each packet in the recent list table. This is the default. --rdest Match/save the destination address of each packet in the recent list table. [!] --rcheck Check if the source address of the packet is currently in the list. [!] --update Like --rcheck, except it will update the "last seen" timestamp if it matches. [!] --remove Check if the source address of the packet is currently in the list and if so that address will be removed from the list and the rule will return true. If the address is not found, false is returned. --seconds seconds This option must be used in conjunction with one of --rcheck or --update. When used, this will narrow the match to only happen when the address is in the list and was seen within the last given number of seconds. --hitcount hits This option must be used in conjunction with one of --rcheck or --update. When used, this will narrow the match to only happen when the address is in the list and packets had been received greater than or equal to the given value. This option may be used along with --seconds to create an even narrower match requiring a certain number of hits within a specific time frame. The maximum value for the hitcount parameter is given by the "ip_pkt_list_tot" parameter of the xt_recent kernel module. Exceeding this value on the command line will cause the rule to be rejected. --rttl This option may only be used in conjunction with one of --rcheck or --update. When used, this will narrow the match to only hap- pen when the address is in the list and the TTL of the current packet matches that of the packet which hit the --set rule. This may be useful if you have problems with people faking their source address in order to DoS you via this module by disallowing others access to your site by sending bogus packets to you. Examples: iptables -A FORWARD -m recent --name badguy --rcheck --seconds 60 -j DROP iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent --name badguy --set -j DROP Steve’s ipt_recent website (http://snowman.net/projects/ipt_recent/) also has some examples of usage. /proc/net/xt_recent/* are the current lists of addresses and informa- tion about each entry of each list. Each file in /proc/net/xt_recent/ can be read from to see the current list or written two using the following commands to modify the list: echo +addr >/proc/net/xt_recent/DEFAULT to add addr to the DEFAULT list echo -addr >/proc/net/xt_recent/DEFAULT to remove addr from the DEFAULT list echo / >/proc/net/xt_recent/DEFAULT to flush the DEFAULT list (remove all entries). The module itself accepts parameters, defaults shown: ip_list_tot=100 Number of addresses remembered per table. ip_pkt_list_tot=20 Number of packets per address remembered. ip_list_hash_size=0 Hash table size. 0 means to calculate it based on ip_list_tot, default: 512. ip_list_perms=0644 Permissions for /proc/net/xt_recent/* files. ip_list_uid=0 Numerical UID for ownership of /proc/net/xt_recent/* files. ip_list_gid=0 Numerical GID for ownership of /proc/net/xt_recent/* files. rt Match on IPv6 routing header [!] --rt-type type Match the type (numeric). [!] --rt-segsleft num[:num] Match the ‘segments left’ field (range). [!] --rt-len length Match the length of this header. --rt-0-res Match the reserved field, too (type=0) --rt-0-addrs addr[,addr...] Match type=0 addresses (list). --rt-0-not-strict List of type=0 addresses is not a strict list. sctp [!] --source-port,--sport port[:port] [!] --destination-port,--dport port[:port] [!] --chunk-types {all|any|only} chunktype[:flags] [...] The flag letter in upper case indicates that the flag is to match if set, in the lower case indicates to match if unset. Chunk types: DATA INIT INIT_ACK SACK HEARTBEAT HEARTBEAT_ACK ABORT SHUTDOWN SHUTDOWN_ACK ERROR COOKIE_ECHO COOKIE_ACK ECN_ECNE ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK chunk type available flags DATA U B E u b e ABORT T t SHUTDOWN_COMPLETE T t (lowercase means flag should be "off", uppercase means "on") Examples: iptables -A INPUT -p sctp --dport 80 -j DROP iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT set This module matches IP sets which can be defined by ipset(8). [!] --match-set setname flag[,flag]... where flags are the comma separated list of src and/or dst spec- ifications and there can be no more than six of them. Hence the command iptables -A FORWARD -m set --match-set test src,dst will match packets, for which (if the set type is ipportmap) the source address and destination port pair can be found in the specified set. If the set type of the specified set is single dimension (for example ipmap), then the command will match pack- ets for which the source address can be found in the specified set. The option --match-set can be replaced by --set if that does not clash with an option of other extensions. Use of -m set requires that ipset kernel support is provided. As stan- dard kernels do not ship this currently, the ipset or Xtables-addons package needs to be installed. socket This matches if an open socket can be found by doing a socket lookup on the packet. --transparent Ignore non-transparent sockets. state This module, when combined with connection tracking, allows access to the connection tracking state for this packet. [!] --state state Where state is a comma separated list of the connection states to match. Possible states are INVALID meaning that the packet could not be identified for some reason which includes running out of memory and ICMP errors which don’t correspond to any known connection, ESTABLISHED meaning that the packet is associ- ated with a connection which has seen packets in both direc- tions, NEW meaning that the packet has started a new connection, or otherwise associated with a connection which has not seen packets in both directions, and RELATED meaning that the packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error. statistic This module matches packets based on some statistic condition. It sup- ports two distinct modes settable with the --mode option. Supported options: --mode mode Set the matching mode of the matching rule, supported modes are random and nth. --probability p Set the probability from 0 to 1 for a packet to be randomly matched. It works only with the random mode. --every n Match one packet every nth packet. It works only with the nth mode (see also the --packet option). --packet p Set the initial counter value (0 <= p <= n-1, default 0) for the nth mode. string This modules matches a given string by using some pattern matching strategy. It requires a linux kernel >= 2.6.14. --algo {bm|kmp} Select the pattern matching strategy. (bm = Boyer-Moore, kmp = Knuth-Pratt-Morris) --from offset Set the offset from which it starts looking for any matching. If not passed, default is 0. --to offset Set the offset from which it starts looking for any matching. If not passed, default is the packet size. [!] --string pattern Matches the given pattern. [!] --hex-string pattern Matches the given pattern in hex notation. tcp These extensions can be used if ‘--protocol tcp’ is specified. It pro- vides the following options: [!] --source-port,--sport port[:port] Source port or port range specification. This can either be a service name or a port number. An inclusive range can also be specified, using the format first:last. If the first port is omitted, "0" is assumed; if the last is omitted, "65535" is assumed. If the first port is greater than the second one they will be swapped. The flag --sport is a convenient alias for this option. [!] --destination-port,--dport port[:port] Destination port or port range specification. The flag --dport is a convenient alias for this option. [!] --tcp-flags mask comp Match when the TCP flags are as specified. The first argument mask is the flags which we should examine, written as a comma- separated list, and the second argument comp is a comma-sepa- rated list of flags which must be set. Flags are: SYN ACK FIN RST URG PSH ALL NONE. Hence the command iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN will only match packets with the SYN flag set, and the ACK, FIN and RST flags unset. [!] --syn Only match TCP packets with the SYN bit set and the ACK,RST and FIN bits cleared. Such packets are used to request TCP connec- tion initiation; for example, blocking such packets coming in an interface will prevent incoming TCP connections, but outgoing TCP connections will be unaffected. It is equivalent to --tcp-flags SYN,RST,ACK,FIN SYN. If the "!" flag precedes the "--syn", the sense of the option is inverted. [!] --tcp-option number Match if TCP option set. tcpmss This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time. [!] --mss value[:value] Match a given TCP MSS value or range. time This matches if the packet arrival time/date is within a given range. All options are optional, but are ANDed when specified. --datestart YYYY[-MM[-DD[Thh[:mm[:ss]]]]] --datestop YYYY[-MM[-DD[Thh[:mm[:ss]]]]] Only match during the given time, which must be in ISO 8601 "T" notation. The possible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07. If --datestart or --datestop are not specified, it will default to 1970-01-01 and 2038-01-19, respectively. --timestart hh:mm[:ss] --timestop hh:mm[:ss] Only match during the given daytime. The possible time range is 00:00:00 to 23:59:59. Leading zeroes are allowed (e.g. "06:03") and correctly interpreted as base-10. [!] --monthdays day[,day...] Only match on the given days of the month. Possible values are 1 to 31. Note that specifying 31 will of course not match on months which do not have a 31st day; the same goes for 28- or 29-day February. [!] --weekdays day[,day...] Only match on the given weekdays. Possible values are Mon, Tue, Wed, Thu, Fri, Sat, Sun, or values from 1 to 7, respectively. You may also use two-character variants (Mo, Tu, etc.). --utc Interpret the times given for --datestart, --datestop, --times- tart and --timestop to be UTC. --localtz Interpret the times given for --datestart, --datestop, --times- tart and --timestop to be local kernel time. (Default) EXAMPLES. To match on weekends, use: -m time --weekdays Sa,Su Or, to match (once) on a national holiday block: -m time --datestart 2007-12-24 --datestop 2007-12-27 Since the stop time is actually inclusive, you would need the following stop time to not match the first second of the new day: -m time --datestart 2007-01-01T17:00 --datestop 2007-01-01T23:59:59 During lunch hour: -m time --timestart 12:30 --timestop 13:30 The fourth Friday in the month: -m time --weekdays Fr --monthdays 22,23,24,25,26,27,28 (Note that this exploits a certain mathematical property. It is not possible to say "fourth Thursday OR fourth Friday" in one rule. It is possible with multiple rules, though.) tos This module matches the 8-bit Type of Service field in the IPv4 header (i.e. including the "Precedence" bits) or the (also 8-bit) Priority field in the IPv6 header. [!] --tos value[/mask] Matches packets with the given TOS mark value. If a mask is specified, it is logically ANDed with the TOS mark before the comparison. [!] --tos symbol You can specify a symbolic name when using the tos match for IPv4. The list of recognized TOS names can be obtained by call- ing iptables with -m tos -h. Note that this implies a mask of 0x3F, i.e. all but the ECN bits. u32 U32 tests whether quantities of up to 4 bytes extracted from a packet have specified values. The specification of what to extract is general enough to find data at given offsets from tcp headers or payloads. [!] --u32 tests The argument amounts to a program in a small language described below. tests := location "=" value | tests "&&" location "=" value value := range | value "," range range := number | number ":" number a single number, n, is interpreted the same as n:n. n:m is interpreted as the range of numbers >=n and <=m. location := number | location operator number operator := "&" | "<<" | ">>" | "@" The operators &, <<, >> and && mean the same as in C. The = is really a set membership operator and the value syntax describes a set. The @ operator is what allows moving to the next header and is described fur- ther below. There are currently some artificial implementation limits on the size of the tests: * no more than 10 of "=" (and 9 "&&"s) in the u32 argument * no more than 10 ranges (and 9 commas) per value * no more than 10 numbers (and 9 operators) per location To describe the meaning of location, imagine the following machine that interprets it. There are three registers: A is of type char *, initially the address of the IP header B and C are unsigned 32 bit integers, initially zero The instructions are: number B = number; C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) + *(A+B+3) &number C = C & number << number C = C << number >> number C = C >> number @number A = A + C; then do the instruction number Any access of memory outside [skb->data,skb->end] causes the match to fail. Otherwise the result of the computation is the final value of C. Whitespace is allowed but not required in the tests. However, the char- acters that do occur there are likely to require shell quoting, so it is a good idea to enclose the arguments in quotes. Example: match IP packets with total length >= 256 The IP header contains a total length field in bytes 2-3. --u32 "0 & 0xFFFF = 0x100:0xFFFF" read bytes 0-3 AND that with 0xFFFF (giving bytes 2-3), and test whether that is in the range [0x100:0xFFFF] Example: (more realistic, hence more complicated) match ICMP packets with icmp type 0 First test that it is an ICMP packet, true iff byte 9 (protocol) = 1 --u32 "6 & 0xFF = 1 && ... read bytes 6-9, use & to throw away bytes 6-8 and compare the result to 1. Next test that it is not a fragment. (If so, it might be part of such a packet but we cannot always tell.) N.B.: This test is generally needed if you want to match anything beyond the IP header. The last 6 bits of byte 6 and all of byte 7 are 0 iff this is a complete packet (not a fragment). Alterna- tively, you can allow first fragments by only testing the last 5 bits of byte 6. ... 4 & 0x3FFF = 0 && ... Last test: the first byte past the IP header (the type) is 0. This is where we have to use the @syntax. The length of the IP header (IHL) in 32 bit words is stored in the right half of byte 0 of the IP header itself. ... 0 >> 22 & 0x3C @ 0 >> 24 = 0" The first 0 means read bytes 0-3, >>22 means shift that 22 bits to the right. Shifting 24 bits would give the first byte, so only 22 bits is four times that plus a few more bits. &3C then eliminates the two extra bits on the right and the first four bits of the first byte. For instance, if IHL=5, then the IP header is 20 (4 x 5) bytes long. In this case, bytes 0-1 are (in binary) xxxx0101 yyzzzzzz, >>22 gives the 10 bit value xxxx0101yy and &3C gives 010100. @ means to use this number as a new offset into the packet, and read four bytes starting from there. This is the first 4 bytes of the ICMP payload, of which byte 0 is the ICMP type. Therefore, we simply shift the value 24 to the right to throw out all but the first byte and compare the result with 0. Example: TCP payload bytes 8-12 is any of 1, 2, 5 or 8 First we test that the packet is a tcp packet (similar to ICMP). --u32 "6 & 0xFF = 6 && ... Next, test that it is not a fragment (same as above). ... 0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8" 0>>22&3C as above computes the number of bytes in the IP header. @ makes this the new offset into the packet, which is the start of the TCP header. The length of the TCP header (again in 32 bit words) is the left half of byte 12 of the TCP header. The 12>>26&3C computes this length in bytes (similar to the IP header before). "@" makes this the new offset, which is the start of the TCP payload. Finally, 8 reads bytes 8-12 of the payload and = checks whether the result is any of 1, 2, 5 or 8. udp These extensions can be used if ‘--protocol udp’ is specified. It pro- vides the following options: [!] --source-port,--sport port[:port] Source port or port range specification. See the description of the --source-port option of the TCP extension for details. [!] --destination-port,--dport port[:port] Destination port or port range specification. See the descrip- tion of the --destination-port option of the TCP extension for details. TARGET EXTENSIONS ip6tables can use extended target modules: the following are included in the standard distribution. AUDIT This target allows to create audit records for packets hitting the tar- get. It can be used to record accepted, dropped, and rejected packets. See auditd(8) for additional details. --type {accept|drop|reject} Set type of audit record. Example: iptables -N AUDIT_DROP iptables -A AUDIT_DROP -j AUDIT --type drop iptables -A AUDIT_DROP -j DROP CHECKSUM This target allows to selectively work around broken/old applications. It can only be used in the mangle table. --checksum-fill Compute and fill in the checksum in a packet that lacks a check- sum. This is particularly useful, if you need to work around old applications such as dhcp clients, that do not work well with checksum offloads, but don’t want to disable checksum offload in your device. CLASSIFY This module allows you to set the skb->priority value (and thus clas- sify the packet into a specific CBQ class). --set-class major:minor Set the major and minor class value. The values are always interpreted as hexadecimal even if no 0x prefix is given. CONNMARK This module sets the netfilter mark value associated with a connection. The mark is 32 bits wide. --set-xmark value[/mask] Zero out the bits given by mask and XOR value into the ctmark. --save-mark [--nfmask nfmask] [--ctmask ctmask] Copy the packet mark (nfmark) to the connection mark (ctmark) using the given masks. The new nfmark value is determined as follows: ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask) i.e. ctmask defines what bits to clear and nfmask what bits of the nfmark to XOR into the ctmark. ctmask and nfmask default to 0xFFFFFFFF. --restore-mark [--nfmask nfmask] [--ctmask ctmask] Copy the connection mark (ctmark) to the packet mark (nfmark) using the given masks. The new ctmark value is determined as follows: nfmark = (nfmark & ~nfmask) ^ (ctmark & ctmask); i.e. nfmask defines what bits to clear and ctmask what bits of the ctmark to XOR into the nfmark. ctmask and nfmask default to 0xFFFFFFFF. --restore-mark is only valid in the mangle table. The following mnemonics are available for --set-xmark: --and-mark bits Binary AND the ctmark with bits. (Mnemonic for --set-xmark 0/invbits, where invbits is the binary negation of bits.) --or-mark bits Binary OR the ctmark with bits. (Mnemonic for --set-xmark bits/bits.) --xor-mark bits Binary XOR the ctmark with bits. (Mnemonic for --set-xmark bits/0.) --set-mark value[/mask] Set the connection mark. If a mask is specified then only those bits set in the mask are modified. --save-mark [--mask mask] Copy the nfmark to the ctmark. If a mask is specified, only those bits are copied. --restore-mark [--mask mask] Copy the ctmark to the nfmark. If a mask is specified, only those bits are copied. This is only valid in the mangle table. CONNSECMARK This module copies security markings from packets to connections (if unlabeled), and from connections back to packets (also only if unla- beled). Typically used in conjunction with SECMARK, it is only valid in the mangle table. --save If the packet has a security marking, copy it to the connection if the connection is not marked. --restore If the packet does not have a security marking, and the connec- tion does, copy the security marking from the connection to the packet. DSCP This target allows to alter the value of the DSCP bits within the TOS header of the IPv4 packet. As this manipulates a packet, it can only be used in the mangle table. --set-dscp value Set the DSCP field to a numerical value (can be decimal or hex) --set-dscp-class class Set the DSCP field to a DiffServ class. HL This is used to modify the Hop Limit field in IPv6 header. The Hop Limit field is similar to what is known as TTL value in IPv4. Setting or incrementing the Hop Limit field can potentially be very dangerous, so it should be avoided at any cost. This target is only valid in man- gle table. Don’t ever set or increment the value on packets that leave your local network! --hl-set value Set the Hop Limit to ‘value’. --hl-dec value Decrement the Hop Limit ‘value’ times. --hl-inc value Increment the Hop Limit ‘value’ times. LOG Turn on kernel logging of matching packets. When this option is set for a rule, the Linux kernel will print some information on all match- ing packets (like most IPv6 IPv6-header fields) via the kernel log (where it can be read with dmesg or syslogd(8)). This is a "non-termi- nating target", i.e. rule traversal continues at the next rule. So if you want to LOG the packets you refuse, use two separate rules with the same matching criteria, first using target LOG then DROP (or REJECT). --log-level level Level of logging (numeric or see syslog.conf(5)). --log-prefix prefix Prefix log messages with the specified prefix; up to 29 letters long, and useful for distinguishing messages in the logs. --log-tcp-sequence Log TCP sequence numbers. This is a security risk if the log is readable by users. --log-tcp-options Log options from the TCP packet header. --log-ip-options Log options from the IPv6 packet header. --log-uid Log the userid of the process which generated the packet. MARK This target is used to set the Netfilter mark value associated with the packet. The target can only be used in the mangle table. It can, for example, be used in conjunction with routing based on fwmark (needs iproute2). The mark field is 32 bits wide. --set-xmark value[/mask] Zeroes out the bits given by mask and XORs value into the packet mark ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed. --set-mark value[/mask] Zeroes out the bits given by mask and ORs value into the packet mark. If mask is omitted, 0xFFFFFFFF is assumed. The following mnemonics are available: --and-mark bits Binary AND the nfmark with bits. (Mnemonic for --set-xmark 0/invbits, where invbits is the binary negation of bits.) --or-mark bits Binary OR the nfmark with bits. (Mnemonic for --set-xmark bits/bits.) --xor-mark bits Binary XOR the nfmark with bits. (Mnemonic for --set-xmark bits/0.) NFLOG This target provides logging of matching packets. When this target is set for a rule, the Linux kernel will pass the packet to the loaded logging backend to log the packet. This is usually used in combination with nfnetlink_log as logging backend, which will multicast the packet through a netlink socket to the specified multicast group. One or more userspace processes may subscribe to the group to receive the packets. Like LOG, this is a non-terminating target, i.e. rule traversal contin- ues at the next rule. --nflog-group nlgroup The netlink group (1 - 2^32-1) to which packets are (only appli- cable for nfnetlink_log). The default value is 0. --nflog-prefix prefix A prefix string to include in the log message, up to 64 charac- ters long, useful for distinguishing messages in the logs. --nflog-range size The number of bytes to be copied to userspace (only applicable for nfnetlink_log). nfnetlink_log instances may specify their own range, this option overrides it. --nflog-threshold size Number of packets to queue inside the kernel before sending them to userspace (only applicable for nfnetlink_log). Higher values result in less overhead per packet, but increase delay until the packets reach userspace. The default value is 1. NFQUEUE This target is an extension of the QUEUE target. As opposed to QUEUE, it allows you to put a packet into any specific queue, identified by its 16-bit queue number. It can only be used with Kernel versions 2.6.14 or later, since it requires the nfnetlink_queue kernel support. The queue-balance option was added in Linux 2.6.31, queue-bypass in 2.6.39. --queue-num value This specifies the QUEUE number to use. Valid queue numbers are 0 to 65535. The default value is 0. --queue-balance value:value This specifies a range of queues to use. Packets are then bal- anced across the given queues. This is useful for multicore systems: start multiple instances of the userspace program on queues x, x+1, .. x+n and use "--queue-balance x:x+n". Packets belonging to the same connection are put into the same nfqueue. --queue-bypass By default, if no userspace program is listening on an NFQUEUE, then all packets that are to be queued are dropped. When this option is used, the NFQUEUE rule is silently bypassed instead. The packet will move on to the next rule. NOTRACK This target disables connection tracking for all packets matching that rule. It can only be used in the raw table. RATEEST The RATEEST target collects statistics, performs rate estimation calcu- lation and saves the results for later evaluation using the rateest match. --rateest-name name Count matched packets into the pool referred to by name, which is freely choosable. --rateest-interval amount{s|ms|us} Rate measurement interval, in seconds, milliseconds or microsec- onds. --rateest-ewmalog value Rate measurement averaging time constant. REJECT This is used to send back an error packet in response to the matched packet: otherwise it is equivalent to DROP so it is a terminating TAR- GET, ending rule traversal. This target is only valid in the INPUT, FORWARD and OUTPUT chains, and user-defined chains which are only called from those chains. The following option controls the nature of the error packet returned: --reject-with type The type given can be icmp6-no-route, no-route, icmp6-adm-pro- hibited, adm-prohibited, icmp6-addr-unreachable, addr-unreach, icmp6-port-unreachable or port-unreach which return the appro- priate ICMPv6 error message (port-unreach is the default). Finally, the option tcp-reset can be used on rules which only match the TCP protocol: this causes a TCP RST packet to be sent back. This is mainly useful for blocking ident (113/tcp) probes which frequently occur when sending mail to broken mail hosts (which won’t accept your mail otherwise). tcp-reset can only be used with kernel versions 2.6.14 or later. SECMARK This is used to set the security mark value associated with the packet for use by security subsystems such as SELinux. It is only valid in the mangle table. The mark is 32 bits wide. --selctx security_context SET This modules adds and/or deletes entries from IP sets which can be defined by ipset(8). --add-set setname flag[,flag...] add the address(es)/port(s) of the packet to the sets --del-set setname flag[,flag...] delete the address(es)/port(s) of the packet from the sets where flags are src and/or dst specifications and there can be no more than six of them. Use of -j SET requires that ipset kernel support is provided. As stan- dard kernels do not ship this currently, the ipset or Xtables-addons package needs to be installed. TCPMSS This target allows to alter the MSS value of TCP SYN packets, to con- trol the maximum size for that connection (usually limiting it to your outgoing interface’s MTU minus 40 for IPv4 or 60 for IPv6, respec- tively). Of course, it can only be used in conjunction with -p tcp. It is only valid in the mangle table. This target is used to overcome criminally braindead ISPs or servers which block "ICMP Fragmentation Needed" or "ICMPv6 Packet Too Big" packets. The symptoms of this problem are that everything works fine from your Linux firewall/router, but machines behind it can never exchange large packets: 1) Web browsers connect, then hang with no data received. 2) Small mail works fine, but large emails hang. 3) ssh works fine, but scp hangs after initial handshaking. Workaround: activate this option and add a rule to your firewall con- figuration like: iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu --set-mss value Explicitly sets MSS option to specified value. If the MSS of the packet is already lower than value, it will not be increased (from Linux 2.6.25 onwards) to avoid more problems with hosts relying on a proper MSS. --clamp-mss-to-pmtu Automatically clamp MSS value to (path_MTU - 40 for IPv4; -60 for IPv6). This may not function as desired where asymmetric routes with differing path MTU exist — the kernel uses the path MTU which it would use to send packets from itself to the source and destination IP addresses. Prior to Linux 2.6.25, only the path MTU to the destination IP address was considered by this option; subsequent kernels also consider the path MTU to the source IP address. These options are mutually exclusive. TCPOPTSTRIP This target will strip TCP options off a TCP packet. (It will actually replace them by NO-OPs.) As such, you will need to add the -p tcp parameters. --strip-options option[,option...] Strip the given option(s). The options may be specified by TCP option number or by symbolic name. The list of recognized options can be obtained by calling iptables with -j TCPOPTSTRIP -h. TOS This module sets the Type of Service field in the IPv4 header (includ- ing the "precedence" bits) or the Priority field in the IPv6 header. Note that TOS shares the same bits as DSCP and ECN. The TOS target is only valid in the mangle table. --set-tos value[/mask] Zeroes out the bits given by mask and XORs value into the TOS/Priority field. If mask is omitted, 0xFF is assumed. --set-tos symbol You can specify a symbolic name when using the TOS target for IPv4. It implies a mask of 0xFF. The list of recognized TOS names can be obtained by calling iptables with -j TOS -h. The following mnemonics are available: --and-tos bits Binary AND the TOS value with bits. (Mnemonic for --set-tos 0/invbits, where invbits is the binary negation of bits.) --or-tos bits Binary OR the TOS value with bits. (Mnemonic for --set-tos bits/bits.) --xor-tos bits Binary XOR the TOS value with bits. (Mnemonic for --set-tos bits/0.) TPROXY This target is only valid in the mangle table, in the PREROUTING chain and user-defined chains which are only called from this chain. It redi- rects the packet to a local socket without changing the packet header in any way. It can also change the mark value which can then be used in advanced routing rules. It takes three options: --on-port port This specifies a destination port to use. It is a required option, 0 means the new destination port is the same as the original. This is only valid if the rule also specifies -p tcp or -p udp. --on-ip address This specifies a destination address to use. By default the address is the IP address of the incoming interface. This is only valid if the rule also specifies -p tcp or -p udp. --tproxy-mark value[/mask] Marks packets with the given value/mask. The fwmark value set here can be used by advanced routing. (Required for transparent proxying to work: otherwise these packets will get forwarded, which is probably not what you want.) TRACE This target marks packes so that the kernel will log every rule which match the packets as those traverse the tables, chains, rules. (The ipt_LOG or ip6t_LOG module is required for the logging.) The packets are logged with the string prefix: "TRACE: tablename:chain- name:type:rulenum " where type can be "rule" for plain rule, "return" for implicit rule at the end of a user defined chain and "policy" for the policy of the built in chains. It can only be used in the raw table. DIAGNOSTICS Various error messages are printed to standard error. The exit code is 0 for correct functioning. Errors which appear to be caused by invalid or abused command line parameters cause an exit code of 2, and other errors cause an exit code of 1. BUGS Bugs? What’s this? ;-) Well... the counters are not reliable on sparc64. COMPATIBILITY WITH IPCHAINS This ip6tables is very similar to ipchains by Rusty Russell. The main difference is that the chains INPUT and OUTPUT are only traversed for packets coming into the local host and originating from the local host respectively. Hence every packet only passes through one of the three chains (except loopback traffic, which involves both INPUT and OUTPUT chains); previously a forwarded packet would pass through all three. The other main difference is that -i refers to the input interface; -o refers to the output interface, and both are available for packets entering the FORWARD chain. There are several other changes in ip6tables. SEE ALSO ip6tables-save(8), ip6tables-restore(8), iptables(8), iptables-save(8), iptables-restore(8), libipq(3). The packet-filtering-HOWTO details iptables usage for packet filtering, the netfilter-extensions-HOWTO details the extensions that are not in the standard distribution, and the netfilter-hacking-HOWTO details the netfilter internals. See http://www.netfilter.org/. AUTHORS Rusty Russell wrote iptables, in early consultation with Michael Neul- ing. Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic packet selection framework in iptables, then wrote the mangle table, the owner match, the mark stuff, and ran around doing cool stuff every- where. James Morris wrote the TOS target, and tos match. Jozsef Kadlecsik wrote the REJECT target. Harald Welte wrote the ULOG and NFQUEUE target, the new libiptc, as well as TTL match+target and libipulog. The Netfilter Core Team is: Marc Boucher, Martin Josefsson, Yasuyuki Kozakai, Jozsef Kadlecsik, Patrick McHardy, James Morris, Pablo Neira Ayuso, Harald Welte and Rusty Russell. ip6tables man page created by Andras Kis-Szabo, based on iptables man page written by Herve Eychenne . iptables 1.4.4 IP6TABLES(8)

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