はじめに
あまり使わないが、たまに使うとき忘れるのでメモ。
ip rule チートシート
概要
ip rule コマンドは、Linux のポリシーベースルーティング (PBR) を管理するためのツール。
ポリシーベースルーティングとは
ポリシールーティング（Policy-Based Routing, PBR）は、 通常のルーティングテーブル（main）とは異なるルールを適用し、 パケットの送信先や経路を柔軟に制御する仕組み。
通常のルーティング（デスティネーションベースのルーティング）は 「宛先 IP アドレス」に基づいてルートを決定するが、ポリシールーティングでは 送信元 IP や特定のプロトコル、インターフェース、ポートなどに基づいて異なるルートを適用可能。
基本的な仕組み
- IPパケットを送信したいと思う
- PBRで、利用するルーティングテーブル決定
- 利用するルーティングテーブルにルーティング情報があれば利用。なければPBRの走査を再開。
なお、数字が小さいほうが優先度が高いことに注意。
感想
いままで考えることもなくip routeの出力を見ていた。
しかし、ip routeで出力されるのはmainテーブルで、そのmainテーブルがip ruleで利用されるように設定されていたから、
ip routeで確認するので良かったのだった。
なお、manにある通り、0, 32766, 32767の3つのruleは最初から設定されている。
ルールの表示
現在のルーティングルールを表示する。オプションはないし、ルーティングテーブルのようにテーブルはない。
ip rule show
出力例
0: from all lookup local
32766: from all lookup main
32767: from all lookup default
10000: to 100.64.0.0/10 lookup 100
気づくこと
まずlocalテーブルが確認され、その後にmainテーブルが確認される。 mainテーブルは普段見るとおりだが、localテーブルには何が入っているのだろうか。 Dockerのubuntu:jammyで確認してみる。
local 127.0.0.0/8 dev lo proto kernel scope host src 127.0.0.1
local 127.0.0.1 dev lo proto kernel scope host src 127.0.0.1
broadcast 127.255.255.255 dev lo proto kernel scope link src 127.0.0.1
local 172.17.0.2 dev eth0 proto kernel scope host src 172.17.0.2
broadcast 172.17.255.255 dev eth0 proto kernel scope link src 172.17.0.2
上記のように、local関連のPBRのruleが書かれていた。
なお、172.17.0.0/16はdockerのネットワーク。
また、127.0.0.0/8のサブネットは全て、ここでloデバイスで通信することになることがわかった。
(src 127.0.0.1なので、fromとtoでアドレスを変えられるのか、知らなかった)
また、mainテーブルにはなかったlocalやbroadcastのような指定もあった。
語彙
fwmark
Firewall Mark。
ルールの追加・削除
特定のルーティングテーブルを使用するルールを追加する。
ip rule add from <SOURCE_IP> table <TABLE_ID>
特定のルーティングテーブルを使用するルールを削除する。
ip rule del from <SOURCE_IP> table <TABLE_ID>
優先度を指定してルールを追加する。
ip rule add from <SOURCE_IP> table <TABLE_ID> priority <PRIORITY>
特定の宛先アドレスへのルートテーブルを設定する。
ip rule add to <DESTINATION_IP> table <TABLE_ID>
マーク付きパケットのルール設定
特定のマークが付いたパケットに対してルートテーブルを適用する。
ip rule add fwmark <MARK> table <TABLE_ID>
ルールの優先順位設定
特定のルールの優先順位を変更する。
ip rule add from <SOURCE_IP> table <TABLE_ID> priority <PRIORITY>
ルールのフラッシュ（全削除）
すべてのポリシールールを削除する。
ip rule flush
よく使うオプション
| 説明 | オプション |
|---|---|
| ルールを表示する | show |
| ルールを追加する | add |
| ルールを削除する | del |
| 優先度を指定する | priority |
| 特定の送信元アドレスに適用する | from |
| 特定の宛先アドレスに適用する | to |
| パケットマークでルールを適用する | fwmark |
| すべてのルールを削除する | flush |
参考リンク
man ip ruleより引用
IP-RULE(8) Linux IP-RULE(8)
NAME
ip-rule - routing policy database management
SYNOPSIS
ip [ OPTIONS ] rule { COMMAND | help }
ip rule [ list [ SELECTOR ]]
ip rule { add | del } SELECTOR ACTION
ip rule { flush | save | restore }
SELECTOR := [ not ] [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark FWMARK[/MASK] ] [ iif STRING ] [ oif STRING ] [ pref NUMBER ] [ l3mdev
] [ uidrange NUMBER-NUMBER ] [ ipproto PROTOCOL ] [ sport [ NUMBER | NUMBER-NUMBER ] ] [ dport [ NUMBER | NUMBER-NUMBER ] ] [ tun_id
TUN_ID ]
ACTION := [ table TABLE_ID ] [ protocol PROTO ] [ nat ADDRESS ] [ realms [SRCREALM/]DSTREALM ] [ goto NUMBER ] SUPPRESSOR
SUPPRESSOR := [ suppress_prefixlength NUMBER ] [ suppress_ifgroup GROUP ]
TABLE_ID := [ local | main | default | NUMBER ]
DESCRIPTION
ip rule manipulates rules in the routing policy database control the route selection algorithm.
Classic routing algorithms used in the Internet make routing decisions based only on the destination address of packets (and in theory, but
not in practice, on the TOS field).
In some circumstances we want to route packets differently depending not only on destination addresses, but also on other packet fields:
source address, IP protocol, transport protocol ports or even packet payload. This task is called 'policy routing'.
To solve this task, the conventional destination based routing table, ordered according to the longest match rule, is replaced with a 'routing
policy database' (or RPDB), which selects routes by executing some set of rules.
Each policy routing rule consists of a selector and an action predicate. The RPDB is scanned in order of decreasing priority (note that lower
number means higher priority, see the description of PREFERENCE below). The selector of each rule is applied to {source address, destination
address, incoming interface, tos, fwmark} and, if the selector matches the packet, the action is performed. The action predicate may return
with success. In this case, it will either give a route or failure indication and the RPDB lookup is terminated. Otherwise, the RPDB program
continues with the next rule.
Semantically, the natural action is to select the nexthop and the output device.
At startup time the kernel configures the default RPDB consisting of three rules:
1. Priority: 0, Selector: match anything, Action: lookup routing table local (ID 255). The local table is a special routing table con‐
taining high priority control routes for local and broadcast addresses.
2. Priority: 32766, Selector: match anything, Action: lookup routing table main (ID 254). The main table is the normal routing table con‐
taining all non-policy routes. This rule may be deleted and/or overridden with other ones by the administrator.
3. Priority: 32767, Selector: match anything, Action: lookup routing table default (ID 253). The default table is empty. It is reserved
for some post-processing if no previous default rules selected the packet. This rule may also be deleted.
Each RPDB entry has additional attributes. F.e. each rule has a pointer to some routing table. NAT and masquerading rules have an attribute to
select new IP address to translate/masquerade. Besides that, rules have some optional attributes, which routes have, namely realms. These
values do not override those contained in the routing tables. They are only used if the route did not select any attributes.
The RPDB may contain rules of the following types:
unicast - the rule prescribes to return the route found in the routing table referenced by the rule.
blackhole - the rule prescribes to silently drop the packet.
unreachable - the rule prescribes to generate a 'Network is unreachable' error.
prohibit - the rule prescribes to generate 'Communication is administratively prohibited' error.
nat - the rule prescribes to translate the source address of the IP packet into some other value.
ip rule add - insert a new rule
ip rule delete - delete a rule
type TYPE (default)
the type of this rule. The list of valid types was given in the previous subsection.
from PREFIX
select the source prefix to match.
to PREFIX
select the destination prefix to match.
iif NAME
select the incoming device to match. If the interface is loopback, the rule only matches packets originating from this host.
This means that you may create separate routing tables for forwarded and local packets and, hence, completely segregate them.
oif NAME
select the outgoing device to match. The outgoing interface is only available for packets originating from local sockets that
are bound to a device.
tos TOS
dsfield TOS
select the TOS value to match.
fwmark MARK
select the fwmark value to match.
uidrange NUMBER-NUMBER
select the uid value to match.
ipproto PROTOCOL
select the ip protocol value to match.
sport NUMBER | NUMBER-NUMBER
select the source port value to match. supports port range.
dport NUMBER | NUMBER-NUMBER
select the destination port value to match. supports port range.
priority PREFERENCE
the priority of this rule. PREFERENCE is an unsigned integer value, higher number means lower priority, and rules get processed
in order of increasing number. Each rule should have an explicitly set unique priority value. The options preference and order
are synonyms with priority.
table TABLEID
the routing table identifier to lookup if the rule selector matches. It is also possible to use lookup instead of table.
protocol PROTO
the routing protocol who installed the rule in question. As an example when zebra installs a rule it would get RTPROT_ZEBRA as
the installing protocol.
suppress_prefixlength NUMBER
reject routing decisions that have a prefix length of NUMBER or less.
suppress_ifgroup GROUP
reject routing decisions that use a device belonging to the interface group GROUP.
realms FROM/TO
Realms to select if the rule matched and the routing table lookup succeeded. Realm TO is only used if the route did not select
any realm.
nat ADDRESS
The base of the IP address block to translate (for source addresses). The ADDRESS may be either the start of the block of NAT
addresses (selected by NAT routes) or a local host address (or even zero). In the last case the router does not translate the
packets, but masquerades them to this address. Using map-to instead of nat means the same thing.
Warning: Changes to the RPDB made with these commands do not become active immediately. It is assumed that after a script fin‐
ishes a batch of updates, it flushes the routing cache with ip route flush cache.
ip rule flush - also dumps all the deleted rules.
protocol PROTO
Select the originating protocol.
ip rule show - list rules
This command has no arguments. The options list or lst are synonyms with show.
ip rule save
protocol PROTO
Select the originating protocol.
save rules table information to stdout
This command behaves like ip rule show except that the output is raw data suitable for passing to ip rule restore.
ip rule restore
restore rules table information from stdin
This command expects to read a data stream as returned from ip rule save. It will attempt to restore the rules table information ex‐
actly as it was at the time of the save. Any rules already in the table are left unchanged, and duplicates are not ignored.
SEE ALSO
ip(8)
AUTHOR
Original Manpage by Michail Litvak <[email protected]>
iproute2 20 Dec 2011 IP-RULE(8)