214 lines
3.6 KiB
HTML
214 lines
3.6 KiB
HTML
<HTML
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><HEAD
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><TITLE
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>Rules - routing policy database</TITLE
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TITLE="Simple source policy routing"
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><H1
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><A
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NAME="LARTC.RPDB"
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></A
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>Chapter 4. Rules - routing policy database</H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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>4.1. <A
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HREF="lartc.rpdb.simple.html"
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>Simple source policy routing</A
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></DT
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><DT
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>4.2. <A
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HREF="lartc.rpdb.multiple-links.html"
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>Routing for multiple uplinks/providers</A
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></DT
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><DD
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><DL
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><DT
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>4.2.1. <A
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HREF="lartc.rpdb.multiple-links.html#AEN258"
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>Split access</A
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></DT
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><DT
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>4.2.2. <A
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HREF="lartc.rpdb.multiple-links.html#AEN284"
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>Load balancing</A
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></DT
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></DL
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></DD
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></DL
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></DIV
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><P
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>If you have a large router, you may well cater for the needs of different
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people, who should be served differently. The routing policy database allows
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you to do this by having multiple sets of routing tables. </P
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><P
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>If you want to use this feature, make sure that your kernel is compiled with
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the "IP: advanced router" and "IP: policy routing" features.</P
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><P
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>When the kernel needs to make a routing decision, it finds out which table
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needs to be consulted. By default, there are three tables. The old 'route'
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tool modifies the main and local tables, as does the ip tool (by default).</P
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><P
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>The default rules:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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>[ahu@home ahu]$ ip rule list
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0: from all lookup local
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32766: from all lookup main
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32767: from all lookup default</PRE
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></FONT
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></TD
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></TR
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></TABLE
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><P
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>This lists the priority of all rules. We see that all rules apply to all
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packets ('from all'). We've seen the 'main' table before, it is output by
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<TT
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CLASS="USERINPUT"
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><B
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>ip route ls</B
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></TT
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>, but the 'local' and 'default' table are new.</P
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><P
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>If we want to do fancy things, we generate rules which point to different
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tables which allow us to override system wide routing rules.</P
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><P
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>For the exact semantics on what the kernel does when there are more matching
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rules, see Alexey's ip-cref documentation. </P
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></DIV
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>Prev</A
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> </TD
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><TD
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>Simple source policy routing</TD
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> |