netdev - Re: increase the number of routing tables

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Date:	Mon, 30 Jan 2012 07:25:46 -0500
From:	Thomas Graf <tgraf@...radead.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Simon Chen <simonchennj@...il.com>, netdev@...r.kernel.org
Subject: Re: increase the number of routing tables

On Sun, Jan 29, 2012 at 03:41:27AM +0100, Eric Dumazet wrote:
> Le samedi 28 janvier 2012 à 21:20 -0500, Simon Chen a écrit :
> > Hey folks,
> > 
> > To my limited knowledge, Linux currently supports 256 (255?) routing
> > tables defined in /etc/iproute2/rt_tables.
> > 
> > Is there a way to increase this number to something much larger? Are
> > there performance/scalability concerns there? I am trying to have
> > customized routing table for each IP address (using "ip rule add from
> > xxx table yyy"). I am not sure exactly how many IPs I'll handle, but
> > certainly more than 255...
> > 
> 
> Its is possible, but probably not scalable.
> 
> You really should not have too many "ip rule" entries, since they are
> evaluated linearly.
> 
> The limit being ~32768 rules
> 
> # ip rule
> 0:	from all lookup local 
> 32763:	from all to 1.2.3.7 lookup test3000 
> 32766:	from all lookup main 
> 32767:	from all lookup default 

I've run into these scalability issues a while ago which is
why I've added the goto action allowing to build a tree like
structures:

0:	from all lookup local 
10:     from eth0 goto 4000
[possibly thousands of rules]
3999:   from all goto 32763
4000:   from all to 1.1.1.1 lookup foo
[...]
32763:	from all to 1.2.3.7 lookup test3000 
32766:	from all lookup main 
32767:	from all lookup default 
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