netdev - Re: increase the number of routing tables

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Message-ID: <1327804887.2805.20.camel@edumazet-laptop>
Date:	Sun, 29 Jan 2012 03:41:27 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Simon Chen <simonchennj@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: increase the number of routing tables

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 

# cat /etc/iproute2/rt_tables
#
# reserved values
#
255	local
254	main
253	default
0	unspec
#
# local
#
#1	inr.ruhep

3000 test3000

# ip route list table 3000
1.2.3.4 dev eth0  scope link 


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