[LARTC] Route cache

[Ard van Breemen]

Hi,

On Tue, Apr 18, 2006 at 09:30:18AM +0300, Andrei Sandu wrote:
>    I have a P4 @ 3Ghz router running Debian. It shapes traffic ( about
> 500-600 classes ), about 1000 iptables rules, and it does BGP too, so i get
> about
> 1300+ routes in the routing table. The problem is the load is too high on

That's not so much:
avb at YYY:~$ ip ro sh|wc -l
188583
Yes, that's the internet with peering and all...

> this system. I found a solution to my problem, turning off the route cache,
> but i dont know how to implement it,

You realise that your solution doesn't really sound good? ;-)

>    I was wondering if anyone found a way to disable the route caching system
> inside the kernel, to improve router performance in high traffic conditions.

Again: turning off route caching really does not sound good.

Especially if you have different routes.
What you need to do is increase your cache thresholds...
ard at XXX(master):~$ ip ro sh cache|wc -l
  41180
This system does a lot of traffic, and it still is cleaning it's
nose.

Depending on where your system is, you should put stuff into your
sysctl.conf:

net/ipv4/neigh/default/gc_thresh1=8192
net/ipv4/neigh/default/gc_thresh2=16384
net/ipv4/neigh/default/gc_thresh3=32768

net/ipv4/route/gc_elasticity=8
net/ipv4/route/gc_interval=30
net/ipv4/route/gc_min_interval=2
net/ipv4/route/gc_thresh=?

etc...

Anyway: I don't think that routing is really your issue.
Maybe you should look into optimising the shaping and/or iptables
ruleset.
ard at XXX(master):~$ sudo iptables -L -n|wc -l 
   2166
ard at XXX(master):~$ sudo iptables -L -n -t nat|wc -l 
    192

etc...

And of course, the BIG question: did you do a:
insmod ip_conntrack hashsize=4194304
?
Having a small hashsize for the connection tracking table is of
course the biggest problem for most users.

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