linux-kernel - Re: Routing 600+ vlan's via linux problems (looks like arp problems)

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Date:	Thu, 3 May 2007 22:55:23 +0200
From:	Willy Tarreau <w@....eu>
To:	Øyvind Vågen Jægtnes <lorrides@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Routing 600+ vlan's via linux problems (looks like arp problems)

On Thu, May 03, 2007 at 10:53:41PM +0200, Willy Tarreau wrote:
> On Thu, May 03, 2007 at 10:25:48PM +0200, Øyvind Vågen Jægtnes wrote:
> > Hi,
> > 
> > We have a one gigabit internet connection that is normally
> > routed by a hardware juniper router. The drive in this is down
> > and we need to use a linux machine (Pentium D 3 ghz) as a
> > temporary router.
> > Now setting up all the 600 vlans and assigning ip addresses
> > is no problem. We have testet all by using a laptop, setting up
> > 600 vlan interfaces on this and running dhcpclient on all.
> > This worked just fine, all the interfaces got address.
> > 
> > Now for the real setup.
> > We closed the mac of the juniper to the network card that
> > would be connected to the internal LAN, set up the interfaces,
> > and swapped cables. This worked fine for approximately 100
> > of the computers that are connected, but the rest would not
> > get IP. The connected 100 computers were routed just fine.
> > 
> > What we think the problem is, is that the arp cache on the
> > linux router seems strange. It can resolve the MAC for the
> > 100 clients that actually got through.
> > For the rest all we see in the arp cache is (incomplete)
> 
> I suspect that your arp cache is full (128 entries by default).
> Check /proc/sys/net/ipv4/neigh/gc_thresh1 (128 for me). You can
                                ^ insert /default/ here.

> set it as high as gc_thresh2 (512 for me), and I don't know what
> happens above.

Willy

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