Re: [gentoo-user] ARP-Caching of non-link-local adresses

[Pandu Poluan <pandu@poluan.info>]

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On Jan 4, 2012 11:20 PM, "Peter Pan" <osaka@gmx.net> wrote:
>
> Hi list,
>
>
>
> I’m kind of despair.
>
> The history: We recently brought up a new firewall with Gentoo.
>
> There are (for my finding) some big nets behind this firewall (1x public
/24, 2x public /27, 1x public /26, at least 2 private /24).
>
> Filtering is done via iptables and snort should jump as IPS on
software-bridge br0. If it helps: There is also ip rule involved for
source-based routing.
>
>
>
> The new firewall replaces an older Gentoo-system which did not show this
behavior. We therefore copied several configfiles from the old to the new
one.
>
>
>
> After getting it live, it runs well for a few hours and then becomes
unreachable (also for hosts behind the bridge).
>
> Dmesg / kern.log stated at this time a neighbor table overflow and
indeed, arp –n | wc –l showed a lot of entry’s.
>
>
>
> As Google suggested, We then adjusted /proc/sys/net/ipv4/neigh/default/
to:
>
> gc_thershold1 -> 8192
>
> gc_thershold2 -> 16384
>
> gc_thershold3 -> 32768
>
>
>
> Fireing an “arp –d $bogus-ip-adress” is failing with „SIOCDARP(dontpub):
Network is unreachable”, adding –i br0 doesn’t fail, but does not remove
the line in the arp-table (it only says “incomplete” after greping arp -n
again)..
>
> Therefore we are currently killing the arp-cache  with “ip link set arp
off dev br0 && ip link set arp on dev br0” by a cronjob.
>
>
>
> The combination of these workarounds are keeping the firewall reachable
and “alive”.
>
>
>
> After stabilizing, we looked at the output of arp –n and noticed, that
about 99(.999)% of the roundabout 11.000 (and rising) arp-cache-entry’s
contained public addresses for which the bridge of the firewall should not
feel responsible (e.g. the public Google-dns-resolver and a load of more).
>
> The MAC-entry for these public addresses is always the one of our router,
which is for sure the correct next hop.
>
>
>
> But from my understanding,  it should arp-cache only “our” net’s directly
at the cable and not those public ones.
>
> It looks like a configuration-issue, but I don’t know, where to start
looking. I’ve already checked the default-gateway, netmasks,
broadcast-addresses and to me, they are looking fine, so any poke where to
start looking is greatly appreciated.
>
>
>
> In case it will help, I attached the /etc/conf.d/net, ifconfig –a and
route -n.
>
> If something else is needed, feel free to ask.
>
>
>
> Hope, anyone can help.
>

Try turning off proxy ARP on the internal and/or external interfaces.

Rgds,

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