[afnog] Packet Forwarding Issue with Linux

[Gerald Begumisa]

On Mon, Apr 11, 2011 at 3:23 PM, Hugo Lombard <hal at elizium.za.net> wrote:

>
> Oh dear, hope you get this solved before it goes up in smoke!
>

Me too :-).  It's barely limping along:

# dmesg
...
Buffer I/O error on device hda1, logical block 6458766
end_request: I/O error, dev hda, sector 114189383
...

It's a 5 year old clone that we've been using as our gateway.


>
> Judging from the MAC address, it would seem they're using a Cisco of
> some sort.  I've seen this behaviour a couple of times on Cisco.  All
> your ISP would need to do, is to issue a
>
>  clear arp interface <INTERFACE>
>
> on their router, with <INTERFACE> replaced by the name of the interface
> you're connected to.
>
> This will have the effect of clearing all entries on said interface, and
> if there's multiple people on the same interface, they might object, but
> in practice, it'll just requery the attached hosts and nobody should
> bump into any issues.
>

Thanks for this - this is great information to have on hand.


>
> It's kind of a feature on Cisco equipment that they're reluctant to
> update ARPs too often.  Some say it's to prevent ARP snooping attacks
> and such.
>
> You might also be able to play with arping to update the table, but I
> can't guarantee that it'll work.  I think something to the line of
>
>  /sbin/arping -A -I eth2 1.2.3.42
>
> might do the needful.  Might be worth trying, but the best would be if
> they just clear their ARP cache on the interface.
>

Thanks!  We'll be sure to try arping as well.


Regards,
Gerald
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