[ECOS] bug in ARP FSM with fragmented packets?

Emmanuel Coullien coullien.emmanuel@gmail.com
Mon Jan 21 13:31:00 GMT 2008

On Mon, Jan 21, 2008 at 12:18:16PM +0100, J?rgen Lambrecht wrote:
> Hello,
> I'm investigating a problem where UDP packets get lost when there is an
> ARP table timeout.
> - It only happens with UDP, not with TCP; IPv4.
> - It only happens with fragmented IP packets, so with UDP packets bigger
> than the Ethernet MTU of 1518 Bytes.
> - I use freeBSD stack, version from CVS end 2007
> This is what I see with Ethereal: The application receives a UDP request
> packet, and must send back a UDP reply packet. Instead an ARP
> request/reply happens, and the packet gets lost.
> Using static ARP table entries solves the problem of course, but that is
> not acceptable.
> Has anybody seen such a problem before?
> Or has anybody a clue where to start looking?


We met this same problem and we solved it temporary by changing the
arpt_keep to 24h in if_ether.c (just for the test). But we don't know
if we can really do it.
Why isn't it acceptable and do you know what are the consequences if
we use a such long timeout ?

Emmanuel Coullien

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