Re: [OT] Ethernet Hostrouting / arp(watch)
Also sprach Richard Mittendorfer <delist@gmx.net> (Thu, 18 Aug 2005
01:50:26 +0200):
> Also sprach Guido Heumann <listguido@web.de> (Thu, 18 Aug 2005
> 01:08:00 +0200):
> > Richard Mittendorfer schrieb:
> [...]
> > > arpwatch: flip flop 192.168.2.251 0:2:44:16:9c:63
> > > (0:2:44:5b:74:ef) eth1
> > > ^^^^^^^^^^^^^^^eth1 MAC
> > > arpwatch: flip flop 192.168.2.251 0:2:44:5b:74:ef
> > > (0:2:44:16:9c:63) eth1
> > > ^^^^^^^^^^^^^^^eth0 MAC
> > >
> > > ..und das innerhalb 5 Minuten. Selbiges auf eth0. Nun koennt es
> > > sich um die !$#^rtl8139 handeln oder aber um den arpcache. Ein
> > > Vesuch das [...]
Aha! Man lernt ja nie aus... ;)
http://linux-ip.net/html/ether-arp.html
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2.1.4. The ARP Flux Problem
When a linux box is connected to a network segment with multiple network
cards, a potential problem with the link layer address to IP address
mapping can occur. The machine may respond to ARP requests from both
Ethernet interfaces. On the machine creating the ARP request, these
multiple answers can cause confusion, or worse yet, non-deterministic
population of the ARP cache. Known as ARP flux [13], this can lead to
the possibly puzzling effect that an IP migrates non-deterministically
through multiple link layer addresses. It's important to understand that
ARP flux typically only affects hosts which have multiple physical
connections to the same medium or broadcast domain.
This is a simple illustration of the problem in a network where a server
has two Ethernet adapters connected to the same media segment. They need
not have IP addresses in the same IP network for the ARP reply to be
generated by each interface. Note the first two replies received in
response to the ARP broadcast request. These replies arrive from
conflicting link layer addresses in response to this request. Also
notice the greater time required for the sending and receiving hosts to
process the broadcast ARP request frames than the unicast frames which
follow (probes two and three).
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sl ritch
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