[Gllug] Weird networking problem with 2.6 kernel

[john at sinodun.org.uk]

I've just set up a new box running Sarge and brought it into school.  It
worked fine at home but networking is very flaky when it's on the school
LAN.  (Settings received by DHCP in both cases.)

I've noticed a very odd phenomenon when I boot the machine up.  Using a
separate machine to run tcpdump I see an endless stream of ARP Who Has
requests once the new machine tries to do some networking.  Like this:

11:49:08.775393 00:50:8b:91:04:57 > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: arp who-has 192.168.100.16 tell 192.168.101.251
11:49:09.798605 00:50:8b:91:04:57 > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: arp who-has 192.168.100.16 tell 192.168.101.251
11:49:10.821037 00:50:8b:91:04:57 > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: arp who-has 192.168.100.16 tell 192.168.101.251
11:49:11.845939 00:50:8b:91:04:57 > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: arp who-has 192.168.100.16 tell 192.168.101.251
11:49:12.870747 00:50:8b:91:04:57 > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: arp who-has 192.168.100.16 tell 192.168.101.251
11:49:13.893114 00:50:8b:91:04:57 > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: arp who-has 192.168.100.16 tell 192.168.101.251

100.16 is one of our main servers and 101.251 is the address allocated to
the new box.  Examining the ARP cache on the new box shows it already
knows the MAC address of 100.16, and the really odd thing is that the
packets continue to appear on the LAN for several minutes *after* the new
box has been physically disconnected from it!  The packets carry the new
box's MAC address and yet are not emanating from the new box.  Anyone any
idea what could be doing this?  Some other piece of hardware reflecting
the packets back onto the LAN?

If I boot the new box with a 2.4 kernel there are no problems.

John
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