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arp oddities



Hello,

In 2.7-2.8stable it is not possible to delete a specific arp
entry by using 'arp -d' but only by doing a 'route delete' on the
corresponding IP address. While this is np as soon as one knows
it, I'm not sure if this is wanted and considered a feature (?)

Then, we experience rather strange problems with arp and vlan. 
The parent interface is set up as follows:

fxp1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	media: Ethernet autoselect (100baseTX full-duplex)
	status: active
	inet 192.168.168.1 netmask 0xffffff80 broadcast 192.168.168.127

The vlan setup is (ips diff.):

vlan4: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        vlan: 4 parent interface: fxp1
        inet 111.111.111.1 netmask 0xffffff80 broadcast 111.111.111.127

and the connected cisco 2924XL-EN is set up to tag all incoming
traffic on ports as from vlan 4 before forwarding them to the
trunk port on which the OpenBSD box listens. No vlan setup is done
on the connected hosts, only "111.111.111.1" is set up as default
gateway, which works well for *BSD and HP-UX.

The problem is that, from time to time, and especially when asked
by Linux boxes, the OpenBSD box does not answer arp requests,
therefore decreasing availability of affected servers significantly.

Also strange is that, according to tcpdump, ~90% arp questions
come in on vlan4 while ~10% questions (99% of which are broadcasts)
and 100% answer appear on fxp1. The Linux box question is arriving
as a non-broadcast message at fxp1. During that time, the OpenBSD
router still holds the arp and routing entry for the Linux box,
although it does not answer the arp requests for it's own vlan4's
address.

While setting up static entries in each hosts or one that does
public distribution surely helps, installing Linux via FTP is still
almost impossible. Besides, I also wonder if there's a mistake in
our setup or in the way arp/vlan/routing interact in OpenBSD.

Maybe someone more enlightened can shed some light on this.

TIA,
Volker

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Volker T. Mueller               	     Technik, hp9000

MMP Solutionsproviding          	     Tel. +49 761 4794090
Boetzinger Strasse 29a          	     Fax. +49 761 4794099
79111 Freiburg i. Br.           	     http://datafarm.de
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