Wake on LAN, tcpdump weirdness with two ethernet interfaces

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To: Misc OpenBSD <misc@...>
Date: Wednesday, October 24, 2007 - 11:41 am

I'm noticing some strangeness in conjunction with WOL(*), which seems
not to be working and am not sure where the problem lies(**).

The machine launching the packets has two interfaces, re0 and em0, with
the receiving machine connected to re0. The machine does not wake up
either using port 9 or port 40000.

A bit of strangeness in the diagnostics is that tcpdump appears not to
register and packets from or to re0. It does not catch any packets on
re0, even from nmap -P0 -e re0 -T5 a.b.c.d

tcpdump -i re0 ip proto 17

whereas the following catches packets, even from wol, when sent to
addresses on em0.

tcpdump -i em0 ip proto 17

Route shows the following:

Internet:
Destination Gateway Flags Refs Use Mtu Interface
a.b.c.d 00:0f:1f:78:82:07 UHLc 1 8629 - re0

and when the machine is already on, I can ping and connect via ssh.

pfctl -s rules
are as simple as possible:
scrub in all fragment reassemble
pass in all flags S/SA keep state
pass out all flags S/SA keep state

What's up with tcpdump and, more importantly, wol?

-Lars

(*) Installed using pgk_add:
http://www.openbsd.org/4.1_packages/i386/wol-0.7.1p1.tgz-long.html

(**) Hardware is a Dell DHP on which I've set the BIOS to allow remote
wakeup and have the lowpower mode (which hinders remote wakeup) off.

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Wake on LAN, tcpdump weirdness with two ethernet interfaces, Lars Noodén, (Wed Oct 24, 11:41 am)