Wireless router with 2 MACs: okay with mswin, not with Linux ?

From: Mark Lord
Date: Mon Sep 25 2006 - 17:15:03 EST

Hi all,

I'm posting this from a hotel which has a wireless AP (B+G) for guests.
It took me several hours to figure out how to get the connection working
with my 2.6.18 notebook -- works just fine with other guests' mswin machines.

WEP is used, and is set up and working just fine: I can access the AP's
built-in web interface without any troubles. But..

The AP has two MAC addresses:

# arping -c1 -I eth1
ARPING from eth1
Unicast reply from [00:11:F5:BA:67:AA] 2.164ms
Unicast reply from [00:11:F5:77:38:C2] 5.696ms
Sent 1 probes (1 broadcast(s))
Received 2 response(s)

The first MAC can connect locally to the AP, but not outside.
The second MAC can connect locally and/or outside.

Linux only seems to ever use the first (no good) MAC for the AP,
rather than the second. Whenever I try an outside access, the AP sends a gratuitous ARP reply, telling my machine to use the other MAC.
This seems to be ignored by Linux, but heeded by Windows.

For now, I've just written a small script to detect such a situation,
and to set a static ARP mapping for the second MAC. This works, but is way
beyond "normal usage" for most people.

Surely there's a flag or something to have the kernel cope with this?

Mark Lord
Real-Time Remedies Inc.

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