Subject: Re: Strange Trouble with the network on NetBSD 1.6.2 STABLE
To: MAHE, Franck <>
From: None <>
List: netbsd-users
Date: 02/27/2006 19:27:16

On Mon, Feb 27, 2006 at 06:01:26PM +0100, MAHE, Franck wrote:
> Here is the result of some troubleshooting tasks:
> 1-       After a reboot, the system is not up on the network (Not at all,
> because the other systems see the MAC Address of this box after a ping but
> without reply)
> 2-       On the NetBSD system, ifconfig & netstat are OK (With a little alias
> on it), but unable to ping other system, but the MAC Address of other systems
> are OK.
> 3-       Launch of tcpdump on the affected NIC, and surprise, the network is
> UP & Running

I had a similar experience with a Windows based network where I
installed (in dual boot) a NetBSD OS. The case is not identical but the
reasons may be similar.

Everything had to do with the Ethernet layer, namely the MAC address,
and the rarp caches (on the Windows nodes).
In my case, the Windows running on the machine on which I installed
NetBSD had an Ethernet card whose driver was misconfigured: user had
blindly entered a wrong MAC address---the option to give it was to let
the driver know which one, if several same cards present, to drive---and
Windows was able (!) to lie about the MAC address. Hence other nodes had
cached a wrong combination of MAC and IP. When I rebooted under NetBSD,
NetBSD was using the correct MAC address, so packets sent were resent,
but not with the MAC address but after rarp resolution, hence with the
wrong. When back, having the wrong MAC they were dropped.

In promiscuous mode, every packet is passed to the upper layer---not
only the ones matching the MAC for Ethernet---, hence if
the IP matched, the packet is treated. So using tcpdump(8) makes
apparently things working.

Have you tried to purge the rarp caches? After the reboot is the NetBSD
node using an IP address previously allocated to another node---still
caches holding the wrong association etc.

Hope this can give you some clues.
Thierry Laronde (Alceste) <tlaronde +AT+ polynum +dot+ com>
Key fingerprint = 0FF7 E906 FBAF FE95 FD89  250D 52B1 AE95 6006 F40C