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Re: vr0 only working if tcpdump -n -i vr0 is running

Am 12.10.2011 um 23:38 schrieb Chuck Swiger:

> As you discovered, tcpdump is putting the NIC into promiscuous mode, so it 
> processes all packets it sees, rather than ignoring packets which it doesn't 
> believe it should listen to.

Ok, so without promiscious mode, the hardware is ignoring packets for which it 
believes that they are not addressed for it?

> This tends to indicate layer-2 problems such as it is not generating 
> ARPOP_REPLYs for its IP with the right MAC, or the ARP tables on other 
> machines in the network don't match.
> Running "tcpdump -exxn -s 0 arp"

This generates a lot of output, as I'm in a university network. Is there 
anything specific you want to know?

> and "arp -a" ought to be informative.

The output looks sane, it has the DHCP server and the gateway and all local 
machines behind my NAT.

> You might be able to work around the issue by convincing the thing which 
> wants a specific MAC to look for the MAC which your vr0 NIC originally has.

Well, as they want to know your hardware's MAC address and filter by that (only 
on the gateway, the rest always works), I gave them my laptop's MAC so that I 
can still use the laptop without my NetBSD router in case of emergency. But I 
could see if they can add an additional MAC. I'll ask on monday, this is the 
next time I can reach somebody who's resposible.

> You aren't trying to do proxy arp'ing or layer-2 bridging, by any chance...?

Well, I'm not doing that, but I have no idea what they are doing. The network 
is very strange here. It's by far one of the worst I've seen, you really would 
not expect that form a university.

> What does "signal" mean here?
> Ethernet link light?  Seeing traffic from the rest of the network?

Ethernet link light. I have a WiFi AP which only gets a link light if I reboot 
it several times, I got a few NICs which never find a link and I got a few 
devices (MacBook Pro, PowerBook) which always get a link.


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