em0, VLAN and bpf(?) trouble w/RELENG_5
tbyte at OTEL.net
Tue Nov 9 11:09:10 PST 2004
Robert Watson wrote:
>On Mon, 8 Nov 2004 astesin at ukrtelecom.net wrote:
>>The problem. From time to time, vlan0 stops passing packets at all. At
>>this moments, Catalyst stops seeing MAC of vlan0 (it's the same MAC as
>>em0) in the mantione VLAN (untagged VLAN is also configured at em0 and
>>works fine!). This means that `show mac-address-table vlan XX' command
>>on Catalyst don't show the MAC.
>>The problem can be easily repeated manually. It's enough just to issue a
>>command like `trafshow -I vlan0' of `tcpdump -I vlan0' and voila! vlan0
>>is out of business, no packets are going through.
>Hmm. Could I get you to try/investigate a few things:
>(1) If you run tcpdump on the em0 interface itself, does the same thing
>(2) When vlan0 wedges, do you still see traffic on em0, and can you
> generate traffic on em0 that's picked up by the switch?
>(3) Do other vlan pseudo-interfaces wedge under similar circumstances?
>(4) Could you try running with "debug.mpsafenet=0" in loader.conf (reboot
> for it to take effect) and see if that makes a difference?
>(5) Does it matter whether you enter promiscuous mode using BPF -- i.e.,
> "tcpdump -p -i vlan0" vs w/o the -p flag?
>(6) When vlan0 is in the wedged condition, how "no packets" is it? Can
> you send packets but not receieve, or receive packets and not send?
>Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
>robert at fledge.watson.org Principal Research Scientist, McAfee Research
>freebsd-current at freebsd.org mailing list
>To unsubscribe, send any mail to "freebsd-current-unsubscribe at freebsd.org"
This seam to happen only with promiscuous mode set. It doesn't
happen when you use -p with tcpdump or trafshow.
I suspect that the problem is somewhere in hardware vlan tagging.
Possibly in promiscuous mode driver thinks that the
adapter tags/untags packets but it doesn't (just a thoght ...).
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