Re: em device hangs on ifconfig alias ...

Robert Watson said the following on 7/7/06 7:17 AM:
> I just left a "tcpdump -n arp host 10.10.64.40" on a third machine > sniffing around and tested all em module versions I had (the stock 6.1, > 6-STABLE and 6-STABLE with your patch), but got silence on all three:

That's odd. I've tested it on CURRENT and I could see the ARP packet. Are you sure you patched correctly? If so I have to build a RELENG_6 machine and give it try.

Is it possible you're seeing an interaction between the reset generated as part of IP address changing, and the time it takes to negotiate link? It's possible that the arp packets are being eaten during the link negotiation, so for systems negotiating quickly (or not at all) then the arp packet is seen on other hosts, and otherwise not...

Looks like this is exactly what happens.

I was able to see it by running two tcpdump instances - one on the EM machine running in background and another running elsewhere on the same subnet.

So on the EM machine the arp packet actually gets generated by em(4) and caught by the tcpdump running there:

EM# tcpdump -n arp and ether src 00:04:23:b5:1b:ff &
EM#
EM# ifconfig em1 inet alias 10.10.64.40
EM# 11:28:37.178946 arp who-has 10.10.64.40 tell 10.10.64.40
EM#

But it doesn't reach the other tcpdump instance running on another host. It seems that the arp packet gets killed before leaving the EM machine, due to the card initialization or something else.

I tried sending it manually with arping, just to make sure both tcpdumps operate properly and yes, the packet got delivered to both.

I think that I have patched, built and loaded the em(4) kernel module correctly. After applying the patch there were no rejects, before building the module I intentionally appended " (patched)" to its version string in if_em.c, and could see that in dmesg every time I loaded the module:
em1: <Intel(R) PRO/1000 Network Connection Version - 3.2.18 (patched)>

Regards,
Atanas

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