[c-nsp] Cisco 4900M and Layer2 Broadcasts

[Justin Krejci]

Is the layer 3 traffic multicast? Your indication of HA makes me suspect it is and perhaps you have a multicast snooping/filtering on the Cisco or some other related limiter setting.

Just a total guess without any configs or other pertinent data.



-----Original Message-----
From: Ivan [cisco-nsp at itpro.co.nz]
Received: Saturday, 28 Jun 2014, 5:10PM
To: cisco-nsp [cisco-nsp at puck.nether.net]
Subject: Re: [c-nsp] Cisco 4900M and Layer2 Broadcasts

Sorry to respond to my own post but I have some further thoughts that
may be useful.  The traffic ends up being broadcast at layer 2 (dest MAC
address ff:ff:ff:ff:ff:ff) but the IPv4 payload is generally unicast.
So I am thinking perhaps the 4900M could be "getting upset" with these
packets.  Not really expecting the 4900M to look higher than layer 2 of
these packets though as vlan does not have SVI.

Ivan

On 28/Jun/2014 10:17 p.m., Ivan wrote:
> I am hoping someone may have come across an issue I am seeing on a Cisco
> 4900M running 15.1(2)SG3.
>
> I have a device connected to an interface sending traffic from it's own
> MAC address to MAC address ff:ff:ff:ff:ff:ff.  When the layer 3 protocol
> is IPv6 I see this going out other port in the same vlan as the source -
> all good.  When the layer 3 protocol is IPv4 the frames seem to go into
> a black hole - very bad.  I have confirmed all this with packet captures.
>
> I have poked around but cam find any indication of the issue.  I will be
> logging a TAC case in the next day or two for this but would be
> interested to hear if anyone else has seen this.
>
> Thanks
>
> Ivan
>
> PS.  Not really looking to get into the details of the connected devices
> etc - just some HA type traffic using layer 2 over a vlan.
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