[c-nsp] Sup720, multicast bothers the CPU

[Chris Evans]

Also check the ttl if your packets.  If its 1 it will always hit the CPU
regardless of group address.
On Mar 25, 2011 6:01 AM, "Peter Rathlev" <peter at rathlev.dk> wrote:
> On Wed, 2011-03-23 at 20:55 +0100, Peter Rathlev wrote:
>> Thanks. We'll try just adding "ip igmp snooping querier" to the specific
>> SVI to see if this in itself would be enough. Next up we try "ip pim
>> sparse-mode" on the SVI and "ip multicast-routing" in global.
>>
>> I'll keep the list updated on how it went. :-)
>
> We now tried both adding an IGMP Querier and enabling multicast-routing
> and PIM. None of these things stopped the multicast traffic from hitting
> the CPU.
>
> I'm a little puzzled that we actually saw _some_ sources:
>
> xxx#sh ip igmp membership
> [...]
> *,239.255.255.253 10.26.46.78 00:02:41 02:46 2A Vl46
> *,239.255.255.250 10.26.46.77 00:02:43 02:46 2A Vl46
> *,224.0.1.40 10.26.46.254 00:02:43 02:53 2LA Vl46
> xxx#
>
> Just not from the "interesting" groups. We tried restarting both a
> receiver and a source to see if anything changed, and we never saw joins
> or "*,<something>".
>
> So a few questions more:
>
> 1) Could "offset != 0" somehow mean that the flows cannot be hardware
> switched at all? Every single packet has offset != 0, i.e. no packet
> observed with offset == 0. We were looking at both an RP SPAN
> session and a SPAN session covering the VLAN in question.
>
> 2) Could 224.0.0.0/24, which they use for this purpose though that's
> wrong, somehow be treated specially by a Sup720? Any chance it would
> help using 239.255.255.0/24 instead?
>
> Thanks in advance.
>
> --
> Peter
>
>
>
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