[c-nsp] Nexus 7K - Multicast Question

[Tim Stevenson]

Hi Antonio,

Can you please describe the exact topology here? 
Which interfaces you're using, what they're connected to, and where is the RP?

One thing to be aware of with NXOS is that things 
only show up in sh ip mroute if the client 
protocol/process (eg IGMP in this case) has 
reason to feed them there. sh ip mroute is 
basically looking at the MRIB view of the world and nothing else.

WRT the ip igmp join-group command, it does two 
things: one is it causes that interface to send 
IGMP joins for that group out that interface as 
if it were a host. The other is that, if the 
router is PIM DR on that interface, it feeds the 
*G & the OIF to the MRIB. It's only at that point 
you'll see the entry in sh ip mroute. Otherwise, 
you'll only see it in the IGMP group membership table, ie, sh ip igmp group.

My guess here is you're not DR on this interface, 
so I assume there's another router on the segment 
that IS the DR. If you check the mrouting there I 
suspect you'll see the *G entry joined to the RPT 
(driven by the IGMP joins sent on that segment 
from the router w/the join-group command).

WRT the loopback "working", what you're seeing is 
that this router is now the only means by which 
to reach that 'network segment' (ie, it's 
obviously going to be DR on its own loopback) so 
it will report the *G & OIF to the MRIB and then 
you'll see the entry in sh ip mroute.

Hope that helps,
Tim


At 03:24 AM 10/1/2011, Antonio Soares contended:

>This is lab environment, I'm just testing basic multicast features with
>nexus.
>
>The command reference says the following:
>
>"When you enter this command, the traffic generated is handled by the device
>CPU, not the hardware."
>
><http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/multicast/c>http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/multicast/c
>ommand/reference/mcr_cmds_i.html#wp1230243
>
>The "ip igmp static-group" was replaced by the command:
>
>ip igmp static-oif
>
><http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/multicast/c>http://www.cisco.com/en/US/docs/switches/datacenter/sw/5_x/nx-os/multicast/c
>ommand/reference/mcr_cmds_i.html#wp1034808
>
>When I have the igmp joing on the physical interface, the (*,G) entry is
>created then it disappears. But I see the (*,G) entry on the RP and I
>verified that the traffic is actually sent to the nexus.
>
>
>Thanks.
>
>Regards,
>
>Antonio Soares, CCIE #18473 (R&S/SP)
>amsoares at netcabo.pt
><http://www.ccie18473.net>http://www.ccie18473.net
>
>
>-----Original Message-----
>From: cisco-nsp-bounces at puck.nether.net
>[<mailto:cisco-nsp-bounces at puck.nether.net>mailto:cisco-nsp-bounces at puck.nether.net] 
>On Behalf Of Phil Mayers
>Sent: sábado, 1 de Outubro de 2011 10:49
>To: cisco-nsp at puck.nether.net
>Subject: Re: [c-nsp] Nexus 7K - Multicast Question
>
>On 10/01/2011 01:31 AM, Antonio Soares wrote:
> > Hello group,
> >
> > Anyone knows why the "ip igmp join-group" does not work on a physical
> > interface but it works fine on a loopback interface ?
>
>"ip igmp join-group" is a CPU command; it makes the CPU join the group
>and receive the packets. I imagine this might not work on a hardware
>platform, with an interface which will be processed in hardware.
>
>Are you sure you don't want "ip igmp static-group"?
>
>What's your use case?
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>
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Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Distinguished Technical Marketing Engineer, Cisco Nexus 7000
Cisco - http://www.cisco.com
IP Phone: 408-526-6759
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