[c-nsp] Nexus 7K - Multicast Question

Sat Oct 1 15:40:43 EDT 2011

Hello Tim,

Very simple setup:

N7K11===CAT6500===N7K12

The RP is the CAT6500. The relevant configs bellow:

CAT6500 (The RP):

ip multicast-routing

!

interface Loopback0

ip address 3.3.3.3 255.255.255.255

ip pim sparse-mode

!

interface GigabitEthernet2/1

ip address 10.12.1.2 255.255.255.0

ip pim sparse-mode

!

interface GigabitEthernet2/2

ip address 10.12.2.2 255.255.255.0

ip pim sparse-mode

no ip mroute-cache

!

ip pim rp-address 3.3.3.3

!

N7K11 (The source):

feature ospf

feature pim

interface Ethernet1/27

  ip address 10.12.1.1/24

  ip router ospf 1 area 0.0.0.0

  ip pim sparse-mode

  no shutdown

ip pim rp-address 3.3.3.3 group-list 224.0.0.0/4

ip pim ssm range 232.0.0.0/8

N7K12 (The destination)

feature ospf

feature pim

interface Ethernet1/27

  ip address 10.12.2.1/24

  ip router ospf 1 area 0.0.0.0

  ip pim sparse-mode

  ip igmp join-group 239.1.2.3

  no shutdown

ip pim rp-address 3.3.3.3 group-list 224.0.0.0/4

ip pim ssm range 232.0.0.0/8

It works if the ip igmp join is moved to the loopback interface on the
N7K12.

Thanks.

Regards,

Antonio Soares, CCIE #18473 (R&S/SP)
 <mailto:amsoares at netcabo.pt> amsoares at netcabo.pt

 <http://www.ccie18473.net> http://www.ccie18473.net

From: Tim Stevenson [mailto:tstevens at cisco.com] 
Sent: sábado, 1 de Outubro de 2011 16:06
To: Antonio Soares; Phil Mayers; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Nexus 7K - Multicast Question

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

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

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

-----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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Tim Stevenson, tstevens at cisco.com
Routing & Switching CCIE #5561
Distinguished Technical Marketing Engineer, Cisco Nexus 7000
Cisco - http://www.cisco.com <http://www.cisco.com/> 
IP Phone: 408-526-6759
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