[c-nsp] Nexus 7K - Multicast Question

Tue Oct 4 21:17:26 EDT 2011

Hi Antonio,

Just would like to be perfectly clear what's 
going on here: "sh ip mroute" on NXOS shows the 
MRIB. The MRIB is specifically for multicast *routing* information.

In the original scenario you described, where the 
join-group is configured on the upstream (RPF) 
interface and the 7k is not the PIM DR, no 
*mrouting* is required or being performed - the 
7k is behaving as a host, ie, sending IGMP joins 
to pull the traffic. So you'll only see that 
state in sh ip igmp groups, not sh ip mroute. 
Note that you should still see the multicast 
traffic arriving on the n7k RPF interface (thru sh int).

In the case of the loopback, mrouting *is* 
required, ie, in order to multicast route the 
multicast from the RPF interface to the loopback 
- so IGMP feeds the group information and OIF to 
the MRIB to enable the mrouting.

This is all just a side effect of the modular 
architecture of the NXOS software - IGMP, the 
MRIB, PIM, MSDP etc etc are all independent 
processes and each maintains its own state based 
on what it needs to know; and each only tells 
other process(es) about that state when its actually necessary.

Hope that helps,
Tim

At 04:56 PM 10/4/2011, Antonio Soares contended:
>You’re right, it works if the N7K is the DR is 
>that segment. Now the mroute table shows what I was expecting:
>
>N7K12(config-if)# sh ip mroute
>IP Multicast Routing Table for VRF "default"
>
>(*, 232.0.0.0/8), uptime: 00:13:29, pim ip
>   Incoming interface: Null, RPF nbr: 0.0.0.0
>   Outgoing interface list: (count: 0)
>
>(*, 239.1.2.3/32), uptime: 00:04:55, pim ip igmp
>   Incoming interface: Ethernet1/27, RPF nbr: 10.12.2.2
>   Outgoing interface list: (count: 1)
>     Ethernet1/27, uptime: 00:00:30, igmp, (RPF)
>
>(10.12.1.1/32, 239.1.2.3/32), uptime: 00:04:53, ip mrib pim
>   Incoming interface: Ethernet1/27, RPF nbr: 10.12.2.2
>   Outgoing interface list: (count: 1)
>     Ethernet1/27, uptime: 00:00:30, mrib, (RPF)
>
>N7K12(config-if)#
>
>
>Thank you for clarifying this difference between IOS and NXOS.
>
>
>Regards,
>
>Antonio Soares, CCIE #18473 (R&S/SP)
><mailto:amsoares at netcabo.pt>amsoares at netcabo.pt
>http://www.ccie18473.net
>
>
>From: Tim Stevenson [mailto:tstevens at cisco.com]
>Sent: domingo, 2 de Outubro de 2011 01:35
>To: Antonio Soares; Phil Mayers; cisco-nsp at puck.nether.net
>Subject: RE: [c-nsp] Nexus 7K - Multicast Question
>
>Interface e1/27 on n7k12 appears to be connected 
>to g2/2 on the 6500. I rest my case. ;)
>
>Tim
>
>At 12:40 PM 10/1/2011, Antonio Soares contended:
>
>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
>
>
>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>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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>
>
>
>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
>********************************************************
>The contents of this message may be *Cisco Confidential*
>and are intended for the specified recipients only.
>
>
>
>
>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
>********************************************************
>The contents of this message may be *Cisco Confidential*
>and are intended for the specified recipients only.

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
********************************************************
The contents of this message may be *Cisco Confidential*
and are intended for the specified recipients only.