Re: [c-nsp] Nexus 7K - Multicast Question

Tue, 04 Oct 2011 18:21:19 -0700 

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:amsoa...@netcabo.pt>amsoa...@netcabo.pt
http://www.ccie18473.net


From: Tim Stevenson [mailto:tstev...@cisco.com]
Sent: domingo, 2 de Outubro de 2011 01:35
To: Antonio Soares; Phil Mayers; cisco-nsp@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:amsoa...@netcabo.pt>amsoa...@netcabo.pt
http://www.ccie18473.net


From: Tim Stevenson [ mailto:tstev...@cisco.com]
Sent: sábado, 1 de Outubro de 2011 16:06
To: Antonio Soares; Phil Mayers; cisco-nsp@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)
amsoa...@netcabo.pt
<http://www.ccie18473.net>http://www.ccie18473.net


-----Original Message-----
From: cisco-nsp-boun...@puck.nether.net

[ 
<mailto:cisco-nsp-boun...@puck.nether.net>mailto:cisco-nsp-boun...@puck.nether.net] 
On Behalf Of Phil Mayers

Sent: sábado, 1 de Outubro de 2011 10:49
To: cisco-nsp@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, tstev...@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, tstev...@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, tstev...@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.



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