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Beginner

Multicast replication

Hi,

 

I read some docs(BRKDCT-3101) on CISCO live which talks about multicast replication.

Needed clarification on a few concepts:

 

1) There is an internal group id which is used and multiple (S,G) entries 

     share the same group id. Does each mroute map to an internal group?

N9K# bcm-shell mod 6 "ipmc table show"
SRC IP ADDRESS     MC IP ADDRESS     MC GROUP  VID VRF COS HWIDX CLASS HIT
13.13.13.14            239.10.10.10          0x2000007   0     1    0     75680    1        no
0.0.0.0                    239.10.10.10          0x2000007   0     1    0      86578 2 no

   

2) What is a replication group? 

 

I am trying to connect the dots from control plane (mroute) to what happens

inside the ASIC.  How does a mroute (Source IP, Group IP, OIF list) get mapped and replicated internally ?

 

Thank you,

Vij

 

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2 REPLIES 2
Hall of Fame Expert

Re: Multicast replication

Hello Vij,

you are looking at a detailed session about Nexus 9000.

I think slide 19 provides in a graphic way how a multicast packet is handled.

 

 

My guess a replication group is the list of modules and ports that should receive a multicast stream.

Remember that there is not a one to one corrispondence between an IPv4 multicast address and the corresponding MAC address: only the less significant 23 bits are mapped on the MAC address so 32 IPv4 multicast addresses share the same MAC address.

 

 

Hope to help

Giuseppe

 

Beginner

Re: Multicast replication

Hi Giuseppe,

 

Thank you for the reply. I was actually looking for some additional details.

I found the picture in the attached file on the net.

It shows the various blocks, but doesn't elaborate on how a route entry in 

MRIB gets mapped to a hardware entry in ASIC and how the replication 

happens. There seems to be multiple steps involved in ASIC and that's 

what i'm looking for.

 

Regards,

Arut

 

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