Multicasting testing

Unanswered Question
Aug 14th, 2008

I am going to do some multicast testing on a 4900M. I am using an XIA traffic generator. I am told to send the traffic to the switch multicast mac. where is this or how can I find it

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Giuseppe Larosa Thu, 08/14/2008 - 10:57

Hello Yolanda,

the multicast traffic is mapped to a subset of L2 MAC multicast address.

the mapping rule is the following:

the multicast MAC address 48 bit is:

0x 01005e + 1binary0 + last 23 bits of multicast IP address

last 23 bits = last significant 23 bits of the 4 octet multicast IP address

32 addresses are mapped to a single multicast MAC address

the 1 the last significant bit in the first byte is called I/G bit it says it is multicast when set to 1

You need to send traffic to the mapped MAC address for your group.

Instead unicast traffic has to be sent to the router /L3 switch MAC address

Note: To be able to send multicast traffic successfully from IXIA port1 to IXIA port2 you need to configure IXIA port2 to send IGMP join and later IGMP reports for the multicast group you want to send traffic to.

Hope to help

Giuseppe

newbie Thu, 08/14/2008 - 11:49

Thanks for the response. I am still a little confused. When setting up the IXIA how do I know what the mapped MAC address for the group is? Also, I guess I have to set up a group on the swicth then or do you mean by group a vlan group.

Giuseppe Larosa Fri, 08/15/2008 - 09:02

Hello Yolanda,

the multicast MAC address can be derived from the IPv4 multicast address

example:

225.0.0.37

becomes:

0100.5e00.0025

so this is the L2 destination of your traffic

when I speak of multicast group I mean the IPv4 multicast ip address itself

So joining a group means send IGMP messages about 225.0.0.37

Here group has nothing to do with vlan groups or other

On the switch you need to enable ipv4 multicast routing and ip pim sparse-dense mode on all L3 SVI Vlans of interest.

Try to download this introduction to multicast

http://tools.cisco.com/search/display?url=http%3A%2F%2Fwww.cisco.com%2Fen%2FUS%2Fprod%2Fcollateral%2Fiosswrel%2Fps6537%2Fps6552%2Fprod_presentation0900aecd80310883.pdf&pos=1&strqueryid=2&websessionid=qrDYkeGDbWaT9yZJuLdlQ7p

and multicast config on 4900M

http://cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/46sg/configuration/guide/mcastmls.html

Hope to help

Giuseppe

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