multicast "mac not built" on debug ip mrouting

Unanswered Question
Jan 29th, 2008
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We activate multicast routing on our network and on different site with switch 3750 and 3550 we can't have traffic. With the same configuration on a switch 4500 all is ok.

We're using PIM-SM with RP and shared-tree.

On attachments, there is debug PIM and mrouting on different switches.

What is "MAC not built" in debug ip mrouting on 3750 ?


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curhed Thu, 03/27/2008 - 13:43
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Hi, I've got exactly the same issue and it seems hard to find info about it.


interface FastEthernet0/2

description to Mcast destination (VLC Player)

no switchport

ip address

ip pim passive

interface FastEthernet0/4

description to Mcast source (VLC Player

switchport access vlan 10

switchport mode access

switchport nonegotiate

spanning-tree portfast

interface FastEthernet0/6

description -- to Routers 2811 network

no switchport

ip address

ip pim sparse-mode

interface Vlan10

ip address

ip pim passive

ip pim autorp listener

ip pim send-rp-announce FastEthernet0/6 scope 10

ip pim send-rp-discovery FastEthernet0/6 scope 10

debug ip mrouting:

"MRT(0): Update FastEthernet0/2/ in the olist of (*,, Forward state - MAC not built"

show ip mroute summary:

(*,, 03:43:39/00:02:53, RP, OIF count: 3, flags: SJC

Comments surely appretiated...


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