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Webcast-Catalyst9k
New Member

multicast on serial interface

When I put a Serial interface into a multicast group(and this is the only one interface which run pim),like this:

ip multicast-routing

interface serial 3/0

ip pim sparse-dense-mode

ip igmp join 239.255.1.1

show ip mroute display:

(*, 239.254.1.1), 00:15:32/00:00:00, RP 0.0.0.0, flags: DCL

Incoming interface: Null, RPF nbr 0.0.0.0

Outgoing interface list:

Serial3/0, Forward/Sparse-Dense, 00:00:12/00:00:00

I found I can't ping 239.255.1.1 on the router.

But if I put a Ethernet interface into a multicast group(and this interface is the only one which run pim),like this:

ip multicast-routing

interface Fas 0/0

ip pim sparse-dense-mode

ip igmp join-group 239.255.1.1

show ip mroute display:

(*, 239.254.1.1), 00:00:01/00:00:00, RP 0.0.0.0, flags: DCL

Incoming interface: Null, RPF nbr 0.0.0.0

Outgoing interface list:

FastEthernet0/0, Forward/Sparse-Dense, 00:00:01/00:00:00

I found I can ping 239.255.1.1 now !!

Why this situation happen?

2 REPLIES
New Member

Re: multicast on serial interface

BTW,the 239.255.1.1 in the configure ought to be replace by 239.254.1.1.

I try this on three images:

c3640-i-mz.122-6.bin

c2600-js56i-mz.120-8b.bin

c2500-i-l.120-23.bin

the result is same.

Maybe Serial interface can't be the only pim interface on the router?

Cisco Employee

Re: multicast on serial interface

This is normal behavior. In order to ping the local serial interface, the packet needs to go to the other side of the serial link and be forwarded back by the peer router. That is the case even when you do a unicast ping to the local address for a serial interface. This is obviously not the case with an Ethernet interface hence this working properly when you try it on the Ethernet interface.

If you want to test the "ip igmp join-group" on the serial interface, ping from the other side of the serial link.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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