[c-nsp] Multicast Issue

Wed Apr 26 18:58:52 EDT 2006

This is on a native mode SUP2.

I just had my co-worker startup the client and I see this:

(10.a.b.c, 224.0.1.55), 00:07:16/00:00:10, flags: T
  Incoming interface: Vlan4, RPF nbr 0.0.0.0, RPF-MFD
  Outgoing interface list:
    Vlan1, Forward/Dense, 00:07:16/00:00:00, H

where 10.a.b.c is the IP address of the client.

Here is the output of some debugging:

y19w: IP: s=10.a.b.c (Vlan4) d=224.0.1.55 (Vlan1) len 92, mforward
1y19w: MRT: Create (10.a.b.c,224.0.1.55), RPF Vlan4/0.0.0.0
1y19w: MRT: WAVL Insert interface: Vlan1 in (10.a.b.c,224.0.1.55)
Successful
1y19w: MRT: Add Vlan1/224.0.1.55 to the olist of (10.a.b.c,
224.0.1.55), Forward state
1y19w: IP: MAC sa=0003.470b.6bce (Vlan4), IP last-hop=10.a.b.c
1y19w: IP: IP tos=0x0, len=78, id=0x34BF, ttl=1, prot=17
1y19w: IP: s=10.a.b.c (Vlan4) d=224.0.1.55 (Vlan1) len 92, mforward

Interestingly, the output of show mac-address-table multicast shows two
entries for 0100.5e00.0137:

4  0100.5e00.0137    static  Yes   --  Router
1  0100.5e00.0137    static  Yes   --  Gi4/16

The Vlan1 entry is my static entry. Why would the 6513 an entry in
Vlan4? The source of the packet is in Vlan4 but I don't understand why
that would create an entry in the mac address table. Isn't the table
only for destination MAC addresses? If so, why would an entry show up
for the source?

Thanks!
John
--

>>> Tim Stevenson <tstevens at cisco.com> 4/26/06 4:44:38 PM >>>
Do you see a source,group entry? You seem to be running dense mode, 
and DM fwding is always on the s,g never the *,g (the *,g is created 
but not used for fwding).

So you need to see a PC,224.0.1.55 mroute entry with vlan1 as an OIF.

BTW, what supervisor engine are you using, sup2 or sup720?

Also, you are sure the packets are not getting L3 switched (ie, that 
they're not dropping somewhere in vlan 1)?

Tim

At 02:37 PM 4/26/2006, John Neiberger pronounced:
>I've got an interesting issue that I think I'm tantalizingly close to
>solving but I haven't had to deal with multicast stuff in years.
>
>We have a PC on one subnet that is sourcing a multicast packet. I
need
>to get that packet to a device on another LAN that is not capable of
>sending IGMP joins. Here's the topology:
>
>PC *- 6513(IOS) *- 2950 *- Server
>
>In this case, the PC is sending out a single multicast packet trying
to
>reach the server. The packet does not reach the server because it
can't
>join the group. The multicast group is 224.0.1.55. The "server" is in
>Vlan1, so on the 6513 I have the following configured:
>
>int Vlan1
>  ...
>  ip igmp static-group 224.0.1.55
>!
>! That makes Vlan1 show up in the mroute table, but I still need to
>forward that packet out some particular interface, right? So...
>!
>mac-address-table static 0100.5e00.0137 vlan 1 interface
>GigabitEthernet4/16
>!
>!  That statically forwards traffic destined for that multicast
address
>out the interface leading to the Catalyst 2950
>
>On the 2950 I have the following:
>
>mac-address-table static 0100.5e00.0137 vlan 1 interface
>GigabitEthernet0/2
>
>That should forward the multicast traffic to the server hanging of
off
>g0/2. However, this isn't working. I've tinkered with a couple of
>different configs but nothing seems to work. Debugging shows that the
>multicast packet is making it to the 6513.
>
>1y19w: IP: s=10.a.b.c (Vlan4) d=224.0.1.55 (Vlan1) len 92, mforward
>
>The output of "show ip mroute 224.0.1.55" shows the following:
>
>(*, 224.0.1.55), 00:00:01/00:02:58, RP 0.0.0.0, flags: DC
>   Incoming interface: Null, RPF nbr 0.0.0.0
>   Outgoing interface list:
>     Vlan1, Forward/Dense, 00:00:01/00:00:00
>
>It looks to me like the 6513 should know where to forward the packets
>but it isn't working.
>
>Any ideas?
>
>Thanks!
>John
>--
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Tim Stevenson, tstevens at cisco.com 
Routing & Switching CCIE #5561
Technical Marketing Engineer, Catalyst 6500
Cisco Systems, http://www.cisco.com 
IP Phone: 408-526-6759
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