Debugging Multicast Routing
Problem
You appetite to use alter functions to abstract botheration with multicast forwarding.
Solution
Cisco routers accept several advantageous alter appearance that you can use to abstract multicast problems. The aboriginal is a accepted command that shows how the router maintains its multicast acquisition tables back it hears from sources and accumulation members:
Router#debug ip mrouting
You can watch the absolute multicast packets for a accurate accumulation application the command:
Router#debug ip mpacket 239.5.5.55
And the added frequently advantageous multicast alter command looks accurately at IGMP information:
Router#debug ip igmp
Discussion
As with all debugging commands, you charge to be acutely accurate because sometimes the arduous aggregate of the achievement can beat the router. So it is usually astute to try these commands one at a time, and attenuate all debugging with the command undebug all afore aggravating the abutting command.
The aboriginal alter command, alter ip mrouting, shows how the router creates, updates, and deletes multicast acquisition information:
Router#terminal monitor
Router#debug ip mrouting
IP multicast acquisition debugging is on
Router#
17:20:27: MRT: Create (192.168.5.1/32, 239.5.5.55), RPF Ethernet0/0.0.0.0, PC 0x33A89D8
17:20:43: MRT: Update (*, 224.0.1.40), RPF Null, PC 0x339F96C
17:20:49: MRT: Delete (192.168.3.2/32, 224.0.1.39), PC 0x33AB26A
17:21:43: MRT: Update (*, 224.0.1.40), RPF Null, PC 0x339F96C
17:21:49: MRT: Create (192.168.3.2/32, 224.0.1.39), RPF Ethernet0/192.168.5.1, PC 0x33A89D8
17:22:13: MRT: Delete (*, 224.0.1.1), PC 0x33AB26A
17:22:24: MRT: Create (*, 224.0.1.1), RPF Null, PC 0x33A8890
17:22:46: MRT: Update (*, 224.0.1.40), RPF Null, PC 0x339F96C
17:22:46: MRT: Update (*, 224.0.1.40), RPF Null, PC 0x339F96C
In this example, the aboriginal band creates a accumulation access for 239.5.5.55 with the antecedent 192.168.5.1 in acknowledgment to accepting a multicast packet from this source. You can additionally see a cardinal of entries actuality for the Auto-RP groups, 224.0.1.39 and 224.0.1.39. These are the aftereffect of routers chatting amidst themselves to ensure that a abiding RP exists for the network.
The abutting command, alter ip mpacket, shows alone multicast packets. Looking at packet-level alter traces is consistently decidedly alarming because of the achievability of cutting the router. In this example, we accept asked the router to appearance alone the accumulation 239.5.5.55, which we accept acclimated as an archetype throughout this chapter:
Router#debug ip mpacket 239.5.5.55
IP multicast packets debugging is on for accumulation 239.5.5.55
May 10 16:18:40.870: IP: s=192.168.5.2 (Ethernet1) d=239.5.5.55 (TokenRing0) len
114, mforward
May 10 16:18:40.874: IP: s=192.168.5.2 (Ethernet1) d=239.5.5.55 (Ethernet0) len
114, mforward
May 10 16:18:40.878: IP: s=192.168.5.2 (TokenRing0) d=239.5.5.55 len 122, not RP
F interface
May 10 16:18:40.890: IP: s=192.168.254.5 (TokenRing0) d=239.5.5.55 (Ethernet1) l
en 122, mforward
May 10 16:18:40.890: IP: s=192.168.254.5 (TokenRing0) d=239.5.5.55 (Ethernet0) l
en 122, mforward
As you can see, a packet was accustomed on interface Ethernet1 with the antecedent abode of 192.168.5.2 for this group. The router anon angry about and forwarded this packet to interface TokenRing0 and Ethernet0. A abbreviate time later, it accustomed addition packet for this accumulation with the aforementioned antecedent abode from TokenRing0. However it doesn't advanced this packet forth because it was not accustomed on the RPF interface. That is, the router looks in its acquisition table and realizes that this is not the way that it should accept accustomed this packet, so it drops it to abstain loops.
The router again receives a multicast packet for this aforementioned accumulation on interface TokenRing0, but this time with a antecedent abode of 192.168.254.5. It assiduously this packet over to both Ethernet1 and Ethernet0.
It is important to agenda that this command tells you annihilation about accumulation membership. If accessories accompany or leave this group, you will not see them this way. To do that, you charge to attending at the achievement of alter ip igmp:
Router#debug ip igmp
IGMP debugging is on
17:34:17: IGMP: Send v2 Query on Ethernet0 to 224.0.0.1
17:34:18: IGMP: Send v2 Query on Ethernet1 to 224.0.0.1
17:34:18: IGMP: Set address adjournment time to 8.6 abnormal for 224.0.1.40 on Ethernet1
17:34:18: IGMP: Send v2 Query on TokenRing0 to 224.0.0.1
17:34:19: IGMP: Accustomed v2 Address from 192.168.1.104 (Ethernet0) for 239.5.5.55
17:34:21: IGMP: Accustomed v2 Address from 192.168.5.2 (Ethernet1) or 224.0.1.40
17:34:21: IGMP: Cancel address for 224.0.1.40 on Ethernet1
17:34:23: IGMP: Accustomed v2 Address from 192.168.3.2 (TokenRing0) for 239.5.5.55
17:34:24: IGMP: Accustomed v2 Address from 192.168.3.2 (TokenRing0) for 224.0.1.39
17:34:25: IGMP: Accustomed v2 Address from 192.168.3.2 (TokenRing0) for 224.0.1.1
17:34:26: IGMP: Accustomed v2 Address from 192.168.1.100 (Ethernet0) for 239.255.255.250
17:34:27: IGMP: Accustomed v2 Address from 192.168.1.104 (Ethernet0) for 239.5.5.55
17:34:32: IGMP: Accustomed v2 Address from 192.168.1.104 (Ethernet0) for 239.5.5.55
This alter trace shows a brace of absorbing contest active in a accomplished lot of router-to-router multicast chatter, so you accept to attending anxiously at the accumulation addresses to makes abiding that you're seeing the absorbing data. The accumulation 224.0.0.1 is the All Systems group, which is acclimated for bounded articulation chatter. It is rarely absorbing for multicast acquisition because it is advised to be absolutely local, and all multicast able accessories are consistently members. The groups 224.0.1.39 and 224.0.1.40 are acclimated by the Auto-RP agreement to acquiesce routers to allotment advice about the PIM-SM RPs for the network.
So, unless you are aggravating to alter an Auto-RP problem, the alone absolutely absorbing advice in this trace are the entries for the groups 239.5.5.55 and 239.255.255.250. The accessory 192.168.1.104 has abutting the aboriginal group, and sends several IGMP Address packets to accomplish abiding that it has auspiciously abutting that group. The accessory 192.168.1.100, on the added hand, has been a affiliate of 239.255.255.250 for some time, and it sends alone a distinct packet to ensure that it will abide to accept this group.
A abbreviate time later, the accessory 192.168.1.104 leaves the accumulation 239.5.5.55, as apparent in the afterward trace:
17:34:54: IGMP: Accustomed Leave from 192.168.1.104 (Ethernet0) for 239.5.5.55
17:34:54: IGMP: Send v2 Query on Ethernet0 to 239.5.5.55
17:34:55: IGMP: Send v2 Query on Ethernet0 to 239.5.5.55
17:34:57: IGMP: Deleting 239.5.5.55 on Ethernet0
Since this was the aftermost accepted affiliate of this accumulation on this segment, the router responds to the IGMP Leave bulletin with an IGMP Query. It tries alert to see if there are still any added accessories absorbed in continuing to see this group, and again deletes it