To troubleshoot issues with multicast IGMP snooping, use the following commands:
You can use the show cdp neighbor command because IGMP uses the packet VLAN to forward IGMP packets to the VSM, which is the same mechanism that CDP uses. However, if you have disabled the CDP protocol on the upstream switch using the no cdp enable command, then the show cdp neighbor command will not display any information.
Example 18-1 show cdp neighbor Command
n1000V# show cdp neighbor
Capability Codes: R - Router, T - Trans-Bridge, B - Source-Route-Bridge
S - Switch, H - Host, I - IGMP, r - Repeater,
V - VoIP-Phone, D - Remotely-Managed-Device,
Device ID Local Intrfce Hldtme Capability Platform Port ID
n1000V Eth3/2 179 R S I WS-C6506-E Gig5/16
n1000V Eth3/4 179 R S I WS-C6506-E Gig5/23
Use the show ip igmp groups command to make sure IGMP snooping is enabled on the VLAN.
Example 18-2 show ip igmp snooping vlan Command
n1000V# show ip igmp snooping vlan 159
IGMP Snooping information for vlan 159
IGMP snooping enabled <-- IGMP SNOOPING is enabled for vlan 159
IGMPv3 Explicit tracking enabled (initializing, time-left: 00:03:20)
IGMPv2 Fast leave disabled
IGMPv1/v2 Report suppression enabled
IGMPv3 Report suppression disabled
Router port detection using PIM Hellos, IGMP Queries
Number of router-ports: 0
Number of groups: 0show ip igmp snooping
- show ip igmp snooping groups
- debug ip igmp snooping vlan
Example 18-3 debug ip igmp snooping vlan Command
n1000V(config)# debug ip igmp snooping vlan
2008 Sep 2 13:29:36.125661 igmp: SNOOP: <vlan 159> Process a valid IGMP packet
2008 Sep 2 13:29:36.126005 igmp: SNOOP: <vlan 159> Received v2 report: group 184.108.40.206 fro 220.127.116.11 on Vethernet3
2008 Sep 2 13:29:36.126086 igmp: SNOOP: <vlan 159> Added oif Vethernet3 for (*, 18.104.22.168) entry
2008 Sep 2 13:29:36.126157 igmp: SNOOP: <vlan 159> Forwarding report for (*, 22.214.171.124) came on Vethernet3
2008 Sep 2 13:29:36.126225 igmp: SNOOP: <vlan 159> Forwarding the packet to router-ports
2008 Sep 2 13:29:36.126323 igmp: SNOOP: <vlan 159> Forwarding packet to router-port Ethernet3/6 (iod 42)
On the VSM, use the following command:
- module vem module-number execute vemcmd show vlan
In Example 18-4, the output shows that LTL 18 corresponds to vmnic3, and LTL 47 corresponds to VM fedora8, interface eth0.
The multicast group table for 126.96.36.199, shows the interfaces the VEM will forward to when it receives multicast traffic for group 188.8.131.52. If fedora8 has multicast group 184.108.40.206 on its eth0 interface, then LTL 47 should be in the multicast group table for 220.127.116.11.
LTL 18 is also in multicast group 18.104.22.168, which means it is a VM and generates multicast traffic to 22.214.171.124. The traffic will be forwarded to vmnic3, which is the uplink to the upstream switch.
The multicast group table entry for 0.0.0.0 serves as a default route. If any multicast group traffic does not match any of the multilcast group, the address will use the default route, which means, in this case, that the traffic will be forwarded to an upstream switch through vmnic3.
Example 18-4 module vem module-number execute vemcmd show vlan Command
n1000V# module vem 3 execute vemcmd show vlan 159
BD 159, vdc 1, vlan 159, 3 ports
Group 126.96.36.199 RID 1 Multicast LTL 4408
Group 0.0.0.0 RID 2 Multicast LTL 4407