Problems With Multicast Igmp Snooping; Troubleshooting Guidelines; Troubleshooting Commands - Cisco Nexus 1000V Troubleshooting Manual

Problems with Multicast IGMP Snooping

S e n d d o c u m e n t c o m m e n t s t o n e x u s 1 k - d o c f e e d b a c k @ c i s c o . c o m .
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Problems with Multicast IGMP Snooping
The operation of multicast IGMP snooping depends on the correct configuration of the upstream switch.
Because the IGMP process needs to know which upstream port connects to the router that supports IGMP
routing, you must turn on IP multicast routing on the upstream switch by issuing the
ip multicast-routing command.
The following example shows how to turn on global multicast-routing, configure an SVI interface, and
turn on the PIM routing protocol:
switch# conf terminal
Enter configuration commands, one per line.
switch(config)# ip multicast-routing
switch(config)# end
switch# conf terminal
Enter configuration commands, one per line.
switch(config)# int vlan159
switch(config-if)# ip pim dense-mode
switch(config-if)# end

Troubleshooting Guidelines

Follow these guidelines when troubleshooting multicast IGMP issues:
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Troubleshooting Commands

To troubleshoot issues with multicast IGMP snooping, use the following commands:
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Example 18-1 show cdp neighbor Command
n1000V# show cdp neighbor
Capability Codes: R - Router, T - Trans-Bridge, B - Source-Route-Bridge
Cisco Nexus 1000V Troubleshooting Guide, Release 4.2(1)SV2(2.1)
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IGMP queries are flooded to the whole VLAN.
IGMP reports are forwarded to the uplink port (the router ports).
Multicast data traffic is forwarded to uplink ports (the router ports).
Use the show ip igmp snooping command to verify that IGMP snooping is enabled.
Make sure the upstream switch has IGMP configured.
Use the show ip igmp snooping groups command to verify if the Nexus 1000V switch is configured
correctly and is ready to forward multicast traffic. In the displayed output of the command, look for
the letter R under the port heading. The R indicates that the VSM has learned the uplink router port
from the IGMP query that was sent by the upstream switch, and means that the Nexus 1000V is
ready to forward multicast traffic.
show cdp neighbor
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.
End with CNTL/Z.
End with CNTL/Z.
Chapter 18 Multicast IGMP
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