Multicast Data Fails To Reach Receivers - 3Com MSR 50 Series Configuration Manual

Multicast Data Fails to
Reach Receivers
5 Check that the multicast static route matches the specified routing policy. If a
routing policy was specified when the multicast static route was configured, enter
the display route-policy command to check the configured routing policy.
Symptom
The multicast data can reach some routers but fails to reach the last hop router.
Analysis
When a router receives a multicast packet, it decrements the TTL value of the
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multicast packet by 1 and recalculates the checksum value. The router then
forwards the packet to all outgoing interfaces. If the multicast minimum-ttl
command is configured on the outgoing interfaces, the TTL value of the packet
must be larger than the configured minimum TTL value; otherwise, the packet
will be discarded.
If a multicast forwarding boundary has been configured through the multicast
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boundary command, any multicast packet will be kept from crossing the
boundary.
Solution
1 Use the display pim routing-table command to check whether the
corresponding (S, G) entries exist on the router. If so, the router has received the
multicast data; otherwise, the router has not received the data.
2 Enter the display multicast minimum-ttl command to check the configured
minimum TTL value required for multicast packets to be forwarded. Use the undo
multicast minimum-ttl command on the concerned interfaces to restore the
required minimum TTL value to the system default, or configure multicast packets
to be sent with a higher TTL value from the multicast source.
3 Use the display multicast boundary command to view the multicast boundary
information on the interfaces. Use the multicast boundary command to change
the multicast forwarding boundary setting.
4 In the case of PIM-SM, use the display current-configuration command to
check the BSR and RP information.
Troubleshooting Multicast Routing and Forwarding 1113