Rps Unable To Join Spt In Pim-Sm - 3Com MSR 50 Series Configuration Manual

RPs Unable to Join SPT in
PIM-SM
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, and therefore no routing entry can be created in the PIM routing
table.
In addition, the source-policy command is used to filter received multicast
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packets. If the multicast data fails to pass the ACL rule defined in this
command, PIM cannot create the route entry, either.
Solution
1 Check the minimum TTL value for multicast forwarding. Use the display
current-configuration command to check the minimum TTL value for multicast
forwarding. Increase the TTL value or remove the multicast minimum-ttl
command configured on the interface.
2 Check the multicast forwarding boundary configuration. Use the display
current-configuration command to check the multicast forwarding boundary
settings. Use the multicast boundary command to change the multicast
forwarding boundary settings.
3 Check the multicast filter configuration. Use the display current-configuration
command to check the multicast filter configuration. Change the ACL rule defined
in the source-policy command so that the source/group address of the multicast
data can pass ACL filtering.
Symptom
An RPT cannot be established correctly, or the RPs cannot join the SPT to the
multicast source.
Analysis
As the core of a PIM-SM domain, the RPs serve specific multicast groups.
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Multiple RPs can coexist in a network. Make sure that the RP information on all
routers is exactly the same, and a specific group is mapped to the same RP.
Otherwise, multicast forwarding will fail.
If the static RP mechanism is used, the same static RP command must be
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executed on all the routers in the entire network. Otherwise, multicast
forwarding will fail.
Solution
1 Check that a route is available to the RP. Carry out the display ip routing-table
command to check whether a route is available on each router to the RP.
2 Check the dynamic RP information. Use the display pim rp-info command to
check whether the RP information is consistent on all routers.
Troubleshooting PIM Configuration 1207