H3C Technologies H3C SecPath F1000-E - Manual (Page 150)

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• Because a hello message does not carry the PIM mode information, a router running PIM is unable
to know what PIM mode its PIM neighbor is running. If different PIM modes are enabled on the RPF
interface and on the corresponding interface of the RPF neighbor router, the establishment of a
multicast distribution tree will surely fail, causing abnormal multicast forwarding.
• The same PIM mode must run on the entire network. Otherwise, the establishment of a multicast
distribution tree will surely fail, causing abnormal multicast forwarding.
Solution
Step1 Check unicast routes. Use the display ip routing-table command to check whether a unicast route
exists from the receiver host to the multicast source.
Step2 Check that PIM is enabled on the interfaces, especially on the RPF interface. Use the display pim
interface command to view the PIM information on each interface. If PIM is not enabled on the
interface, use the pim dm or pim sm command to enable PIM-DM or PIM-SM.
Step3 Check that the RPF neighbor is a PIM neighbor. Use the display pim neighbor command to view the
PIM neighbor information.
Step4 Check that PIM and IGMP are enabled on the interfaces directly connecting to the multicast source and
to the receivers.
Step5 Check that the same PIM mode is enabled on related interfaces. Use the display pim interface
verbose command to check whether the same PIM mode is enabled on the RPF interface and the
corresponding interface of the RPF neighbor router.
Step6 Check that the same PIM mode is enabled on all the routers in the entire network. Make sure that the
same PIM mode is enabled on all the routers: PIM-SM on all routers, or PIM-DM on all routers. In the case
of PIM-SM, also check that the BSR and RP configurations are correct.
Multicast Data Abnormally Terminated on an Intermediate
Router
Symptom
An intermediate router can receive multicast data successfully, but the data cannot reach the last hop
router. An interface on the intermediate router receives data but no corresponding (S, G) entry is created
in the PIM routing table.
Analysis
• When a router receives a multicast packet, it decrements the TTL value of the 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 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 packets. If the multicast
data fails to pass the ACL rule defined in this command, PIM cannot create the route entry, either.