Troubleshooting Ipv6 Pim; A Multicast Distribution Tree Cannot Be Correctly Built - HP MSR2003 Configuration Manual

Troubleshooting IPv6 PIM

A multicast distribution tree cannot be correctly built

Symptom
An IPv6 multicast distribution tree cannot be correctly built because no IPv6 multicast forwarding entries
are established on the routers (including routers directly connected with multicast sources or receivers) in
an IPv6 PIM network.
Analysis
• On an IPv6 PIM-DM network, IPv6 multicast data is flooded from the router that directly connects to
the IPv6 multicast source to the routers that directly connects to the receivers. When the IPv6
multicast data is flooded to a router, the router creates an (S, G) entry only if it has a route to the IPv6
multicast source. The router cannot create an (S, G) entry under either of the following conditions:
The router does not have a route to the IPv6 multicast source.
IPv6 PIM-DM is not enabled on the RPF interface toward the IPv6 multicast source.
On an IPv6 PIM-SM network, when a router wants to join the SPT, the router will create an (S, G)
•
entry only if it has a route to the IPv6 multicast source. The router cannot create an (S, G) entry under
either of the following conditions:
The router does not have a route to the IPv6 multicast source.
IPv6 PIM-SM is not enabled on the RPF interface toward the IPv6 multicast source.
When a multicast router receives an IPv6 multicast packet, it looks up the existing IPv6 unicast
•
routing table for the optimal route to the packet source. The outgoing interface of this route act as
the RPF interface and the next hop acts the RPF neighbor. The RPF interface completely relies on the
existing IPv6 unicast route and is independent of IPv6 PIM. The RPF interface must be enabled with
IPv6 PIM, and the RPF neighbor must be an IPv6 PIM neighbor. If IPv6 PIM is not enabled on the RPF
interface or the RPF neighbor, the multicast distribution tree cannot be correctly built, causing
abnormal multicast forwarding.
Because a hello message does not carry IPv6 PIM mode information, an IPv6 PIM router cannot
•
identify what IPv6 PIM mode its IPv6 PIM neighbor is running in. If the RPF interface on a router and
the connected interface of the router's RPF neighbor operate in different IPv6 PIM modes, the
multicast distribution tree cannot be correctly built. This causes abnormal multicast forwarding.
The same IPv6 PIM mode must run on the entire network. Otherwise, the multicast distribution tree
•
cannot be correctly built, causing abnormal multicast forwarding.
Solution
1. Use display ipv6 routing-table to verify that an IPv6 unicast route to the IPv6 multicast source or the
RP is available.
2. Use display ipv6 pim interface to verify IPv6 PIM information on each interface, especially on the
RPF interface. If IPv6 PIM is not enabled on the interfaces, use ipv6 pim dm or ipv6 pim sm to
enable IPv6 PIM-DM or IPv6 PIM-SM for the interfaces.
3. Use display ipv6 pim neighbor to verify that the RPF neighbor is an IPv6 PIM neighbor.
4. Verify that IPv6 PIM and MLD are enabled on the interfaces that directly connect to the IPv6
multicast sources or the receivers.
5. Use display ipv6 pim interface verbose to verify that the RPF interface on a router and the
connected interface of the router's RPF neighbor run the same IPv6 PIM mode.
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