Fault Symptom
On the network, there are 108 channels, Router A functions as the RP, and Router C functions as the receiver's DR. Router B and Router C are connected through two links among which load balancing is carried out. Router A and Router B are connected through three links among which load balancing is carried out.
Ten channels are lost on Router C, and users cannot watch the programs of these channels. Users can normally watch the programs of the other 98 channels.
Fault Analysis
1. Run the display pim routing-table command on Router A, Router B, and Router C in sequence to check the PIM routing table. You can find that there are 98 (S, G) entries on each device, and 10 (S, G) entries are lost, which is consistent with the fault symptom. There are 108 (*, G) entries on only Router C, and Router A and Router B do not have any (*, G) entry.
Because the two devices do not generate any (*, G) entry, the two devices cannot generate any (S, G) entry, and multicast channels are lost. It is primarily concluded that the fault occurs on Router B.
2. Run the debugging pim join-prune command on Router B to view the debugging of Join messages. You can find that all Join messages are discarded, because the RP address is invalid or the RP is unreachable.
<HUAWEI> debugging pim join-prune
*6.365990474 PE_OUJDA_01_CEX PIM/7/JP:(public net): PIM-SM: Invalid RP-address or RP not found, Ignoring (*,239.255.0.151) join received on GigabitEthernet4/0/0.3 (S12300)
*6.365990475 PE_OUJDA_01_CEX PIM/7/JP:(public net): PIM-SM: Invalid RP-address or RP not found, Ignoring (*,239.255.0.150) join received on GigabitEthernet4/0/0.3 (S12300)
3. On Router B, check the reachability of the RP. Run the pim command to enter the PIM view. Then, run the display this command in the PIM view to identify the IP address of the RP.
<HUAWEI> system-view
[HUAWEI] pim
[HUAWEI-pim] display this
#
pim
static-rp 196.217.250.111
#
return
The RP is statically configured, and the IP address of the RP is 196.217.250.111. There are three links among which load balancing is carried between Router B and the RP. The outbound interfaces of the links are GE 1/0/1, GE 1/0/2, POS 2/0/0 respectively. Check the RPF interface, and you can find that the RPF interface is POS 2/0/0. POS 2/0/0, however, is not configured with PIM-SM, which causes the RP to be unreachable for PIM-SM. As a result, all Join messages are discarded, and are not sent to Router A.
<HUAWEI> display multicast rpf-info 196.217.250.111
VPN-Instance: public net
RPF information about source: 196.217.250.111
RPF interface: POS 2/0/0
Referenced route/mask: 196.217.250.111/32
Referenced route type: unicast
Route selection rule: preference-preferred
Load splitting rule: disable
You can use either of the following methods to rectify the fault:
· Enable PIM-SM on POS 2/0/0.
· Configure a multicast static route on GE 1/0/0 and set GE 1/0/0 as the outbound interface of the multicast static route.
In this case, the second method is used to rectify the fault.
Procedure
1. Run the interface interface-type interface-number command on Router B to enter the interface view.
2. Run the ip rpf-route-static source-address protocol process-id rpf- br command to configure the interface as the RPF interface.
Summary
Multicast forwarding depends on unicast routes. PIM needs to be configured on the nodes along the path from the multicast source to a receiver. In the case of load balancing, PIM or a multicast static route needs to be configured on the nodes along each path.
