Cannot see muticast traffic for group 232.X.X.X/24

Publication Date:  2014-10-31 Views:  682 Downloads:  0
Issue Description
1. Topology like below:


2. Group 232.X.X.X/24 is connected to S5700 and statci RP is configured on all Huawei switches. Customer finds that he could not receive multicast traffic from group 232.X.X.X/24
Alarm Information
None
Handling Process
1.Check the configuration based on the topology. Customer is using static RP and the configuration seems ok. RP information is correct.
2.Check the multicast group 232.X.X.X/24 and find it is SSM multicast group address range.
232.0.0.0/8 is SSM multicast group. By default, SSM multicast address does not need any RP
232.0.0.0-232.255.255.255 Default SSM group addresses that are valid on the entire network.
PIM-SM for SSM:
In the SSM model, user hosts know the exact positions of the multicast sources in advance. When user hosts join multicast groups, they can specify the sources from which they want to receive multicast data. The DR at the group member side then sends Join messages directly to the multicast sources. The Join message is transmitted upstream hop by hop to set up an SPT between the source and group members. The SSM model uses only part of the PIM-SM technology and IGMPv3. There is no need to maintain an RP, set up an RPT, or register a multicast source. As shown in Figure 2, HostA and HostB join a multicast group G. HostA needs to receive multicast data from S1, and HostB needs to receive multicast data from S2. The DRs at the group member side send Join messages to the multicast sources to set up SPTs.
Figure 2 Setting up an SPT in the SSM model
3.And customer configured 232.X.X.X/24 is in SSM multicast address group. Cannot configure static RP for SSM address. There are two solutions :
  • Please change 232.X.X.X to another no-SSM multicast address like 231.X.X.X
  • If customer must use it, we can create one SSM policy to deny these IP and then they will not be SSM multicast address.Run:
    pim
    The PIM view is displayed.
    Run:
    ssm-policy basic-acl-number      ///Create basic ACL and deny 232.X.X.X/24
Root Cause
232.0.0.0/8 is SSM multicast group. By default, SSM multicast address does not need any RP
Solution
There are two solutions :
1.Please change 232.X.X.X to another no-SSM multicast address like 231.X.X.X
2.If customer must use it, we can create one SSM policy to deny these IP and then they will not be SSM multicast address.Run:
pim
The PIM view is displayed.
Run:
ssm-policy basic-acl-number      ///Create basic ACL and deny 232.X.X.X/24
Suggestions
None

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