Mesh Group
Background
- Source active (SA) messages are flooded between peers. Especially when many MSDP peers are configured in the same PIM-SM domain, reverse path forwarding (RPF) rules cannot filter out useless SA messages effectively. The MSDP peer needs to perform the RPF check on each received SA messages, which brings heavy workload to the system.
- SA messages are discarded due to RPF check failures.
To resolve these problems, configure a mesh group.
Implementation Principle
A mesh group requires each two MSDP peers in the group to set up a peer relationship, implementing full-mesh connections in the group. To implement the mesh group function, add all MSDP peers in the same and different ASs to the same mesh group on a multicast device. When a member of the mesh group receives an SA message, it checks the source of the SA message:
If the SA message is sent by a member of the mesh group, the member directly accepts the message without performing the RPF check. In addition, it does not forward the message to other members in the mesh group.
In real-world situations, adding all MSDP peers in the same and different ASs to the same mesh group is recommended to prevent SA messages from being discarded due to RPF check failures.
If the SA message is sent by an MSDP peer outside the mesh group, the member performs the RPF check on the SA message. If the SA message passes the check, the member forwards it to other members of the mesh group.
The mesh group mechanism greatly reduces SA messages to be exchanged among MSDP peers, relieving the workload of the multicast device.
An MSDP peer can belong to only one mesh group.