c-bsr (IPv4)
Function
The c-bsr command configures a C-BSR.
The undo c-bsr command restores the default configuration.
Parameters
| Parameter | Description | Value |
|---|---|---|
| interface-type interface-number | Specifies the type and the number of a FW interface. C-BSR is configured on this interface. PIM-SM must be enabled on this interface to make the configuration effective. | - |
| hash-length | Specifies the hash mask length of the C-BSR. The mask is used in a hash function to calculate the RP. | The value is an integer that ranges from 0 to 32. By default, the value is 30. |
| priority | Specifies a priority of the C-BSR. The greater the value is, the higher the priority of the C-BSR is. | It is an integer that ranges from 0 to 255. By default, it is 0. |
Usage Guidelines
By default, the C-BSR is not configured.
Usage Scenario
In a PIM-SM network, the Rendezvous Point (RP) is dynamically elected through the BootStrap router (BSR) mechanism. The BSR collects a lot of Candidate-Rendezvous Point (C-RP) information or receives auto-RP advertisement messages from other FW, and then advertises the RP-set to the entire network. All FW in the network can then calculate the RP to which a specific group corresponds according to the RP-set. Since the BSR and other devices in a PIM-SM domain need to exchange a great deal of information, a lot of bandwidth should be reserved between the C-BSR and other devices in the PIM-SM domain.
A FW can act as the C-RP and C-BSR at the same time. Multiple instance can exist on a FW. A maximum of one C-BSR can be configured in each instance. If you run the c-bsr command in an instance repeatedly, only the latest one is valid.
In a PIM-SM domain, configure one or more C-BSRs. A BSR is automatically elected among C-BSRs. The BSR collects and advertises the RP information.
The C-BSR should be FW of the backbone network. When configuring a FW as a C-BSR, specify an interface enabled with PIM-SM. The following briefly describes the automatic election of the BSR among C-BSRs:
They use the IP address of the interface specified with the c-bsr command as the BSR address to send Bootstrap messages.
When a C-BSR receives a Bootstrap message from other FW, it compares the BSR in the received Bootstrap message with the current BSR. The compared items are priorities and IP addresses. If the two BSRs have the same priority, the BSR with a larger IP address is preferred. If the BSR carried in the Bootstrap message is better than the current BSR, the C-BSR replaces its BSR address with the address of the BSR in received message. Otherwise, the C-BSR keeps its BSR address and continues to consider itself as the BSR.
Prerequisites
The interface that acts as C-BSR must be enabled with PIM-SM.
Configure static routes for BSR messages learned by a GRE tunnel to ensure that the next hop to the BSR is a Generic Routing Encapsulation (GRE) interface. The configuration of multicast static routes needs to be properly planned to avoid routing loops.