3Com Switch 8800 Advanced Software V5 Configuration Guide

620 CHAPTER 43: MSDP CONFIGURATION
■ ACL as an SA message creation rule
■ ACL as a filtering rule for receiving or forwarding SA messages
■ Minimum TTL value of multicast packets encapsulated in SA messages
■ Maximum SA message cache size
Configuring SA Message
Content
Some multicast sources send multicast data at an interval longer than the aging
time of (S, G) entries. In this case, the source-side DR has to encapsulate multicast
data packet by packet in register messages and send them to the source-side RP.
The source-side RP transmits the (S, G) information to the remote RP through SA
messages. Then the remote RP joins the source-side DR and builds an SPT. Since
the (S, G) entries have timed out, remote receivers can never receive the multicast
data from the multicast source.
If the source-side RP is enabled to encapsulate register messages in SA messages,
when there is a multicast packet to deliver, the source-side RP encapsulates a
register message containing the multicast packet in an SA message and sends it
out. After receiving the SA message, the remote RP decapsulates the SA message
and delivers the multicast data contained in the register message to the receivers
along the RPT.
The MSDP peers deliver SA messages to one another. Upon receiving an SA
message, a device performs RPF check on the message. If the device finds that the
remote RP address is the same as the local RP address, it will discard the SA
message. In the Anycast RP application, however, you need to configure RPs with
the same IP address on two or more devices in the same PIM-SM domain, and
configure these devices as MSDP peers to one another. Therefore, a logic RP
address (namely the RP address on the logic interface) that is different from the
actual RP address must be designated for SA messages so that the messages can
pass the RPF check.
Follow these steps to configure the SA message content:
Configuring SA Request
Messages
By default, upon receiving a new Join message, a device does not send an SA
request message to its designated MSDP peer; instead, it waits for the next SA
message from its MSDP peer. This will cause the receiver to delay obtaining
multicast source information. To enable a new receiver to get the currently active
multicast source information as early as possible, you can configure devices to
send SA request messages to the designated MSDP peers upon receiving a Join
message of a new receiver.
Follow these steps to configure SA message transmission and filtering:
To do... Use the command... Remarks
Enter system view system-view -
Enter MSDP view msdp -
Enable encapsulation of a
registration message
encap-data-enable Optional
Disabled by default
Configure the interface
address as the RP address in
SA messages
originating-rp interface-type
interface-number
Optional
PIM RP address by default