3Com Switch 8800 Family Configuration Guide

494 CHAPTER 46: MBGP MULTICAST EXTENSION CONFIGURATION
■ Send the routing information of a new reachable protocol.
■ Send the next hop information about the new protocol with the same coding
mode as that of NLRI.
■ Enable the router to report part or all of the SNPAs (Sub-network Points of
Attachment) saved in the local system.
MP_UNREACH_NLRI attribute
The MP_UNREACH_NLRI is an optional non-transitive attribute that can be used
for the purpose of withdrawing one or multiple unfeasible routes from service. It
includes the following fields:
■ AFI and SAFI.
■ Withdrawn Routes: Contains one or multiple NLRIs, in which are the
unreachable destination addresses.
An UPDATE packet that contains the MP_UNREACH_NLRI is not required to carry
any other path attributes.
These two attributes enables MBGP to carry multi-protocol information. MSGP
therefore supports both unicast and multicast by constructing different topology
maps to implement appropriate policies. Besides, MBGP may construct different
inter-domain routes for unicast and multicast under a same policy.
MBGP Operating Mode
and Message Type
MBGP runs on a router in the following two modes:
■ IBGP (Internal BGP)
■ EBGP (External BGP)
MBGP running in an autonomous system is called IBGP; MBGP running across
autonomous systems is called EBGP.
MBGP offers four types of messages:
■ Open Message: the first message sent after the TCP connection is established.
■ Notification Message: error notification message.
■ Keepalive Message: Message used to check the validity of the connection.
■ Update Message: the most important information in the MBGP system, used to
exchange routing information among peers. It consists of three parts at the
most: MP_UNREACH_NLRI, Path Attributes and MP_REACH_NLRI.
MBGP Multicast
Extension
Configuration
Basic configuration tasks of MBGP multicast extension include
■ Enable MBGP multicast extension protocol
■ Specify the network routes notified by the MBGP multicast extension
Advanced configuration tasks of MBGP multicast extension include
■ Configure the MED value for an AS
■ Compare MED values from different AS neighbor paths
■ Configure local preference