Operation Manual – MBGPH3C S9500 Series Routing SwitchesChapter 1 MBGP Multicast ExtensionConfiguration1-2Among the information carried by MP_REACH_NLRI and MP_UNREACH_NLRI,address family identifier (AFI) and subsequent address family identifier (SAFI) canidentify the address family of the information. SAFI is a complement to network layerreachability information (NLRI), with the value 1 for the unicast mode of NLRI, and thevalue 2 for the multicast mode of NLRI.I. MP_REACH_NLRI attributeMP_REACH_NLRI is an optional non-transitive attribute, and can be used to:z Send the routing information of a new reachable protocol.z Send the next hop information about the new protocol with the same coding modeas that of NLRI.z Enable the router to report part or all of the sub-network points of attachment(SNPAs) saved in the local system.II. MP_UNREACH_NLRI attributeThe MP_UNREACH_NLRI is an optional non-transitive attribute that can be used forthe purpose of withdrawing one or multiple unfeasible routes. It includes the followingfields:z AFI and SAFI.z Withdrawn Routes: Contains one or multiple NLRIs, in which are the unreachabledestination addresses.An UPDATE packet that contains the MP_UNREACH_NLRI is not required to carry anyother path attributes.These two attributes enables MBGP to carry multi-protocol information. MBGPtherefore supports both unicast and multicast by constructing different topology mapsto implement appropriate policies. Besides, MBGP may construct different inter-domainroutes for unicast and multicast under a same policy.1.1.2 MBGP Operating Mode and Message TypeMBGP runs on a router in the following two modes:z Internal BGP (IBGP )z External BGP (EBGP )MBGP running in an autonomous system is called IBGP; MBGP running acrossautonomous systems is called EBGP.MBGP offers four types of messages:z Open Message: First message sent after the TCP connection is established.z Notification Message: Error notification message.z Keepalive Message: Message used to check the validity of the connection.
