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C

HAPTER

 46: MBGP M

ULTICAST

 E

XTENSION

 C

ONFIGURATION

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Send the routing information of a new reachable protocol.

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Send the next hop information about the new protocol with the same coding 
mode as that of NLRI.

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Enable the router to report part or all of the SNPAs (Sub-network Points of 
Attachment) saved in the local system.

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:

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AFI and SAFI.

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Withdrawn Routes: Contains one or multiple NLRIs, in which are the 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 runs on a router in the following two modes:

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IBGP (Internal BGP)

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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:

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Open Message: the first message sent after the TCP connection is established.

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Notification Message: error notification message.

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Keepalive Message: Message used to check the validity of the connection.

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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.

Basic configuration tasks of MBGP multicast extension include

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Enable MBGP multicast extension protocol

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Specify the network routes notified by the MBGP multicast extension

Advanced configuration tasks of MBGP multicast extension include

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Configure the MED value for an AS

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Compare MED values from different AS neighbor paths

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Configure local preference