3com 3031 Instruccion De Instalación

C

HAPTER

 42: BGP C

ONFIGURATION

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If the Ping operation succeeds, check if there is an ACL denying TCP port 179.If 
the ACL is configured, cancel the denying of port 179.

As described at the beginning of this chapter, BGP, as the practical exterior 
gateway protocol, is widely used in interconnection between autonomous 
systems. The traditional BGP-4 can only manage the routing information of IPv4 
and has limitation in inter-AS routing when used in the application of other 
network layer protocols (such as IPv6 etc).

In order to support multiple network layer protocols, IETF extended BGP-4 and 
formed MBGP (Multiprotocol Extensions for BGP-4, multiple protocols extension 
of BGP-4). The present MBGP standard is RFC2858.

MBGP is compatible, that is, a router supporting BGP extension can be 
interconnected with a router that does not support it.

In the packets BGP-4 uses, three pieces of information related to IPv4 are carried in 
the update packet. They are NLRI (Network Layer Reachability Information), 
Next_Hop (The next hop address) in path attribute and Aggregator in path 
attribute (This attribute includes the BGP speaker address which forms the 
summary route).

The BGP speaker running on the Internet usually has an IPv4 address. Therefore, it 
is only necessary for BGP-4 to reflect the information of the specified network 
layer protocol to NLRI and the Next_Hop in the route attribute to implement 
supporting to multiple network layer protocols.

Two new path attributes are imported into MBGP:

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MP_REACH_NLRI: Multiprotocol Reachable NLRI. It is used to advertise 
reachable routes and next-hop information.

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MP_UNREACH_NLRI: Multiprotocol Unreachable NLRI. It is used to remove 
unreachable routes.

These two attributes are optional non-transitive. Therefore, the BGP speaker that 
does not provide multiple protocols ability will ignore the information of them nor 
transfer them to other peers.

The router adopts address family to differentiate different network layer protocols. 
For values of address family, refer to RFC1700.

The router provides various MBGP extended applications including extension of 
multicast and BGP/MPLS VPN etc. Different extended applications should be 
performed in their own address family views.

For MBGP applied in multicast, refer to Chapter 50 “MBGP Multicast Extension 
Configuration”. For MBGP applied in BGP/MPLS VPN, refer to Chapter 54 
“BGP/MPLS VPN Configuration”.