Motorola BSR 2000, Configuration And Management Manual

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Release 1.0 Configuring BGP
526360-001-00 Rev. B MGBI 12-37
Assigning an Interface to BGP Session
The neighbor update-source command is used to allow a BGP session to use any
operational interface for TCP connections by specifying an IP address or peer-group
and the proper interface. This feature is often used in conjunction with loopback
interfaces. Loopback interfaces are often used by IBGP peers. The advantage of using
loopback interfaces is that they eliminate operational status and negotiated address
dependencies that result from using the IP address of a physical interface on the router
to configure BGP. Loopback interfaces are rarely used between EBGP peers because
they are usually directly connected and depend on a specific interface for
connectivity.
Use the neighbor update-source loopback command in Router Configuration mode
to assign a loopback interface to the BGP session:
MOT(config-bgp)#
neighbor {<
A.B.C.D
> | <
WORD
>} update-source loopback
<1-64
>
where:
A.B.C.D
is the IP address of the BGP neighbor.
WORD
is the name of the BGP peer group.
loopback indicates the interface type.
1-64
is the loopback interface number.
Example
Figure 12-12 shows a network that can benefit from the use of a loopback
interface, because an alternate path exists.
Routers New York and Albany are
running IBGP within AS 100. Router New York specifies the IP address of the
loopback interface (140.10.0.1) of Router Albany in the
neighbor remote-as
command. Router Albany is configured to include the neighbor update-source
command so that the source of BGP TCP connections for the specified neighbor is the
IP address of the loopback interface instead on the IP address of a physical interface.
This eliminates the dependency on the physical interface. If a cable break occurs on
S0, the connection can still be maintained via S1, provided IP connectivity still exists
to the loopback.
Note: The loopback interface is unrelated to the IP loopback address
127.x.x.x.