3Com MSR 50 Series, Configuration Manual

Page: 842 / 2443

842 C
HAPTER
56: BGP C
ONFIGURATION
c
CAUTION:
■
It is required to specify for a BGP router a router ID, a 32-bit unsigned integer
and the unique identifier of the router in the AS.
■
You can specify a router ID manually. If not, the system selects an IP address as
the router ID. The selection sequence is the highest IP address among loopback
interface addresses; if not available, then the highest IP address of interfaces. It
is recommended to specify a loopback interface address as the router ID to
enhance network reliability. Only when the interface with the selected Router
ID or the manual Router ID is deleted will the system select another ID for the
router.
■
You need to create a peer group before configuring it. Refer to “Configuring
BGP Peer Groups” on page 851 for creating a peer group.
■
To establish multiple BGP connections between two devices, you need to
specify on the local router the respective source interfaces for establishing TCP
connections to the peers on the peering BGP router; otherwise, the local BGP
router may fail to establish TCP connections to the peers when using the
outbound interfaces of the best routes as the source interfaces.
■
In general, direct physical links should be available between EBGP peers. If not,
you can use the
peer ebgp-max-hop command to establish a TCP connection
over multiple hops between two peers. You need not use this command for
directly connected EBGP peers, which employ loopback interfaces for peer
relationship establishment.
■
If you both reference a routing policy and use the peer { group-name |
ip-address } preferred-value value command to set a preferred value for
routes from a peer, the routing policy sets a non-zero preferred value for routes
matching it. Other routes not matching the routing policy uses the value set
with the command. If the preferred value in the routing policy is zero, the
routes matching it will also use the value set with the command. For
information about using a routing policy to set a preferred value, refer to the
command
peer { group-name | ip-address } route-policy route-policy-name
{ export | import } in this document, and the command apply
preferred-value preferred-value in “Routing Policy Configuration” on page
991 .
Specify the source interface
for establishing TCP
connections to a peer or peer
group peer { group-name |
ip-address }
connect-interface
interface-type
interface-number
Optional
By default, BGP uses the
outbound interface of the best
route to the BGP peer as the
source interface for establishing
a TCP connection.
Allow the establishment of
EBGP connection to a non
directly connected peer/peer
group peer { group-name |
ip-address } ebgp-max-hop
[ hop-count ]
Optional
Not allowed by default. By
specifying
hop-count, you can
specify the max hops for the
EBGP connection
To do... Use the command... Remarks