3Com Switch 8800 Advanced Software V5 Configuration Guide

Configuring BGP Routing Attributes 441
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CAUTION:
■ Using a routing policy can set a preference for routes meeting its filtering
conditions. Routes not meeting the conditions use the default preference.
■ If other conditions are identical, the route with the smallest MED value is
selected as the best external route of the AS.
■ Using the peer next-hop-local command can specify the router as the next
hop for a peer/peer group. If BGP load balancing is configured, the router
specify itself as the next hop for routes to a peer/peer group regardless of
whether the peer next-hop-local command is configured.
■ In a "third party next hop" network, that is , the two EBGP peers reside in a
common broadcast subnet, the BGP router does not specify itself as the next
hop for routes to the EBGP peer, unless the peer next-hop-local command is
configured.
■ In general, BGP checks whether the AS_PATH attribute of a route from a peer
contains the local AS number. If so, it discards the route to avoid routing loops.
Specify the router as the next hop of
routes to a peer/peer group
peer { group-name |
ip-address }
next-hop-local
Optional
By default, routes to an
EBGP peer/peer group
take the router as the next
hop, while routes to an
IBGP peer/peer group do
not take the local router as
the next hop.
Configure the
AS_PATH attribute
Configure
repeating times of
local AS number in
routes from a
peer/peer group
peer { group-name |
ip-address }
allow-as-loop [
number ]
Optional
The local AS number can
not be repeated in routes
from the peer/peer group.
Disable the router
from taking
AS_PATH as a
factor for best
route selection
bestroute
as-path-neglect
Optional
By default, the router
takes AS_PATH as a factor
for best route selection
Specify a fake AS
number for a
peer/peer group
peer { group-name |
ip-address } fake-as
as-number
Optional
Not specified by default
This command is only
applicable to an EBGP peer
or peer group.
Substitute local AS
number for the AS
number of a
peer/peer group in
the AS_PATH
attribute
peer { group-name |
ip-address }
substitute-as
Optional
The substitution is not
configured by default.
Configure to not
keep private AS
number in
AS_PATH of
updates to a
peer/peer group
peer { group-name |
ip-address }
public-as-only
Optional
By default, BGP updates
carry private AS number.
To do... Use the command... Remarks