3Com MSR 50 Series Configuration Manual page 848

848 C 56: BGP C
HAPTER ONFIGURATION
c
To do...
Configure the AS_PATH
attribute
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.
You can specify a fake AS number to hide the real one as needed. The fake AS
■
number applies to EBGP peers only, that is, EBGP peers in other ASs can only
find the fake AS number.
Use the command...
Configure peer { group-name |
repeating times ip-address }
of local AS allow-as-loop
number in routes [ number ]
from a peer/peer
group
Disable the bestroute
router from as-path-neglect
taking AS_PATH
as a factor for
best route
selection
Specify a fake AS peer { group-name |
number for a ip-address } fake-as
peer/peer group as-number
Substitute local peer { group-name |
AS number for ip-address }
the AS number substitute-as
of a peer/peer
group in the
AS_PATH
attribute
Configure to not peer { group-name |
keep private AS ip-address }
number in public-as-only
AS_PATH of
updates to a
peer/peer group
Remarks
Optional
The local AS
number can not be
repeated in routes
from the peer/peer
group.
Optional
By default, the
router takes
AS_PATH as a
factor for best
route selection
Optional
Not specified by
default
This command is
only applicable to
an EBGP peer or
peer group.
Optional
The substitution is
not configured by
default.
Optional
By default, BGP
updates carry
private AS number.