3Com Switch 7750 Configuration Guide Guide

348 CHAPTER 36: BGP CONFIGURATION
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CAUTION:
■ Using routing policy, you can configure the preference for the routes that
match the filtering conditions. As for the unmatched routes, the default
preference is adopted.
■ If other conditions are the same, the route with the lowest MED value is
preferred to be the exterior route of the AS.
■ After BGP load balance is configured, no matter whether the peer
next-hop-local command is executed or not, the local router changes the next
hop IP address to its own IP address before advertising a route to its IBGP
peers/peer group.
Adjusting and
Optimizing a BGP
Network
Adjusting and optimizing BGP network involves the following aspects:
1 BGP clock
BGP peers send Keepalive messages to each other periodically through the
connections between them to make sure the connections operate properly. If a
router does not receive the Keepalive or any other message from its peer in a
specific period (know as Holdtime), the router considers the BGP connection
operates improperly and thus disconnects the BGP connection.
When establishing a BGP connection, the two routers negotiate for the Holdtime
by comparing their Holdtime values and take the smaller one as the Holdtime.
2 Limiting the number of route prefixes to be received from the peer/peer group
By limiting the number of route prefixes to be received from the specified
peer/peer group, you can control the size of the local routing table, thus
optimizing the performance of local router system and protecting local routers.
When the number of route prefixes received exceeds the configured value, a
router enabled with this function is automatically disconnected from the peer/peer
group.
3 BGP connection reset
To make a new BGP routing policy taking effect, you need to reset the BGP
connection. This temporarily disconnects the BGP connection. In Comware
Configure the AS_Path attribute
peer { group-name |
ip-address } allow-as-loop
[ number ]
Optional
By default, the number of
local AS number
occurrences allowed is 1.
peer group-name
as-number as-number
Optional
By default, the local AS
number is not assigned to
a peer group.
peer group-name
public-as-only
Optional
By default, a BGP update
packet carries the private
AS number.
Table 282 Configure BGP route attributes
Operation Command Description