3Com Router User Manual

Configuring BGP 457
To configure an advanced BGP peer group configuration:
1Configure the AS number of BGP peer group
Ta b l e 528   Configure AS Number of BGP Peer Group
By default, there is no AS number for BGP peer group.
2Configure connection between peers indirectly connected
Ta b l e 529   Configure Connection Between Peers Indirectly Connected
By default, it only allows direct-connection peer.
The maximum hop value is ttl. The default value is 64, ranging from 1 to 255.
3Set the timers of BGP peer...

458CHAPTER 30: CONFIGURING BGP
By default, send no community attribute to any peer group.
6Configure a peer group as the client of a BGP reflector
In general, the AS requires that all the IBGP routers should be connected to one 
another, and the routes sent by the IBGP neighbors is not advertised, to prevent 
route loop. However, if the route reflector is used, not all IBGP speakers are 
required to be fully connected. This technique requires configuring an internal BGP 
peer as a router reflector. Other...

Configuring BGP 459
By default, the route from the peer or peer group is not designated with any route 
policy.
10Create a filtering policy based on the access list for the peer group
Ta b l e 537   Create a Filtering Policy Based on Access List for Peer Group
By default, no route filtering policy based on IP ACL for peer group is set.
11Create a BGP route filtering based on the AS path for the peer group
Ta b l e 538   Create a BGP Route Filtering Based on AS Path for Peer Group
By default, a BGP...

460CHAPTER 30: CONFIGURING BGP
By default, an aggregate is disabled.
Configure BGP Route 
ReflectorTo guarantee the connectivity between the IBGP peers, an all-closed network 
should exist between IBGP peers. In some networks, the internal BGP network can 
become very large (with more than one hundred sessions in each router), resulting 
in huge overhead. The route reflector designates a central router as the core of the 
internal sessions. Multiple BGP routers can become peers with this central router,...

Configuring BGP 461
The non-clients must form an all-closed network with the reflector, as they follow 
the basic rules of IBGP. A client should not be peer of other internal speakers 
outside its cluster. The reflecting function is achieved only on the route reflector. 
All the clients and non-clients are normal BGP peers irrelevant to the function. A 
client is a client only because the route reflector regards it as the client.
When the router reflector receives several routes to one destination, it...

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Ta b l e 542   Configure the Cluster ID
By default, the router ID of the route reflector is used as the cluster ID.
Configuring a BGP 
CommunityIn BGP range, a community is a logical area formed by a group of destinations 
which share common attributes for applying the route policy. A community is not 
limited to a network or an AS, and has no physical boundary.
The community attribute is an optional and transitional attribute. Some 
communities are commonly recognized and...

Configuring BGP 463
The disadvantage is that when a non-confederation scheme changes to a 
confederation scheme, it is required to reconfigure the router and to modify the 
logical topology. In addition, if the BGP strategy is not manually configured, the 
best path may not be selected through the confederation.
1Configure a Confederation
You can use different IGP for each sub-AS. Externally, a sub-AS is an integer and 
the confederation ID is the identification of the sub-AS.
Perform the following...

464CHAPTER 30: CONFIGURING BGP
Configuring Route 
DampeningRoute instability is frequently indicated when a route disappears that used to exist 
in the routing table. This route may reappear and disappear frequently, which is 
called routing flapping. When there is route flapping, the UPDATE and 
WITHDRAWN messages are broadcast repeatedly over the network, occupying 
bandwidth and processing time of the routers. The administrator should take 
action to prevent route flapping. Route dampening is a...

Configuring BGP 465
Ta b l e 547   Configure Route Dampening
By default, route dampening is disabled.
2Display route flap information.
Perform the following configurations in system view.
Ta b l e 548   Display Route Flap Information
Configuring 
Synchronization of BGP 
and IGPBGP protocol prescribes that a BGP router does not advertise the destination 
known through internal BGP peers to external peers unless the destination can be 
known also through IGP. If a router can know the destination through...

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peer and advertises it to other EBGP peers, it will try to check whether this 
destination can be reached through its AS.
Perform the following configurations in BGP view.
Ta b l e 549   Configure Synchronization of BGP and IGP
By default, BGP synchronizes with IGP.
3Com routers provide the ability to cancel BGP and IGP synchronization so the 
route from IBGP can be distributed without continuously checking if the IGP route 
still exists.
The synchronization of a border...