3Com Router User Manual

OSPF Configuration Example447
dial-up mode, although the PPP protocol is encapsulated on the link layer, it is 
still NBMA type. The peer must be specified manually. Use the 
ospf peer 
ip-address command.
■If the network type is broadcast network or NBMA, at least the priority of one 
interface must be over 0.
■If an area is configured to a stub area, all routers connected with this area must 
be configured to stub areas. 
■The interface type of two adjacent routers must be the same.
■If two or more...

448CHAPTER 29: CONFIGURING OSPF 

30
CONFIGURING BGP
This chapter covers the following topics:
■BGP Overview
■Configuring BGP 
■Displaying and Debugging BGP 
■BGP Configuration Example
BGP OverviewBorder Gateway Protocol (BGP) is an inter-AS dynamic route discovery protocol. Its 
primary function is to exchange loop-free routing information between ASs 
automatically and to construct the topology diagram of an AS through the 
exchange of path reachability information, including AS numbers. It constructs the 
topological diagrams of the...

450CHAPTER 30: CONFIGURING BGP
The BGP system runs on a specific router as a high layer protocol. At system 
startup, the whole BGP routing table is transmitted for the exchange of routing 
information. Later on, only an update message is transmitted for updating the 
routing table. In the system, keep-alive messages are received and transmitted to 
check whether the connection between routers is normal.
The router transmitting the BGP message is called the BGP speaker. It receives and 
generates new...

Configuring BGP 451
■Configuring a BGP Community
■Configuring a BGP AS Confederation Attribute
■Configuring Route Dampening
■Configuring Synchronization of BGP and IGP
■Configuring the Interactions between BGP and an IGP 
■Defining an Access List Entry, an AS Path-list Entry, a Routing Policy
■Configuring a Route Filter for BGP
■Resetting BGP Connections
Enabling BGPSpecify the local AS number when BGP is enabled. After BGP is enabled, the local 
router continuously monitors whether any incoming BGP...

452CHAPTER 30: CONFIGURING BGP
BGP peer advanced configuration includes the following steps:
1Configure the connection between EBGP peers that are connected indirectly.
Ta b l e 511   Configure Connection Between EBGP Peers Connected Indirectly
By default, the BGP connection can be established with a directly connected peer 
router.
2Configure the BGP version of the peer.
Ta b l e 512   Configure the BGP Version of the Peer
By default, software accepts BGP Version 4.
3Set the timers for the BGP peer.
Ta...

Configuring BGP 453
Ta b l e 515   Configure to Send Community Attribute to the Peer
By default, the community attributes are not sent to the peer.
6Configure the peer to be the client of the route reflector. 
Ta b l e 516   Configure the Peer to be the Client of the Route Reflector
7Configure to distribute default route to the peer.
Ta b l e 517   Configure to Distribute Default Router to the Peer
By default, the local router does not advertise the default route to any peer. A next 
hop should be sent...

454CHAPTER 30: CONFIGURING BGP
By default, the route from the peer or peer group is not designated with any route 
policy.
10Create an filtering policy based on access list for the peer.
Ta b l e 520   Create a Fltering Policy Based on Access List for the Peer
By default, no route filtering policy based on IP ACL for a peer is set.
11Create BGP route filtering based on the AS path for the peer. By default, a BGP 
filter is disabled.
Ta b l e 521   Create a BGP Route Filtering Based on AS Path for the...

Configuring BGP 455
By default, MED values from different AS neighboring routes are not compared 
when determining the best route.
This configuration should not be used unless it is certain that different ASs uses 
the same IGP and routing modes.
Configuring the Local 
PreferenceConfiguring different local preferences affects BGP routing selection. When a 
router running BGP gets routes with the same destination address but different 
next hops through different internal peers, it selects the route of...

456CHAPTER 30: CONFIGURING BGP
holdtime-interval attribute is 180 seconds and may have a time interval 
ranging from 3 to 42949675 seconds.
Configuring a BGP Peer 
GroupThe BGP peer group command can be used for user configuration. When starting 
several peers of the same configuration, you can first create and configure one 
peer group, then add other peer groups into this group to get the same 
configuration. 
Configuring a basic BGP peer group includes creating a peer group and adding a 
peer to the...