3com S7906E Manuel De Montage
1-61
Origin : i - IGP, e - EGP, ? - incomplete
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 9.1.1.0/24 10.1.3.1 0 100 0 100i
[SwitchD] display bgp routing-table 9.1.1.0
BGP local router ID : 4.4.4.4
Local AS number : 65001
Paths: 1 available, 1 best
BGP routing table entry information of 9.1.1.0/24:
From : 10.1.3.1 (1.1.1.1)
Relay Nexthop : 0.0.0.0
Original nexthop: 10.1.3.1
AS-path : 100
Origin : igp
Attribute value : MED 0, localpref 100, pref-val 0, pre 255
State : valid, internal, best,
Not advertised to any peers yet
The output information shows that:
z
Switch F can send route information to Switch B and Switch C through the confederation by
establishing only an eBGP connection with Switch A.
z
Switch B and Switch D are in the same confederation, but belong to different sub ASs. They obtain
external route information from Switch A and generate the same BGP route entries; it seems like
that they reside in the same AS although they have no direct connection in between.
BGP Path Selection Configuration
Network requirements
z
In the figure below, all switches run BGP. Between Switch A and Switch B, and between Switch A
and Switch C are eBGP connections. Between Switch B and Switch D, and between Switch D and
Switch C are iBGP connections.
z
OSPF is the IGP protocol in AS 200.
z
Configure routing policies, making Switch D use the route 1.0.0.0/8 from Switch C as the optimal.
Figure 1-26 Network diagram for BGP path selection configuration
Switch A
AS 100
Vlan-int101
Switch C
AS 200
Vlan-int200
Switch B
Switch D
Vlan-int100
Vlan-int200
Vlan-int400
Vlan-int400
Vlan-int300
Vlan-int300
Vlan-int100
Device
Interface
IP address
Device
Interface
IP address
Switch A
Vlan-int101
1.0.0.0/8
Switch D
Vlan-int400
195.1.1.1/24
Vlan-int100
192.1.1.1/24
Vlan-int300
194.1.1.1/24