BGP path selection configuration example

As shown in Figure 75, all switches run BGP.

• EBGP runs between Switch A and Switch B, and between Switch A and Switch C.

• IBGP runs between Switch B and Switch D, and between Switch D and Switch C. OSPF is the IGP protocol in AS 200.

Configure routing policies, making Switch D use the route 1.0.0.0/8 from Switch C as the optimal.

1. Configure IP addresses for interfaces. (Details not shown.)

2. Configure OSPF on Switch B, Switch C, and Switch D:

   # Configure Switch B.

   <SwitchB> system-view
   [SwitchB] ospf
   [SwitchB-ospf] area 0
   [SwitchB-ospf-1-area-0.0.0.0] network 192.1.1.0 0.0.0.255
   [SwitchB-ospf-1-area-0.0.0.0] network 194.1.1.0 0.0.0.255
   [SwitchB-ospf-1-area-0.0.0.0] quit
   [SwitchB-ospf-1] quit
   

   # Configure Switch C.

   <SwitchC> system-view
   [SwitchC] ospf
   [SwitchC-ospf] area 0
   [SwitchC-ospf-1-area-0.0.0.0] network 193.1.1.0 0.0.0.255
   [SwitchC-ospf-1-area-0.0.0.0] network 195.1.1.0 0.0.0.255
   [SwitchC-ospf-1-area-0.0.0.0] quit
   [SwitchC-ospf-1] quit
   

   # Configure Switch D.

   <SwitchD> system-view
   [SwitchD] ospf
   [SwitchD-ospf] area 0
   [SwitchD-ospf-1-area-0.0.0.0] network 194.1.1.0 0.0.0.255
   [SwitchD-ospf-1-area-0.0.0.0] network 195.1.1.0 0.0.0.255
   [SwitchD-ospf-1-area-0.0.0.0] quit
   [SwitchD-ospf-1] quit
   

3. Configure BGP connections:

   # Configure Switch A.

   <SwitchA> system-view
   [SwitchA] bgp 100
   [SwitchA-bgp-default] peer 192.1.1.2 as-number 200
   [SwitchA-bgp-default] peer 193.1.1.2 as-number 200
   [SwitchA-bgp-default] address-family ipv4 unicast
   [SwitchA-bgp-default-ipv4] peer 192.1.1.2 enable
   [SwitchA-bgp-default-ipv4] peer 193.1.1.2 enable
   

   # Inject network 1.0.0.0/8 to the BGP routing table on Switch A.

   [SwitchA-bgp-default-ipv4] network 1.0.0.0 8
   [SwitchA-bgp-default-ipv4] quit
   [SwitchA-bgp-default] quit
   

   # Configure Switch B.

   [SwitchB] bgp 200
   [SwitchB-bgp-default] peer 192.1.1.1 as-number 100
   [SwitchB-bgp-default] peer 194.1.1.1 as-number 200
   [SwitchB-bgp-default] address-family ipv4 unicast
   [SwitchB-bgp-default-ipv4] peer 192.1.1.1 enable
   [SwitchB-bgp-default-ipv4] peer 194.1.1.1 enable
   [SwitchB-bgp-default-ipv4] quit
   [SwitchB-bgp-default] quit
   

   # Configure Switch C.

   [SwitchC] bgp 200
   [SwitchC-bgp-default] peer 193.1.1.1 as-number 100
   [SwitchC-bgp-default] peer 195.1.1.1 as-number 200
   [SwitchC-bgp-default] address-family ipv4 unicast
   [SwitchC-bgp-default-ipv4] peer 193.1.1.1 enable
   [SwitchC-bgp-default-ipv4] peer 195.1.1.1 enable
   [SwitchC-bgp-default-ipv4] quit
   [SwitchC-bgp-default] quit
   

   # Configure Switch D.

   [SwitchD] bgp 200
   [SwitchD-bgp-default] peer 194.1.1.2 as-number 200
   [SwitchD-bgp-default] peer 195.1.1.2 as-number 200
   [SwitchD-bgp-default] address-family ipv4 unicast
   [SwitchD-bgp-default-ipv4] peer 194.1.1.2 enable
   [SwitchD-bgp-default-ipv4] peer 195.1.1.2 enable
   [SwitchD-bgp-default-ipv4] quit
   [SwitchD-bgp-default] quit
   

4. Configure local preference for route 1.0.0.0/8, making Switch D give priority to the route learned from Switch C:

   # Define IPv4 basic ACL 2000 on Switch C to permit route 1.0.0.0/8.

   [SwitchC] acl basic 2000
   [SwitchC-acl-ipv4-basic-2000] rule permit source 1.0.0.0 0.255.255.255
   [SwitchC-acl-ipv4-basic-2000] quit
   

   # Configure a routing policy named localpref on Switch C, setting the local preference of route 1.0.0.0/8 to 200 (the default is 100).

   [SwitchC] route-policy localpref permit node 10
   [SwitchC-route-policy-localpref-10] if-match ip address acl 2000
   [SwitchC-route-policy-localpref-10] apply local-preference 200
   [SwitchC-route-policy-localpref-10] quit
   

   # Apply routing policy localpref to routes from peer 193.1.1.1.

   [SwitchC] bgp 200
   [SwitchC-bgp-default] address-family ipv4 unicast
   [SwitchC-bgp-default-ipv4] peer 193.1.1.1 route-policy localpref import
   [SwitchC-bgp-default-ipv4] quit
   [SwitchC-bgp-default] quit
   

   # Display the BGP routing table on Switch D.

   [SwitchD] display bgp routing-table ipv4
   
    Total number of routes: 2
   
    BGP local router ID is 195.1.1.1
    Status codes: * - valid, > - best, d - dampened, h - history,
                  s - suppressed, S - stale, i - internal, e - external
                  Origin: i - IGP, e - EGP, ? - incomplete
   
        Network            NextHop         MED        LocPrf     PrefVal Path/Ogn
   
   * >i 1.0.0.0            193.1.1.1                  200        0       100i
   *  i                    192.1.1.1                  100        0       100i
   

   Route 1.0.0.0/8 learned from Switch C is the optimal.