BGP path selection configuration example
Network requirements
In Figure 66, 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.
Figure 66: Network diagram
Device | Interface | IP address | Device | Interface | IP address |
Switch A | Vlan-int101 | 1.0.0.1/8 | Switch D | Vlan-int400 | 195.1.1.1/24 |
Vlan-int100 | 192.1.1.1/24 | Vlan-int300 | 194.1.1.1/24 | ||
Vlan-int200 | 193.1.1.1/24 | Switch C | Vlan-int400 | 195.1.1.2/24 | |
Switch B | Vlan-int100 | 192.1.1.2/24 | Vlan-int200 | 193.1.1.2/24 | |
Vlan-int300 | 194.1.1.2/24 |
Configuration procedure
Configure IP addresses for interfaces. (Details not shown.)
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
Configure BGP connections:
# Configure Switch A.
<SwitchA> system-view [SwitchA] bgp 100 [SwitchA-bgp] peer 192.1.1.2 as-number 200 [SwitchA-bgp] peer 193.1.1.2 as-number 200 [SwitchA-bgp] address-family ipv4 unicast [SwitchA-bgp-ipv4] peer 192.1.1.2 enable [SwitchA-bgp-ipv4] peer 193.1.1.2 enable
# Inject network 1.0.0.0/8 to the BGP routing table on Switch A.
[SwitchA-bgp-ipv4] network 1.0.0.0 8 [SwitchA-bgp-ipv4] quit [SwitchA-bgp] quit
# Configure Switch B.
[SwitchB] bgp 200 [SwitchB-bgp] peer 192.1.1.1 as-number 100 [SwitchB-bgp] peer 194.1.1.1 as-number 200 [SwitchB-bgp] address-family ipv4 unicast [SwitchB-bgp-ipv4] peer 192.1.1.1 enable [SwitchB-bgp-ipv4] peer 194.1.1.1 enable [SwitchB-bgp-ipv4] quit [SwitchB-bgp] quit
# Configure Switch C.
[SwitchC] bgp 200 [SwitchC-bgp] peer 193.1.1.1 as-number 100 [SwitchC-bgp] peer 195.1.1.1 as-number 200 [SwitchC-bgp] address-family ipv4 unicast [SwitchC-bgp-ipv4] peer 193.1.1.1 enable [SwitchC-bgp-ipv4] peer 195.1.1.1 enable [SwitchC-bgp-ipv4] quit [SwitchC-bgp] quit
# Configure Switch D.
[SwitchD] bgp 200 [SwitchD-bgp] peer 194.1.1.2 as-number 200 [SwitchD-bgp] peer 195.1.1.2 as-number 200 [SwitchD-bgp] address-family ipv4 unicast [SwitchD-bgp-ipv4] peer 194.1.1.2 enable [SwitchD-bgp-ipv4] peer 195.1.1.2 enable [SwitchD-bgp-ipv4] quit [SwitchD-bgp] quit
Configure attributes for route 1.0.0.0/8, making Switch D give priority to the route learned from Switch C:
(Method 1.) Configure a higher MED value for the route 1.0.0.0/8 advertised from Switch A to peer 192.1.1.2:
# Define an ACL numbered 2000 to permit route 1.0.0.0/8.
[SwitchA] acl number 2000 [SwitchA-acl-basic-2000] rule permit source 1.0.0.0 0.255.255.255 [SwitchA-acl-basic-2000] quit
# Define two routing policies, apply_med_50, which sets the MED for route 1.0.0.0/8 to 50, and apply_med_100, which sets the MED for route 1.0.0.0/8 to 100.
[SwitchA] route-policy apply_med_50 permit node 10 [SwitchA-route-policy-apply_med_50-10] if-match ip address acl 2000 [SwitchA-route-policy-apply_med_50-10] apply cost 50 [SwitchA-route-policy-apply_med_50-10] quit [SwitchA] route-policy apply_med_100 permit node 10 [SwitchA-route-policy-apply_med_100-10] if-match ip address acl 2000 [SwitchA-route-policy-apply_med_100-10] apply cost 100 [SwitchA-route-policy-apply_med_100-10] quit
# Apply routing policy apply_med_50 to the route advertised to peer 193.1.1.2 (Switch C), and apply_med_100 to the route advertised to peer 192.1.1.2 (Switch B).
[SwitchA] bgp 100 [SwitchA-bgp] address-family ipv4 unicast [SwitchA-bgp-ipv4] peer 193.1.1.2 route-policy apply_med_50 export [SwitchA-bgp-ipv4] peer 192.1.1.2 route-policy apply_med_100 export [SwitchA-bgp-ipv4] quit [SwitchA-bgp] 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 50 100 0 100i * i 192.1.1.1 100 100 0 100iRoute 1.0.0.0/8 is the optimal.
(Method 2.) Configure different local preferences on Switch B and C for route 1.0.0.0/8, making Switch D give priority to the route from Switch C:
# Define an ACL numbered 2000 on Switch C, permitting route 1.0.0.0/8.
[SwitchC] acl number 2000 [SwitchC-acl-basic-2000] rule permit source 1.0.0.0 0.255.255.255 [SwitchC-acl-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] address-family ipv4 unicast [SwitchC-bgp-ipv4] peer 193.1.1.1 route-policy localpref import [SwitchC-bgp-ipv4] quit [SwitchC-bgp] 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 100iRoute 1.0.0.0/8 learned from Switch C is the optimal.