Configuration procedure

Procedure
  1. Configure IP addresses for interfaces (omitted.)
  2. Configure OSPF on Switch B, C, and D.
  3. # Configure Switch B. 
    switch(config)# router ospf
switch(ospf)# area 0
switch(ospf)# network 192.1.1.0/ 0.0.0.255
switch(ospf)# network 194.1.1.0/ 0.0.0.255
switch(ospf)# exit
  4. # Configure Switch C. 
    switch(config)# router ospf
switch(ospf)# enable
switch(ospf)# area 0
switch(ospf)# network 193.1.1.0/ 0.0.0.255
switch(ospf)# network 195.1.1.0/ 0.0.0.255
switch(ospf)# exit
  5. # Configure Switch D. 
    switch(config)# router ospf
switch(ospf)# enable
switch(ospf)# area 0
switch(ospf)# network 194.1.1.0/ 0.0.0.255
switch(ospf)# network 195.1.1.0/ 0.0.0.255
switch(ospf)# exit
  6. Configure BGP connections.
  7. # Configure Switch A. 
    switch(config)# router bgp 100
switch(bgp)# neighbor 192.1.1.2 remote-as 200
switch(bgp)# neighbor 193.1.1.2 remote-as 200
  8. # Add network 1.0.0.0/8 to the BGP routing table on Switch A. 
    switch(bgp)# network 1.0.0.0/8
switch(bgp)# exit
  9. # Configure Switch B. 
    switch(config)# router bgp 200
switch(bgp)# neighbor 192.1.1.1 remote-as 100
switch(bgp)# neighbor 194.1.1.1 remote-as 200
switch(bgp)# exit
  10. # Configure Switch C. 
    switch(config)# router bgp 200
switch(bgp)# neighbor 193.1.1.1 remote-as 100
switch(bgp)# neighbor 195.1.1.1 remote-as 200
switch(bgp)# exit
  11. # Configure Switch D. 
    switch(config)# router bgp 200
switch(bgp)# neighbor 194.1.1.2 remote-as 200
switch(bgp)# neighbor 195.1.1.2 remote-as 200
switch(bgp)# exit
  12. Configure attributes for route 1.0.0.0/8, making Switch D give priority to the route learned from Switch C.
  13. # Configure a higher MED value for the route 1.0.0.0/8 advertised from Switch A to peer 192.1.1.2.
  14. # Define a prefix-list to permit route 1.0.0.0/8. 
    switch(config)# ip prefix-list pl_1 permit 1.0.0.0/24
  15. # 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. 
    switch(config)# route-map apply_med_50 permit
switch(route-map-apply_med_50)# match ip address prefix-list pl_1
switch(route policy)# set metric 50
switch(route policy)route-map apply_med_50 permit seq 20
switch(route policy)# exit

switch(config)# route-map apply_med_100 permit
switch(route policy)# match ip address prefix-list pl_1
switch(route policy)# set metric 100
switch(route policy)# route-map apply_med_100 permit seq 20
switch(route policy)# exit
  16. # 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.) 
    switch(config)# bgp 100
switch(bgp)# neighbor 193.1.1.2 route-map apply_med_50 out
switch(bgp)# neighbor 192.1.1.2 route-policy apply_med_100 out
switch(bgp)# exit
  17. # Display the BGP routing table on Switch D. 
    switch(config)# show ip bgp

Local AS : 100
Local Router-id : 194.1.1.1

BGP Table Version  : 1

Status codes: * - valid, > - best, i - internal, e - external, s - stale
Origin codes: i - IGP, e - EGP, ? - incomplete

Network        Nexthop    Metric LocalPref Weight AsPath
-------------------------------------------------------
*>e 1.0.0.0/24 194.1.1.2      50            0     100i

*>e 1.0.0.0/24 195.1.1.2     100            0     100i
  18. You can ensure that route 1.0.0.0/8 is the optimal route. 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.
  19. # Define an ip prefix-list on Router C, permitting route 1.0.0.0/8. 
    switch(config)# ip prefix-list pl_1 permit 1.0.0.0/8
  20. # 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.) 
    switch(config)# route-map localpref permit seq 10
switch(route-policy)# match ip address prefix-list pl_1
switch(route-policy)# set local-preference 200
switch(route-policy)# route-map localpref permit seq 20
  21. # Apply routing policy localpref to routes from peer 193.1.1.1. 
    switch(config)# router bgp 200
switch(bgp)# neighbor 193.1.1.1 route-map localpref in
switch(bgp)# exit
  22. # Display the routing table on Switch D. 
    switch(config)# show ip bgp

Local AS : 100
Local Router-id : 194.1.1.1

BGP Table Version  : 1

Status codes: * - valid, > - best, i - internal, e - external, s - stale
Origin codes: i - IGP, e - EGP, ? - incomplete

Network       Nexthop   Metric LocalPref Weight AsPath
-------------------------------------------------------
*>e 1.0.0.0/24 200.1.3.1    200            0     100i
* i 1.0.0.0/24              100            0     100i
  23. You can see that route 1.0.0.0/8 from Switch D to Switch C is the optimal route.