Thursday, August 11, 2011

Configuring BGP - Dual Multihomed Design

We've already laid out the ground work in my previous blogtorial "Configuring BGP - Dual Homed Design". So all we are going to have to do is bring up 2 more bgp peers. 1 on R1 and 1 on R2 to connect ISP-B with the ASN 33333.


Here is the topology so let's get going.

Relevant configurations are posted below.


On R1 let's get interfaces, NAT and BGP configured to work with R6.

R1#sh run int gig3/0
interface GigabitEthernet3/0
 description Connected to R6
 ip address 13.13.13.1 255.255.255.0
 ip nat outside
 negotiation auto
end

R1#show run | sec route-map

route-map eBGPNAT-ISPB permit 10
 match ip address 1
 match interface GigabitEthernet3/0

R1#sh run | incl ip nat
ip nat inside source route-map eBGPNAT-ISPB interface GigabitEthernet3/0 overload

R1#sh run | sec bgp
router bgp 22222
 no synchronization
 bgp log-neighbor-changes
 bgp redistribute-internal
 network 11.11.11.0 mask 255.255.255.0
 network 22.22.22.0 mask 255.255.255.0
 neighbor 11.11.11.4 remote-as 11111
 neighbor 11.11.11.4 route-map SETEBGPLOCALPREF in
 neighbor 13.13.13.6 remote-as 33333
 neighbor 13.13.13.6 route-map SETEBGPLOCALPREF in
 neighbor 22.22.22.2 remote-as 22222
 neighbor 22.22.22.2 next-hop-self
 neighbor 22.22.22.2 route-map SETIBGPDEFLOCALPREF in
 no auto-summary

Now let's get R2 configured.

R2#sh run int gig3/0
interface GigabitEthernet3/0
 description Connected to R7
 ip address 14.14.14.2 255.255.255.0
 ip nat outside
 ip virtual-reassembly
 negotiation auto
end

R2#show run | sec route-map
route-map eBGPNAT-ISPB permit 10
 match ip address 1
 match interface GigabitEthernet3/0

R2#sh run | incl ip nat
ip nat inside source route-map eBGPNAT-ISPB interface GigabitEthernet3/0 overload

R2#sh run | sec bgp
router bgp 22222
 no synchronization
 bgp log-neighbor-changes
 bgp redistribute-internal
 network 12.12.12.0 mask 255.255.255.0
 network 22.22.22.0 mask 255.255.255.0
 neighbor 12.12.12.5 remote-as 11111
 neighbor 12.12.12.5 route-map SETEBGPLOCALPREF in
 neighbor 14.14.14.7 remote-as 33333
 neighbor 14.14.14.7 route-map SETEBGPLOCALPREF in
 neighbor 22.22.22.1 remote-as 22222
 neighbor 22.22.22.1 next-hop-self
 neighbor 22.22.22.1 route-map SETIBGPDEFLOCALPREF in
 no auto-summary

R6 and R7 are setup exactly as R4 and R5 from the previous blogtorial "Configuring BGP - Dual Homed Design" with the exception of the ASN and ip addresses. 

Few show commands to verify connectivity, default routes and local preference. 



1st Failover scenario: R1 looses connectivity to ISP-A. 


Soon as I shut the interface for ISP-A, the default route from ISP-B takes over and now I am using ISP-B for R1's internet. R2 at this time is still using ISP-A since R2's connection to ISP-A works. 

Full router configurations for all 7 routers. 


Many more articles to come so stay tuned!! Please subscribe to my posts by clicking "Join this Site" on the right.