BGP Multihoming

[NetworkGuy!]

Hi

I have the present scenario and would like to ask for any suggestions / best practises

There is two buildings and 1 ISP Circuit/ routers in each building. I would like to do BGP multihoming - I want building A to be primary and building B to be secondary. both buildings are connected to each other by internal fibres

I want all traffic to go through Building 1 (if things are well) but if the fibre breaks, and if router in Building 1 goes down, then all traffic through Building 2. 

But if the fibre breaks, then I want all local traffic to go through local routers - is this possible? ISP prepared to do bgp config as my design

1/ would cross peering between the circuits help? (like R1 has BGP peer to ISP Circuit 1 and 2 and R2 has BGP peer to ISP circuit 1 and 2)? 

2. or can i design as Active/Active - how will incoming traffic behave? no issue with public address - I have many public ip address available

3. any other design recommendations even if its something which is out of the box! ?

[Julio E. Moisa]

Hi

You could create an iBGP peering between R1 (primary site) and R2 (secondary site) using the directly connected IPs or using loopbacks (in this case you require a IGP as well).

Once you have the iBGP peering, you can use BGP attributes to move the traffic and prefer a path over other. The basic configuration could be something like:

R1 (Primary site)

int g0/0

description TO-ISP1

ip address 190.x.x.2 x.x.x.x

no shut

int g0/1

description TO-R2-SITE2

ip address 10.0.0.1 255.255.255.252

no shutdown

route-map INBOUND permit 5

set local-preference 10000

route-map OUTBOUND permit 5

set as-path prepend 100 100 

router bgp 100

no sync

no auto

neighbor 190.x.x.1 remote 6500

neighbor 190.x.x.1 route-map INBOUND in

neighbor 190.x.x.1 route-map OUTBOUND out

neighbor 10.0.0.2 remote 100

neighbor 10.0.0.2 next-hop-self

R2 (Secondary site)

int g0/0

description TO-ISP2

ip address 200.x.x.2 x.x.x.x

no shut

int g0/1

description TO-R2-SITE2

ip address 10.0.0.2 255.255.255.252

no shutdown

route-map INBOUND permit 5

set local-preference 5000

route-map OUTBOUND permit 5

set as-path prepend 100 100 100 100

router bgp 100

no sync

no auto

neighbor 200.x.x.1 remote 6600

neighbor 200.x.x.1 route-map INBOUND in

neighbor 200.x.x.1 route-map OUTBOUND out

neighbor 10.0.0.1 remote 100

neighbor 10.0.0.1 next-hop-self

Also take in consideration you must avoid that your network becomes a transit network using: ip as-path access-list 1 permit ^$ going out direction. You can filter the traffic using Prefix List in order to avoid extra CPU utilization and by security reasons. You can also apply load balance if it is required. 

Hope it is useful

:-)