ecmp or multipath in bgp - ebg and ibgp

[mailvishnu03]

Hi,

Just want to know how to form ecmp in the below topology.

--- R1 --- AS100 --- R2 --- AS 200 --- R3 --- AS100 --- R4 ---

Here in my topology EBGP between R1 -- R2 and R3 --- R4. IBGP between R2 --- R3. I am trying to redistribute same route from R1 and R4. Is it possible to get it as multipath in R2 or R3.

[Vasilii Mikhailovskii]

Hello.

As I understood, traffic is originated in AS 200 and reaches R2/R3 device. And you want to load-balance over R1 and R4.

If so - you have some options.

Option 1 (if R2/R3 are directly connected):

• make sure traffic always hits R2;
• configure R2 for eibgp multipath;
• make sure R3 prefers eBGP.

Option 2 (if R2/R3 are not directly connected):

• some L3 device is a first hop for the traffic;
• the device does multipath/load-balancing over R2 and R3;
• R2 and R3 always prefer eBGP.

[mailvishnu03]

 

Attaching the topology : In the attached topology from R1 and R4 we are getting a route 10.1.1.1.

In R2 need to display it as ECMP/multipath. In R2's routing table i need to have a route for 10.1.1.1 as ecmp (i.e) 10.1.1.1 can be reachable via R1 and R3.