Transit AS with MPLS VPN

Senario : To enable communication between AS 50 and AS 20 without redistributing BGP routers into IGP (AS 134). We select OSPF as IGP which runs on R3,R1,R4.

Note: I have only shown configuration from one router if the configurations are identical. Final configuration and .net files can be downloaded from here

Initial config:

Configure IP address as per topology.

Configure OSPF (IGP) on R3 (Lo,ser01/), R1(ser 0/1,Fa1/0) and R4 (Lo,Fa0/0)

From R1:

Configure BGP (AS50) on R5 and advertise Lo

Configure BGP (AS20) on R2 and advertise Lo

Note:

R1 runs only OSPF (IGP).

EBGP :R4-R2

EBGP :R3-R5

We will be using MPLS VPN to tunnel AS 50 and AS 20 traffic via transit AS 134.

Step1: Enable basic mpls on AS 134 routers.

Make sure CEF is enabled. Enable label switching on interfaces.

Serial 0/1 and fas 1/0 on R1, Serial 0/1 o R3 and Fas 0/0 on R4

From R1:

Verify label switching is functioning, Output from R1

R1 established neighborship with R3 and R4 and FIB is populated.

Step2: Configure BGP

From R3

From R4

Verify:

Step 3: VPN.

Create VRF (AS50_AS20) on R3 and R4.

From R3

Configure address family and Establish IBGP inside VRF.

From R3

Enable PE interface into VRF routing.

From R3

Final testing:

We have completed the configuration part. Lets us verify R2 routing table.

The output shows R2 has received BGP routes from R5, but the ping fails. My trace (not included here) further shows the packet is dropping at R3. We already verified LDP in the beginning, hence look for something else.

Meantime i have noticed the following logs on R3 and R4 console.

It says the loopback to which IBGP is established should be configured as /32 in order for the VPN to work. Hence I reconfigured the subnet mask for loopback 0 on both R3 and R4 to /32. (As per my topology it was /24)

Lets test the reachability again

Now we have successfully transporting BGP NLRIs form AS 50 to AS 20 and vice versa which is transparent to IGP router R1.

R1’s routing table.