I would like to dedicate this post to MPLS L3 VPNs troubleshooting and more particularly using the Traceroute command. It can be sometimes difficult to find out where is the issue when testing connectivity between sites attaches to a MPLS VPN backbone. I will explain the behavior of Traceroute in MPLS VPN environment which is quite different than in “classical” IP environment. Finally I will talk about the MPLS LSP Ping feature and how to use it to detect break in MPLS LSP.
I am using almost the same topology as the one used in this post: Basic MPLS. I have just added a P router.
Cisco 2691/12.4(15)T11 Adv IP services
The following is already configured:
- MP-iBGP between R2 and R5
- EBGP between R2 and R1, R5 and R6
- OSPF area 0 between R2,R3,R4,R5
- LDP between R2,R3,R4,R5
- R3 and R4 are P routers and R2 and R5 are PE routers
- R1 is representing the CE device at Site A announcing its loopback address 220.127.116.11/32
- R2 is representing the CE device at Site B announcing its loopback address 18.104.22.168/32
In this troubleshooting scenario we want to focus on the loopbacks reachability between Site A and Site B.
I would like to share a basic MPLS configuration example where I will explain how MPLS works and what are the different steps in order to configure it. This example is not related to MPLS layer 3 VPNs, this is just going to be the basic underlying logic of how an MPLS tunnel on its own works so I will neither talk about VRF nor MP-BGP which is the VPNv4 address family in order to exchange the customer routes and the MPLS VPN labels.
Let´s consider the following topology:
PE routers R2 and R4
P router: R3
CE routers R1 and R5
It has been a while since I haven´t written in the blog but I have been busy with work and training.
I have now completed my BGP and MPLS exam which will give me a solid understanding for my CCIE training.
In order to pass these 2 exams I have used the student and lab guides from Cisco. I have done all the labs using real device as well as GNS3 (especially for MPLS where I used 13 routers!)
I attach the network diagram I used for MPLS training.