I have to admit I LOVE MPLS.  I admit, I didn’t love it so much when I was first learning.  I found it kinda hard at first.  But then I absolutely loved it once I “saw” it.

Newer to MPLS and Want To Play?

I had a friend, Bryan Brzezinski, that was very new to MPLS. So I created all of this for him.  Like a one-on-one custom built class.   The YouTubes, the sniffer traces, the PDF of all the diagrams, the 2nd blog and YouTube. Figured I’d pass it along to share with everyone else.  The class is in two sections

1. MPLS L3VPN: Label Following Fun with Fish (this blog) to set the foundation.

2. The “Case of the Broken MPLS L3VPN” (next blog) to play network detective and put into action what we have learned here.

This blog will give a big picture overview of what is in the YouTube.  Plus a timeline step by step you can use to jump forward to varying parts in the YouTube.  It will also have files you can download for reference that you can use to ride-a-long with both YouTubes.

The Playground

Our environment for beginner MPLS follow the label fun will be the MPLS L3VPN environment above.  For this YouTube and blog we are ONLY following the labels – the propagation of them with BGP and LDP as well as the following of those labels thru the core in the middle.

We will not get into RDs, RTs, or VRFs in any detail for this blog/youtube video.  We are just trying to see the big picture right now.

The only thing we will do in reference to that is point out that the interface on Charlie6 towards R1 is in a VRF and that Charlie17’s interface towards R2 is also in a VRF.

I have always learned best when I look at a sniffer trace.  So what I did was put a sniffer between Charlie6 and Charlie7 above while the interface on Charlie6 was shutdown.  Start the sniffer capture… and then no shut the interface.  So in the pcap file below you will find everything including 3 key things we will look into in more detail in the YouTube –

• BGP VPNv4 startup and updates between Charlie6 and Charlie17
• LDP startup and advertisements between Charlie6 and Charlie7
• The successful ping between R1’s loopback and R2’s loopback and what labels were used

FILES:

• All PowerPoint diagrams in PDF format: Fish_Label_Fun.pdf
• Sniffer Trace: Label_Following_Fun.pcap

I suggest downloading the PDF and the PCAP file and then clicking on the YouTube link.

YouTube Link

YouTube Link: https://www.youtube.com/watch?v=V4D8uqSCBKA

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Timeline Breakdown of Youtube (~25 minutes)

• Intro and Overview – (Start  til 4:33)
• MPLS L3VPN (4:34 – 8:04) — MultiProtocol label switching. Big picture. Pic of typical protocols use for advertising labels in a MPLS L3VPN environment – BGP for the inner (vpn) label and LDP for the outer label.
• Placement of the Sniffer (8:05 – 9:30)
• BGP Labels (9:31 -11:25) — line 81 in the sniffer trace will show 10.100.100.17 (Charlie17) sends an update to Charlie6 that Charlie17 (10.100.100.17) can get to 10.100.100.2 and to use a label (tag) of 20.

side note — I learned MPLS when Cisco still had TDP (tag distribution protocol) actively in environments.  So I sometimes use the word tag instead of label.

• Are We Ready? (11:26 – 13:30)   Question: If a Ping comes into Charlie6 from R1 to get to 10.100.100.2 – can Charlie6 just push label 20 on it and send it to Charlie7?
• LDP Labels (13:31 – 15:28) — looking at the sniffer trace we can see Charlie7 (10.100.100.7) advertising to Charlie6, via their LDP neighbor relationship, that Charlie7 (10.100.100.7) can help Charlie6 get to 10.100.100.17.  And to use a label of 23.
• Putting It All Together – Time to Follow the Labels. 🙂
  
  • Charlie6 Perspective (15:29-17:53)
  • Over to Charlie7 (17:54 – 19:16)
  • A Caveat about Charlie16 (19:17 – 20:25)
  • Charlie16‘s View (20:26 – 21:44)
  • Back to Charlie17 (21:45 – 22:57)
  • Wireshark Fun (22:58 to 24:56)- Checking out the sniffer trace to see the MPLS Labels used between Charlie6 and Charlie7 and tweaking wireshark columns

Ready for Part 2?  — The “Case of the Broken MPLS L3VPN”