Episode 25 – MPLS Part 1

In a new protocol deep-dive series, Nick Russo and Russ White return to discuss MPLS. In part one, we discuss the primary use cases for MPLS, label allocation, and what SD-WAN means for the future of MPLS.


Show Notes:

  1. MPLS solves 3 fundamental problems, individually or in concert
    1. Multi-tenancy/VPNs
    2. Traffic engineering
    3. Fast reroute
  2. 4 bytes in a shim header, technically not a label, but we call it that
    1. 20 bits for label value, 2^20 ~= 1 million values (this is important)
    2. 3 bits for EXP, QoS really
    3. 1 S-bit to signal bottom of stack
    4. 8 bits TTL
  3. Label depth is theoretically infinite, but some HW platforms have a tolerance
  4. Many ways to allocate labels
    1. LDP transport
    2. LDP pseudowire
    3. BGP labeled unicast
    4. BGP based IP VPNs (VPNv4/v6)
    5. BGP pseudowire
    6. SR (really built into OSPF and ISIS for distribution)
    7. RSVP-TE
  5. Some forward rules are worth mentioning (basic LDP/BGP-LU environment)
    1. If route learned via IGP/static, LDP label must be used
    2. If route learned via BGP, BGP label must be used
    3. No exceptions
  6. Penultimate Hop Popping: second to last hop removes topmost label when signaled with imp-null from last hop along a given LSP, saves a lookup
  7. Is MPLS is a tunnel or not:
    1. Nick says always
    2. Russ says sometimes, depending on label depth
  8. Dispel rumor: MPLS is a technology, not a service. It’s incorrect to ask “Will SD-WAN supplant MPLS?” This is akin to saying “Will pizza delivery service supplant water?” A more reasonable question would be “Will SD-WAN supplant private WANs?”

 


Russ White
Guest
Nicholas Russo
Guest

Jordan Martin
Co-Host
Eyvonne Sharp
Co-Host


Outro Music:
Danger Storm Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0 License
http://creativecommons.org/licenses/by/3.0/

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