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:

MPLS solves 3 fundamental problems, individually or in concert

Multi-tenancy/VPNs

Traffic engineering

Fast reroute

4 bytes in a shim header, technically not a label, but we call it that

20 bits for label value, 2^20 ~= 1 million values (this is important)

3 bits for EXP, QoS really

1 S-bit to signal bottom of stack

8 bits TTL

Label depth is theoretically infinite, but some HW platforms have a tolerance

Many ways to allocate labels

LDP transport

LDP pseudowire

BGP labeled unicast

BGP based IP VPNs (VPNv4/v6)

BGP pseudowire

SR (really built into OSPF and ISIS for distribution)

RSVP-TE

Some forward rules are worth mentioning (basic LDP/BGP-LU environment)

If route learned via IGP/static, LDP label must be used

If route learned via BGP, BGP label must be used

No exceptions

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

Is MPLS is a tunnel or not:

Nick says always

Russ says sometimes, depending on label depth

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?”

 

Outro Music:

Danger Storm Kevin MacLeod (incompetech.com)

Licensed under Creative Commons: By Attribution 3.0 License

http://creativecommons.org/licenses/by/3.0/