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/