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?”  

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