MPLS In Perspective Kireeti Kompella Distinguished Engineer Juniper

MPLS In Perspective Kireeti Kompella Distinguished Engineer Juniper Networks 1

Menu IP salad with horseradish dressing ATM flambee MPLS stewed in its own juice For afters Services double espresso Revenue a la mode Copyright Juniper Networks, 2001 2

IP – Good Enough ™ Well-architected, worked out in detail – NOT! Realization: can’t predict the future Make it reasonable Make it flexible Make it extensible stuff above transport network stuff below Copyright Juniper Networks, 2001 3

So Easy to Forget IP started out with e-mail … … and data services ftp news Now: the “Web”, voice, video, … Also, SLAs, grades of service, … Copyright Juniper Networks, 2001 4

IP Control Plane Again, just good enough But again, flexible, extensible DV routing was fine for quite a while Just in time, along came link state Now: is convergence “in a few seconds” good enough? Copyright Juniper Networks, 2001 5

Good Enough™ Can Get Better Fast to ultrafast convergence “Bullet-proof” IP Hitless restart? “Business” IP Make me money – new services, Go. S Don’t lose me money – uptime, SLAs Copyright Juniper Networks, 2001 6

AA Connection-oriented Does everything and does it well Anticipated all future uses and factored them in Philosophical mismatch with IP L 1 AA L AA 2 L 3 AA /4 L 5 ATM – Perfectionist’s Dream stuff above transport network Copyright Juniper Networks, 2001 ATM 7

MPLS If (ATM = Frame Relay on steroids) then (MPLS = ATM on happy juice) Make it just Good Enough ™ Despite all efforts to make it perfect IP control plane IP philosophy Copyright Juniper Networks, 2001 8

What Does MPLS Offer? Tunnels Drop a packet in, and out it comes at the other end without being IP routed Explicit (source) routing (circuits) Label stack 2 -label stack: “outer” label defines the tunnel; “inner” label demultiplexes Layer 2 independence Copyright Juniper Networks, 2001 9

Why Tunnels? Can’t IP route Non-IP packets with private addresses Don’t want to IP route “BGP-free” core Multicast Copyright Juniper Networks, 2001 10

How Tunnels? MPLS: LDP – “automagic” tunnels that follow IP routing IP: IP-in-IP, GRE, IPSec, UTI Can one tunnel do multiple things? Tunnel demux Copyright Juniper Networks, 2001 11

Tunnel Comparison MPLS (LDP) tunnels Small header Label stacking Signaling for demux Automagic tunnels Tracks IP routing Harder to spoof No data security IP tunnels Big header No stacking (*) No signaling (yet) Configured tunnels Duh! Spoofable IPSec Copyright Juniper Networks, 2001 12

Bottom Line on Tunnels Don’t need MPLS for tunnels But MPLS tunnels have some nice properties Decision (should be) based on cost of deploying new protocol vs. benefits Copyright Juniper Networks, 2001 13

Why Explicit Routing? Traffic Engineering Fast reroute Guaranteed bandwidth Probably others Connection-oriented paradigm nicely complements IP’s connectionlessness Copyright Juniper Networks, 2001 14

Traffic Engineering Is ATM the best way to engineer traffic? Or is it MPLS? Or can we do just fine with IP? First question: do you need traffic engineering? What part of network? Copyright Juniper Networks, 2001 15

Traffic Engineering Steps First, determine how to lay out traffic on the physical topology Measure traffic (e. g. , city-pair-wise) Crunch numbers Second, do something to convince the packets to follow your plan Copyright Juniper Networks, 2001 16

Traffic Engineering Options BGP – play with communities, filtering IGP – play with metrics Linear programming can help Source routing ATM MPLS Copyright Juniper Networks, 2001 17

Traffic Engineering Warning: read at your own risk! Fine-grained Traffic Engineering needs some form of source routing Specific incremental changes much easier with source routing Change a single city-pair flow Reacting to a link failure Copyright Juniper Networks, 2001 18

Linear Programming TE among N cities: N² city pairs Set up N² by N² matrix for LP Matrix multiplication/inversion is O(M³) for M x M matrix; simplex is O(M³) matrix operations So, LP problem is O(N 12) Also can’t deal with “looped routes” Copyright Juniper Networks, 2001 19

Fast Reroute Can MPLS re-route as fast as SONET (50 ms)? Can IP re-route as fast as MPLS? Do packets get dizzy if they are rerouted too fast? Copyright Juniper Networks, 2001 20

Fast Reroute (2) First question: how fast is fast? Do you really need 50 ms failover? Second question: can you reroute really quickly while maintaining network stability? Third question: what are the scalability issues with fast reroute? Copyright Juniper Networks, 2001 21

Fast Reroute Comparison IP All nodes must be told of failure Fast propagation, fast SPF trigger: how stable? One step to full reconvergence MPLS (RSVP-TE) Only the two ends of the link need be told (no signaling) Local operation: explicit routing; more stable Two step process: detour + converge Copyright Juniper Networks, 2001 22

Fast Reroute: MPLS vs. IP C 10 pkt to B 1000 A 10 B IP routing to B MPLS detour to B Copyright Juniper Networks, 2001 23

Guaranteed Bandwidth Again, first question: do you need it? If so, you need source routing, CAC and some way of signaling b/w RSVP-TE can do this ATM could probably do it better Copyright Juniper Networks, 2001 24

“MPLS” Services IP VPNs (RFC 2547 et al) Layer 2 transport Layer 2 VPNs Transparent LAN Service TDM over MPLS over TDM over … Electricity over photons? Have we gotten a little carried away? Copyright Juniper Networks, 2001 25

“MPLS” Services (2) Most of these services need tunnels Not really MPLS services MPLS-geeks definitely responsible Some of these services enhanced by source routing More services may mean more revenue, could also keep you awake at night Copyright Juniper Networks, 2001 26

Revenue RFC 2547 New service – recent deployment Give it a shot, or run like hell? Or wait? Layer 2 VPNs Old service – lots of deployment New transport – is it Good Enough? Guaranteed bandwidth, Diff Serv, …? Copyright Juniper Networks, 2001 27

Things to Ponder Can Good Enough™ IP stay ahead of the curve? Even if so, can MPLS help? Is MPLS a support, a crutch or a banana peel? Is connection-orientedness a useful addition to connectionless IP? What services, when, how far to go? Copyright Juniper Networks, 2001 28

My Biases Vendor MPLS geek Protocols freak Neutral about ATM IP rules! Reasonably agnostic Copyright Juniper Networks, 2001 29

Thank you! http: //www. juniper. net kireeti@juniper. net 30