1 mpls in perspective kireeti kompella distinguished engineer juniper networks
TRANSCRIPT
Copyright Juniper Networks,
2001 2
Menu
IP salad with horseradish dressingATM flambeeMPLS stewed in its own juice
For aftersServices double espressoRevenue a la mode
Copyright Juniper Networks,
2001 3
IP – Good Enough ™
Well-architected, worked out in detail – NOT!Realization: can’t predict the futureMake it reasonableMake it flexibleMake it extensible
stuff above
transport
network
stuff below
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2001 4
So Easy to Forget
IP started out with e-mail …… and data services
ftpnews
Now: the “Web”, voice, video, …Also, SLAs, grades of service, …
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2001 5
IP Control Plane
Again, just good enoughBut again, flexible, extensible
DV routing was fine for quite a whileJust in time, along came link stateNow: is convergence “in a few seconds” good enough?
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2001 6
Good Enough™ Can Get Better
Fast to ultrafast convergence“Bullet-proof” IP
Hitless restart?
“Business” IPMake me money – new services, GoSDon’t lose me money – uptime, SLAs
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2001 7
ATM – Perfectionist’s Dream
Connection-orientedDoes everything and does it wellAnticipated all future uses and factored them inPhilosophical mismatch with IP
stuff above
transport
network
ATM
AAL
1AA
L 2
AAL
3/4
AAL
5
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2001 8
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 planeIP philosophy
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2001 9
What Does MPLS Offer?
TunnelsDrop 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
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2001 10
Why Tunnels?
Can’t IP routeNon-IP packetsIP packets with private addresses
Don’t want to IP route“BGP-free” coreMulticast
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2001 11
How Tunnels?
MPLS: LDP – “automagic” tunnels that follow IP routingIP: IP-in-IP, GRE, IPSec, UTICan one tunnel do multiple things?
Tunnel demux
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2001 12
Tunnel Comparison
MPLS (LDP) tunnelsSmall headerLabel stackingSignaling for demuxAutomagic tunnelsTracks IP routingHarder to spoofNo data security
IP tunnelsBig headerNo stacking (*)No signaling (yet)Configured tunnelsDuh!SpoofableIPSec
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2001 13
Bottom Line on Tunnels
Don’t need MPLS for tunnelsBut MPLS tunnels have some nice propertiesDecision (should be) based on cost of deploying new protocol vs. benefits
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2001 14
Why Explicit Routing?
Traffic EngineeringFast rerouteGuaranteed bandwidthProbably othersConnection-oriented paradigm nicely complements IP’s connectionlessness
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2001 15
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?
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2001 16
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
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2001 17
Traffic Engineering Options
BGP – play with communities, filteringIGP – play with metrics
Linear programming can help
Source routingATMMPLS
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2001 18
Traffic Engineering
Warning: read at your own risk!Fine-grained Traffic Engineering needs some form of source routingSpecific incremental changes much easier with source routing
Change a single city-pair flowReacting to a link failure
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2001 19
Linear Programming
TE among N cities: N² city pairsSet up N² by N² matrix for LPMatrix multiplication/inversion is O(M³) for M x M matrix; simplex is O(M³) matrix operationsSo, LP problem is O(N12)Also can’t deal with “looped routes”
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2001 20
Fast Reroute
Can MPLS re-route as fast as SONET (50ms)?Can IP re-route as fast as MPLS?Do packets get dizzy if they are re-routed too fast?
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2001 21
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 22
Fast Reroute Comparison
IPAll 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 stableTwo step process: detour + converge
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2001 23
Fast Reroute: MPLS vs. IP
A B
C
100010
10
IP routing to B
pkt to B
MPLS detour to B
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2001 24
Guaranteed Bandwidth
Again, first question: do you need it?If so, you need source routing, CAC and some way of signaling b/wRSVP-TE can do thisATM could probably do it better
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2001 25
“MPLS” Services
IP VPNs (RFC 2547 et al)Layer 2 transportLayer 2 VPNsTransparent LAN ServiceTDM over MPLS over TDM over …Electricity over photons?Have we gotten a little carried away?
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2001 26
“MPLS” Services (2)
Most of these services need tunnelsNot really MPLS services
MPLS-geeks definitely responsibleSome of these services enhanced by source routingMore services may mean more revenue, could also keep you awake at night
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2001 27
Revenue
RFC 2547New service – recent deploymentGive it a shot, or run like hell? Or wait?
Layer 2 VPNsOld service – lots of deploymentNew transport – is it Good Enough?
Guaranteed bandwidth, Diff Serv, …?
Copyright Juniper Networks,
2001 28
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 29
My Biases
VendorMPLS geekProtocols freakNeutral about ATMIP rules!Reasonably agnostic