Transcript MPLS In Perspective

MPLS In Perspective
Kireeti Kompella
Distinguished Engineer
Juniper Networks
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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
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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
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2001
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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, …
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2001
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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?
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2001
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Good Enough™ Can Get Better
Fast to ultrafast convergence
“Bullet-proof” IP
Hitless restart?
“Business” IP
Make me money – new services, GoS
Don’t lose me money – uptime, SLAs
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2001
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ATM – Perfectionist’s Dream
Connection-oriented
Does everything and
does it well
Anticipated all
future uses and
factored them in
Philosophical
mismatch with IP
stuff above
transport
network
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2001
ATM
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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
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2001
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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
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2001
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Why Tunnels?
Can’t IP route
Non-IP packets
IP packets with private addresses
Don’t want to IP route
“BGP-free” core
Multicast 
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2001
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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
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2001
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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
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2001
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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
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2001
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Why Explicit Routing?
Traffic Engineering
Fast reroute
Guaranteed bandwidth
Probably others
Connection-oriented paradigm nicely
complements IP’s connectionlessness
Copyright Juniper Networks,
2001
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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
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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
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Traffic Engineering Options
BGP – play with communities, filtering
IGP – play with metrics
Linear programming can help
Source routing
ATM
MPLS
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2001
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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
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2001
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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(N12)
Also can’t deal with “looped routes”
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2001
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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 rerouted too fast?
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2001
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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?
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2001
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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
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2001
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Fast Reroute: MPLS vs. IP
C
10
pkt to B
1000
A
10
B
IP routing to B
MPLS detour to B
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2001
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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
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“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?
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2001
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“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
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2001
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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, …?
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2001
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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?
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2001
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My Biases
Vendor
MPLS geek
Protocols freak
Neutral about ATM
IP rules!
Reasonably agnostic
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2001
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Thank you!
http://www.juniper.net
[email protected]
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