Atomic routing theory making an as route like a single node
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Atomic Routing Theory: Making an AS Route Like a Single Node. Rui Zhang-Shen [email protected] FIND Routing Workshop August 8, 2008. joint work with Jennifer Rexford and Yi Wang. Autonomous systems. The Internet (25k ASes). An autonomous system. What defines an AS?

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Atomic Routing Theory: Making an AS Route Like a Single Node

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Atomic routing theory making an as route like a single node

Atomic Routing Theory:Making an AS Route Like a Single Node

Rui Zhang-Shen

[email protected]

FIND Routing Workshop

August 8, 2008

joint work with Jennifer Rexford and Yi Wang


Autonomous systems

Autonomous systems

The Internet (25k ASes)

An autonomous system

What defines an AS?

How should the routers in an AS act?

R. Zhang-Shen


Policy based routing

Policy-based routing

  • Each AS has a well-defined policy, reflecting its

    • Goals, e.g., traffic engineering, security

    • Obligations, e.g., business contracts

  • Today’s practice

    • Specify the AS-level policies in terms of BGP attributes

    • Configure how each router selects and exports routes

  • Problem: Sometimes policies are violated

    • Even if routers are configured correctly

    • Due to peculiarities of protocol and implementation

    • Violations hard to detect, diagnose, or fix

R. Zhang-Shen


Example

Example

  • No transit between peers

  • Equally prefer customer and peer routes

  • Export full customer routes to peers

Peer 2

Peer 1

r1

A

C

B

r2

d

Customer 1

R. Zhang-Shen


Example1

Example

  • No transit between peers

  • Equally prefer customer and peer routes

  • Export full customer routes to peers

I can’t reach d any more!

r1

Peer 2

Peer 1

r1

X

A

C

B

r2

d

Customer 2

Customer 1

R. Zhang-Shen


Example2

Example

  • No transit between peers

  • Equally prefer customer and peer routes

  • Export full customer routes to peers

r1

I lost half of my users!

Peer 2

Peer 1

r1

X

d

A

C

B

r2

d

Customer 2

Customer 1

R. Zhang-Shen


Our approach

Our approach

  • Atomic Routing Theory

    • Mathematical model for policy

    • Precise definition of atomicity (realizing a policy)

    • Theoretical framework for exploring tradeoffs

      • Flexibility, correctness, and cost

    • Deriving minimum requirements for atomicity

  • Atomic BGP

    • Achieves both flexibility and correctness efficiently

    • Requires only minor changes to the router

      • Modify the decision process slightly

      • Change iBGP route dissemination slightly

R. Zhang-Shen


R oute a ssignment p roblem

Route Assignment Problem

rn

n

r3

R={

r1

rn

r2

}

1

2

Route Assignment

Constrained by the policy

3

e3=rn

en

e3

e1

from R

e2

E

R. Zhang-Shen


Policy and atomicity

Policy and atomicity

  • Policy P gives a set of route assignments

    • The AS is atomic if E2P(R)

  • If P can be decomposed into a policy for each neighbor, Pi

    • The AS can assign routes for each neighbor independently: Ei2Pi(R)

  • Decompose Pi (separate the easy and hard parts)

    • Route preference Bi() (defines a partial order)

    • Combinatorial preference Ci()(what’s left)

    • Realizing a policy means Ei2Ci(Bi(R)) (Bi() prunes routes)

    • Foreshadow distributed routing

R. Zhang-Shen


Distributed atomic routing

Distributed atomic routing

  • Disseminate all routes within the AS: realize any policy

  • If Ci() is inactive

    • Disseminate dominant routes according to Bi()

Atomic BGP

X

Policy

Flexibility

Today’s

practice

X

Atomic Routing

Dissemination

Overhead

BGP

X

R. Zhang-Shen


Art identifies bgp restrictions

ART identifies BGP restrictions

n

r3

R={

r1

rn

r2

}

1

Dissemination:

decouple from selection

B

Atomic BGP

2

Route Assignment

Constrained by the policy

A

3

Selection:

decouple links

e3=rn

en

e3

e1

from R

e2

BGP would force e2=rnor empty

No router can learn r1

R. Zhang-Shen


Atomic bgp offers

Atomic BGP offers

  • Correct policy and simple configuration

    • Define the AS-wide policies

    • Configure each router with it

    • No restrictions on the physical topology

  • Minimum protocol overhead

    • Dissemination of routes within the AS

    • Storage for routing tables

  • Incremental deployability

    • Only modest changes to the routers

    • Changes and benefits local to a single AS

    • Incrementally deployable within an AS

R. Zhang-Shen


Atomic routing theory can

Atomic Routing Theory Can…

  • When realizing an existing policy

    • Find out potential policy violations

    • Derive necessary protocol changes

  • When introducing new features to BGP

    • Ensure no new violations are introduced

  • When proposing new policy-based routing protocols

    • Ensure the desired policies can be realized

  • When analyzing multiple AS interactions

    • Correctly model an AS as a single node

R. Zhang-Shen


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