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USC / Information Sciences Institute Cengiz Alaettinoglu, IETF July ?95

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Logical Combination

as-in: from AS2 1 accept

AS-ANSLA AND NOT AS1322 OR {128.8.0.0/16}

USC / Information Sciences Institute Cengiz Alaettinoglu, IETF July ?95

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Multiple Interconnections

aut-num: AS1 as-in: from AS2 1 accept {128.8.0.0/16} interas-in: from AS2 l1 r1 (pref=1) accept {128.8.0.0/16} interas-in: from AS2 l2 r2 (pref=2) accept {128.8.0.0/16} interas-out: to AS2 ...

AS2AS1 128.8/16 l1 r1

l2 r2

USC / Information Sciences Institute Cengiz Alaettinoglu, IETF July ?95

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AS Path Expressions in Policy

Many providers have AS path based policies:

as-in: ... accept AS1 is not in the AS path

as-out: ... announce AS1 is the first AS in the AS path

Need AS Path Expressions!

USC / Information Sciences Institute Cengiz Alaettinoglu, IETF July ?95

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AS Path Regular Expressions

ASn ?ASn? . any AS number [AS1 AS2 AS4-AS6] AS1, AS2, AS4, AS5, AS6 [^AS1 AS2 AS4-AS6] AS3, AS7, AS8, ... ^ beginning of an AS path $ end of an AS path exp* exp+ exp? 0 or more, 1 or more, 0 or 1 exp1 exp2 catenation exp1 | exp2 alternative ()

USC / Information Sciences Institute Cengiz Alaettinoglu, IETF July ?95

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AS Path Expression

< AS-Path-Regular-Expression >

matches routes whose AS paths are matched

by the AS-Path-Regular-Expression

USC / Information Sciences Institute Cengiz Alaettinoglu, IETF July ?95

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AS Path Expressions in Policy

aut-num: AS1

as-in: from AS2 1 accept NOT <AS1>

as-in: from AS2 1 accept <^AS1$>

as-out: to AS2 announce <^[AS1 AS3 AS4 AS5]>

Existing tools will break!