# AS path extensions

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**Curtis Villamizar**

*Wed Mar 8 20:37:25 CET 1995*

In message <199503052215.AA16699 at cat.isi.edu>, Cengiz Alaettinoglu writes: >>Hi,>>Here is the latest document on this extension. Comments are>welcome. Thanks.>>I do not remember if I have already sent this. I am sorry if I did so.>>CengizCengiz, Thanks for the doc. I think the Cisco syntax is also known as the Yakov memorial AS path syntax. It is documented in the gated config section as well. See: http://www.gated.cornell.edu http://www.gated.cornell.edu//gated-R3_5Alpha_9/config_guide/aspath.html If Cisco is using a different syntax, then don't use it. Use the syntax in RFC 1164 (same as gated syntax). The gated config section describes this concisely. You can just cite the RFC or duplicate it. Curtis The gated syntax is below: [ ... ] AS path regular expressions Technically, an AS path regular expression is a regular expression with the alphabet being the set of AS numbers. An AS path regular expression is composed of one or more AS paths expressions. An AS path expressions is composed of AS path terms and AS path operators. AS path terms An AS path term is one of the following three objects: autonomous_system . ( aspath_regexp ) autonomous_system Is any valid autonomous system number, from one through 65534 inclusive. . matches any autonomous system number. ( aspath_regexp ) parentheses group subexpressions--an operator, such as * or ? works on a single element or on a regular expression enclosed in parentheses AS path operators An AS path operator is one of the following: aspath_term {m,n} aspath_term {m} aspath_term {m,} aspath_term * aspath_term + aspath_term ? aspath_term | aspath_term aspath_term {m,n} a regular expression followed by {m,n} (where m and n are both non-negative integers and m <= n) means at least m and at most n repetitions. aspath_term {m} a regular expression followed by {m} (where m is a positive integer) means exactly m repetitions. aspath_term {m,} a regular expression followed by {m,} (where m is a positive integer) means m or more repetitions. aspath_term * an AS path term followed by * means zero or more repetitions. This is shorthand for {0,}. aspath_term + a regular expression followed by + means one or more repetitions. This is shorthand for {1,}. aspath_term ? a regular expression followed by ? means zero or one repetition. This is shorthand for {0,1}. aspath_term | aspath_term matches the AS term on the left, or the AS term on the right. Last updated 1994/03/16 21:38:07. gated at gated.cornell.edu -------- Logged at Thu Mar 9 05:22:19 MET 1995 ---------

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