AS path extensions

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.
> 
> Cengiz


Cengiz,

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  ---------