rtconfig & aspath filter

Ruediger Volk, Deutsche Telekom NP - FMED51.. rv at NIC.DTAG.DE
Mon Aug 29 15:36:28 UTC 2011

Hi Are,

  > Hi,
  > I'm trying to get rtconfig to generate as path filters, but it wants to 
  > expand the AS into prefix lists.
  > Is there any obvious ways to do this?
  > I've tried both to use filter set and as set.
  > example:
  > import:     from AS65009  action pref = 660; 
  > community.append(65009:19999); accept AS65008:AS-65009-PREFER
well, in RPSL syntax this means
	accept prefixes matching the route-set you get by resolving

The concept that is offered by RPSL is filtering by AS path regular expressions;
and you can reference AS-sets within those regexps.
RPSL syntax requires the reg exps to be enclosed in <>;
note that the regexpsare NOT anchored.
So	<AS65008:AS-65009-PREFER> matches all paths in which an AS from
				     ... occurs (anywhere);
	<^AS65008:AS-65009-PREFER> - ... is next hop AS
	<AS65008:AS-65009-PREFER$> - ... is origin AS

  > as-set:     AS65008:AS-65009-PREFER
  > descr:      preferred AS
  > members:    AS1, AS2
  > OR
  > import:     from AS65009  action pref = 660; 
  > community.append(65009:19999); accept FLTR-AS-65009-PREFER
  > filter-set: FLTR-AS-65009-PREFER
  > descr:      preferred AS
  > filter:     AS1 OR AS2
same syntax and semantics apply here!

  > R,
  > -Are
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Ruediger Volk

Deutsche Telekom AG -- Internet Backbone Engineering

E-Mail:  rv at NIC.DTAG.DE

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