05-30-2008 07:56 AM - edited 03-03-2019 10:10 PM
guys if we use permit ^$ what does that mean ??? will it allow routes or not???? cheers
05-30-2008 08:19 AM
It will allow routes from within the same AS but not from any other AS so they could be received from an IGBP session but not an EBGP session.
Jon
05-30-2008 08:57 AM
HI, [Pls Rate all Informative POST]
In addition to Jon POST, refer link below for cisco Document on, Using Regular Expression in BGP.
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a92.shtml
Hope I am Informative.
Pls Rate all Informative POST
Best Regards,
Guru Prasad R
05-30-2008 09:35 AM
Hi:
That regexp (regular expression) is typically used to ensure that an AS that has connections to 2 separate Autonomous Systems (ISPs, typically) does not act as a transit AS and allow routes advertised by one ISP to be advertised over to the other.
So, AS 100 has a BGP connection to AS 200 and AS 300. As 300 advertises prefixes to AS 100, but AS 100 makes sure that it does not pass those routes, and instead advertises ONLY the local prefixes, as Jon pointed out.
HTH
Victor
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