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  1. Hey Rene,

    I have found one of Swisscom BGP router from that expressions:

    AS path access list 1
        permit ^$
        permit 650[0-9][0-9][)]$

    permit ^$ : I think this one is written for locally originating routes

    I can't get a meaning the last one's " [)] "section ? You have an idea?
    By the way ; these ip as-path access lists , bgp filtering commands just filtering the AS's that advertising from another BGP routers right?

    Deniz

  2. Hi Deniz,

    The first entry will match on prefixes that originated in this AS. The second one will match on everything that ends with 650XX). Anything in the 64512 – 65535 range are private AS numbers. The [)] is a bit strange, normally you use the [] for a range (like 0-9). I'm guessing that they use it to match on sub-AS numbers in a confederation? That's the only time you will see a ) in the AS path:

    https://networklessons.com/bgp/bgp-confederation-explained/

    Rene

  3. Hi Rene,
    Just looked at BGP looking glass server. How can one practice regular expression on this site? Thanks!
    A.

  4. Hi A,

    Most of the looking glass servers support regular expressions so that would be the best option to get some practice. If you want to practice this "locally" then I would configure some BGP routers and use route-maps for things like AS path prepending, this can be used as a nice simulation of the Internet.

    Rene

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