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BGP and null path announcement

http://info.connect.com.au/docs/routing/general/multi-faq.shtml

((How do I configure BGP so that bad things don't happen?))

Does the command "ip as-path access-list 1 permit ^$" from the link above, stand for a null path (^$) ?

2 REPLIES
Purple

Re: BGP and null path announcement

Yes.

The regular expression ^$ matches the empty string.

This is useful when matching on prefixes that are locally generated within an AS. They will carry an empty AS-PATH until they leave the AS. Therefore, ^$ can be used within an as-path access-list to match on locally generated routes ...

Hope that helps - pls do rate posts that help.

Regards,

Paresh

Re: BGP and null path announcement

Hello,

basically this allows to sort out those routes learned from another AS. It is the easiest and most flexible way of preventing to become transit AS between two ISPs for a customer.

The statement would allow only those routes to be announced, which are locally originated within the customer AS.

Hope this helps! Please rate all posts.

Regards, Martin

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