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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: BGP Path Filtering
On Thu, 15 May 2003, Mark Radabaugh wrote: > > I'm having a hard time finding best practices for filtering outbound bgp > announcements when providing transit to bgp-speaking customers. While we > currently multi-home to several providers it appears we will soon need to > provide transit for customers with their own AS's. > > I find lots of references (and understand) the basic > > ip as-path access-list 3 permit ^$ > > and it would seem that should we wish to provide transit for a bgp customer > AS12345 we would use: > > ip as-path access-list 3 permit ^12345$ > > but I think this breaks if AS12345 prepends their advertisement. yes it will > Next up is: > > ip as-path access-list 3 permit ^12345_[0-9]$* > > Which seems correct to me. Is this still best practice (or even correct)? no, perhaps you mean ..[0-9]*$ but that still wont allow multiple prepends as it wont match the space only the numbers try ip as-path access-list 3 permit ^(_12345_)+$ which will allow one or more of their as's ASN is pretty crude tho, consider using a prefix list to filter each prefix and include length Steve > > Mark Radabaugh > Amplex > (419) 720-3635 > > >
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