On Wed, Sep 11, 2019 at 12:29:58PM -0400, Ross Tajvar wrote:
I'm curious how this works and why it's done this way. I have a friend who has transit from AS7922 (the remote AS in his BGP sessions are all 7922),
Are you sure your friend has transit from as7922? It sounds like your friend is buying from Comcast Enterprise (Ethernet Dedicated Internet), which places him on the regional CRAN network, not the 7922 national backbone (ibone).
but CenturyLink's looking glass shows an AS path of "33657 <his ASN>" and includes the no-export community. Why is the AS path rewritten? What is the design here?
IIRC, Comcast uses "local-as 7922" path rewriting for all enterprise EDI customers running BGP off of regional CRANs, unless I'm mistaken. So if your regional CRAN is as7015 (for New England), even if your physical circuit and BGP session land on a local SUR in your area, you have to use remote-as 7922 to setup the session with Comcast ENS, regardless of the fact that actual peer's router is using as7015. What Level 3/CTL looking glass is showing ("33657 <his ASN>") is most likely the true path reflecting of actual network topology behind the scenes. Your friend is connected to 33567/CRAN, not 7922/ibone. James