nanog mailing list archives
RE: BGP Transit AS
From: "Michael K. Smith - Adhost" <mksmith () adhost com>
Date: Thu, 20 May 2010 12:49:54 -0700
-----Original Message----- From: Rafael Ganascim [mailto:rganascim () gmail com] Sent: Thursday, May 20, 2010 11:25 AM To: nanog () nanog org Subject: BGP Transit AS Hi all, I have a doubt about the bellow scenario, where the ISP1 use eBGP sessions to its peers and is a BGP Transit AS. NSP 1 ------------------ ISP 1 Router2 ----------- NSP 2 | | | | | | | annunce /21 | | | Customer1 --------------- ISP 1 Router1 announce /20 The "Customer1" is client on both ISPs (ISP1 and NSP1) and have an /20 IP prefix. To NSP1, it announce two /21 prefixes. To ISP1, it announce a /20 prefix. If traffic comes from NSP 2 (connected only to ISP 1) to Customer1, the ISP 1 Routers try to send data over NSP 1, ignoring the Custormer1->ISP1 link. To solve this question, an solution that I found is filter Customer1 prefixes in BGP session between NSP1 and ISP1 Router2. But this don't appear scalable... Is this solution right ? What is the better solution for this scenario? How large ISPs solve this kind of problem?
The more specific /21's are winning over the /20, so they will always be preferred by default. If you want to change that, you could announce the /20 to NSP1, or announce the /21's to ISP1. Mike
Current thread:
- BGP Transit AS Rafael Ganascim (May 20)
- RE: BGP Transit AS Michael K. Smith - Adhost (May 20)
- Re: BGP Transit AS joel jaeggli (May 20)
- Re: BGP Transit AS Ingo Flaschberger (May 20)