Hi all, I figured you guys were a great place to ask this question, even though it's not bird specific. If you have 2 discrete sites, both with BGP, one announces a 100.100.100.0/20, and another announcing 100.100.100.0/24, will traffic for the /24 block always go to the site announcing the /24, even if it's closer to the site announcing the /20? I was thinking that yes, it always routes to the shortest prefix, no matter the ping or number hops. And I was thinking that held true for ipv6, as well. A /32 and a /28 that cover the same range of addresses (the /32 being a subset of the /28) being announced from two different BGP sessions on two different networks, even if you are originating traffic from the same network the /28 is being announced on, and the /32 is a different network, so has additional hops and latency, any traffic you have going to the addresses in the /32 will go to the other network to go to the specifically announced /32. Thanks!
--On 28 June 2012 09:47:56 -0700 dspazman@epicup.com wrote:
If you have 2 discrete sites, both with BGP, one announces a 100.100.100.0/20, and another announcing 100.100.100.0/24, will traffic for the /24 block always go to the site announcing the /24, even if it's closer to the site announcing the /20?
The more specific route, if accepted, will always win, irrespective of any other consideration. This is true on both IPv4 and IPv6, and is fundamental to IP routing rather than specific to BGP. -- Alex Bligh
That is what I thought, but I had someone questioning me, so I wanted to make sure from the experts... ;) Thanks! -----Original Message----- From: "Alex Bligh" <alex@alex.org.uk> Sent: Thursday, June 28, 2012 10:00am To: dspazman@epicup.com, bird-users@trubka.network.cz Cc: "Alex Bligh" <alex@alex.org.uk> Subject: Re: Routing Question --On 28 June 2012 09:47:56 -0700 dspazman@epicup.com wrote:
If you have 2 discrete sites, both with BGP, one announces a 100.100.100.0/20, and another announcing 100.100.100.0/24, will traffic for the /24 block always go to the site announcing the /24, even if it's closer to the site announcing the /20?
The more specific route, if accepted, will always win, irrespective of any other consideration. This is true on both IPv4 and IPv6, and is fundamental to IP routing rather than specific to BGP. -- Alex Bligh
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Alex Bligh -
dspazman@epicup.com