[117423] in North American Network Operators' Group
Re: Multi-homed implementation and BGP convergence time
daemon@ATHENA.MIT.EDU (Seth Mattinen)
Fri Sep 11 18:58:06 2009
Date: Fri, 11 Sep 2009 15:54:37 -0700
From: Seth Mattinen <sethm@rollernet.us>
To: nanog@nanog.org
In-Reply-To: <OF346C9852.A522194D-ON8625762E.00712E9A-8625762E.0072DE58@securian.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Andrew.Claybaugh@securian.com wrote:
> Hello - my company currently has two connections with a single tier 1 ISP.
> We are using the AS from our ISP at this time. In the next month we will
> be implementing a third connection with a second tier 1 ISP, so we will now
> be using our own AS number on all three routers. My question is when we
> implement the new connection and update our existing connections to use are
> own AS number, how much downtime will there be? So far the second ISP has
> only said that it could be hours for BGP to fully converge. We are looking
> for more detail about how long the outage will be and how widespread.
Hours? No way. It's more like minutes.
> Will it be relatively short to our customers that are on one of the ISPs we
> are directly connected to? Is downtime less for customers on other tier 1
> ISPs versus tier 2, etc. ISPs?
Doesn't matter.
> We will only be receiving a default route on each of the three connections.
> Our routers will be advertising a small number of routes - 6 to 8.
>
I strongly encourage you to reconsider and take more than a default if
you're multihoming and your routers have enough memory. Remember to
create a full mesh on your BGP routers.
And as already said, if you're totally new to BGP and multihoming, hire
someone with experience in such matters to set it up.
~Seth
