[c-nsp] Multihoming

Justin M. Streiner streiner at cluebyfour.org
Mon Aug 31 16:43:21 EDT 2015

On Mon, 31 Aug 2015, Jason Berenson wrote:

> Was interested in getting any pointers anyone might have about multihoming. 
> I've got an ASN and am working on a /24 from ARIN now.  I was thinking about 
> a pair of Cisco 3560's one for each provider and I was going to take default 
> routes from each, one with a higher metric and announce my prefix over the 
> primary link and pad the secondary link.  No customer or full tables needed.
> I was thinking about vlan'ing each switch into half public half private side 
> also.  Any pointers or tips or recommendations would be greatly appreciated. 
> It's been a while since doing this type of stuff.

You might need to get your IPv4 space from one of your upstream providers. 
As far as ARIN is concerned, that well is dry.

You will also want to start giving serious thought to IPv6.

I don't know how well 3560s handle BGP, but if you're just taking default 
routes from your upstreams, the resource needs are pretty light.  As the 
other person who responded mentioned - 4-byte ASNs could be an issue as 

You can accept the default route from provider A with a default 
local-preference and the one from provider B with a lower local-pref.  For 
outbound advertisements, as you mentioned, you can prepend your AS a few 
times on your announcement to provider B.  You'll also want to run IBGP 
between the two 3560s.

When you say "half public, half private", can you clarify what you're 
trying to do?


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