[c-nsp] Dual-homing without BGP

Justin M. Streiner streiner at cluebyfour.org
Thu Feb 16 12:40:41 EST 2006

On Thu, 16 Feb 2006, Vincent De Keyzer wrote:

>> Unless their /23 is portable space, you're first going to have to take
>> this up with T and N.  If instead it is within T's allocation, you're
>> going to have issues [to say the least] getting the /23 ripped out of T's
>> ASN.
> I'm N, so no trouble on that side :)
> T is already announcing the /23 specifically (on top of their /16)... excuse
> my ignorance, but what would be wrong with N announcing it too?

The origin information for that /23 becomes inconsistent when announced by 
two separate, disjoint networks.  This can make troubleshooting network 
reachability issues a real pain.

Also, NSPs generally don't like it when someone else announces (originates
an announcement - just propagating an existing announcemet is OK) chunks
of their IP space.  It's much cleaner to have the customer get an ASN and 
speak BGP with their upstreams.

The customer would advertise their /23 and either accept only a default 
route via BGP from each upstream (redundancy is pretty much 
primary-standby at this point) or a small set of routes from each 
provider, plus default, to allow for a little more control over path 
selection.  A 2600 series router should be able to handle this amount of 
BGP work without any issues.


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