[nsp] Multihoming with Two ISP without BGP

[Kristofer Sigurdsson]

Jack.W.Parks at alltel.com, Tue, May 18, 2004 at 03:31:10PM -0500 :
> The /28 problem aside, you could you BGP Conditional Advertisement.
> 
> http://www.cisco.com/en/US/partner/tech/tk365/tk80/technologies_configuration_example09186a0080094309.shtml

Good idea...

> 
> Jack
> 
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Chintan Shah
> Sent: Wednesday, May 19, 2004 2:36 AM
> To: Kristofer Sigurdsson
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [nsp] Multihoming with Two ISP without BGP
> 
> 
> Dear Kenith,
> 
> Now, I almost go your all points suggested by you  and below my conclusion and understanding from your suggestion , if any of my conclusing direct me in wrong path , please correct.
> 
> 1. So, ISP1  has to redistribute the Routing protocol ( either OSPF or RIP
> which is running between ISP and customer)  to   BGP and also have to
> prepand the AS path for IP block of ISP2 as per your advise and same for ISP2
> 
> 2. So, whenver ISP1 links fail then routing protocol will not converged and ISP1 will stop to do announcing as redistrubuting the routes and don't getting any routes.
> 
> 3. Now, prepanding AS-path as per you suggestion will keep dedicated line for both department as per customer requiremet.
> 
> Now, only one doubt which still i'm not able to get:
> 
> A.  This is true that /28 will not be accepted on intenet by most of providers and then how this problem will be resolved by co-ordinating with both ISP as both ISP doing peering with two different international upstream provider.. if u can give some more idea please....

You'll have to co-ordinate this with your ISP's upstreams, their upstreams, etc. until you find a point in which those providers are peering, somehow,
in order to be able to do this.  The trick is to find a provider in the "normal" way the traffic flows to deliver the traffic to the other
ISP.

Internet -> <Less specific route> -> PROVIDER -> <more specific route> -> ANOTHER PROVIDER -> ...and so forth...

> 
> B.  you have also indicated to use Private AS number and BGP at customer site , how it will work as has to do peering with two Different ISP which has got public AS and customer will have private AS.

This works  - but when the ISPs announce the routes, it's better if the refrain from announcing a private AS in the AS path, as that
could result in problems. :)

-- 
Kristófer Sigurðsson			Tel: +354 525 4103 / MSN: ks at rhi.hi.is
Netsérfræðingur/Network specialist	Reiknistofnun HÍ/University of Iceland