[nsp] Multihoming with Two ISP without BGP

Tue May 18 16:31:10 EDT 2004

The /28 problem aside, you could you BGP Conditional Advertisement.

http://www.cisco.com/en/US/partner/tech/tk365/tk80/technologies_configuration_example09186a0080094309.shtml

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....

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.

Thanking you

Regards,
chintan

----- Original Message -----
From: "Kristofer Sigurdsson" <ks at rhi.hi.is>
To: "Chintan Shah" <chintanshah.j at ddsl.net>
Cc: <cisco-nsp at puck.nether.net>
Sent: Tuesday, May 18, 2004 11:47 AM
Subject: Re: [nsp] Multihoming with Two ISP without BGP

Chintan Shah, Wed, May 19, 2004 at 12:00:06AM -0700 :
> Dear Kristofer,
>
> Thanks for your reply but I have still some doubt which are as 
> follows.
>
> 1. Upstream proivder for both ISPs are differents.

Well, at some point, they must come together in order for this to work, as most providers will not accept routes as small as /28 - they will simply use the less specific route, i.e. the traffic will go to the ISP whose address space this is (unless you are using PI address space or other specially reserved blocks, e.g. the old "ALLOCATED UNSPECIFIED" blocks).

> 2. Customer is having 16 IP - /28 block from both ISP
> 3. if let say ISP1 will announce the route on behalf of customer for 
> IP block of ISP2 and same ISP2 will do then from interenet two routes 
> will be to customer , which will be given preference to customer as 
> customer wants dedicated connection (BW) for each department.

You can use BGP communities or add to the AS path where the ISPs announce the routes.

>
> 3. which routing protocol should i run to stop annocuncing the route 
> from ISP to internet when connection will fail. How this will work , 
> if u can elaborate on this.

Well, any really.  For example, you could use OSPF or RIP between the customer and the ISPs.  However, this may not be desireable, as the customer will be able to do some damage...RIP might be a better choice, especially over serial links, but it does have slower convergence.  I'd recommend using another routing protocol than the ISP is using internally, or at least a different process (if applicable).

I'd use BGP; simply use a private AS number for the client...this will make things considerably easier.  It also means you don't have to redistribute between routing protocols, you simply peer all the way...

>
> Link should be utlized such way that in normal condition any request 
> from IPs (which allocated to Manufacutre department)  of ISP1 should 
> follow
path
> through ISP1 and same for ISP2.

This is extremely hard to guarantee, but if you announce the routes that way, most of the traffic will probably follow that general rule.

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

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