[nsp] Multihoming with Two ISP without BGP

[Kristofer Sigurdsson]

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