[c-nsp] internet redundancy

[Howard C. Berkowitz]

At 9:25 AM -0400 5/15/05, Kern, Tom wrote:
>I'm looking to set up internet redudancy.
>i have 3 internet connections in 3 diff sites. all sites are 
>connected via point to point T1's.
>Each site uses its own isp.
>I use eigrp internally.
>
>i assume I would have to call the isp's and use BGP to sucessfully do this?
>what would I need to set up on my end?

With three involved, that's really your only alternative. Do you have 
dedicated links between your sites, or would the failover be via the 
Internet?  In the latter case, how do you handle security? Encrypted 
tunnels? Of what sort?

>How complicated is this?

You will need to develop a routing policy and get your ISPs to agree 
to it. Once that is done, you will need an AS number, which, when I 
last looked, was $500 per year. One or more of your ISPs may be 
willing to help you get started, usually wanting to be preferred or 
charge professional service fees.

The next step is to develop your routing policy, which will depend in 
part on how you go site-to-site. You need at least one BGP-speaking 
router at each site, and you might have more than one to protect 
against failure.  At a minimum, have EIGRP default point at a BGP 
speaker.

Assuming you have permanent links between your sites, the minimum 
approach could be for each site to advertise its address space to the 
ISP, but to prefer the direct links for inter-site communication. 
 From each ISP, you could request full or partial routes, and share 
them by iBGP among your sites. Partial routes, for example, are 
usually the directly connected customers of that ISP.

Again, I'm assuming a lot here. It's not necessarily hugely 
complicated, but it's easy to make errors. Before I could design 
something, I'd have to know details including the nature and speed of 
your inter-site links, your backup strategy, if the ISPs are widely 
geographically distributed, etc.