I work for a small company that hosts many of our own web sites.
Occasionally, our internet access goes out, and thus our sites go
down. What I am looking for is a way to create some kind of failsafe
or redundant internet connection that we can host our sites from in
the case of our primary connection failing. An instantanious and
automatic solution would be best.

First, let me describe our situation. We have 2 T1 lines at our
building. The first T1 line has 16 IP addresses allocated to it, all
of which are in use, and most of them are associated with a domain
name from one of our hosted sites. The second T1 line has only 8 IP
addresses, and is currently not being used. All of our computers are
running Windows 2000 Server, or Windows XP Professional. All the
computers are joined to an NT network domain.

I am looking for answers to the following questions:

1. How can we create internet connection redundancy for all of our
websites? Please take into account the difference in IP addresses
between the two internet connections, the fact that one connection is
using more IPs than the other other connection has allocated to it,
and the DNS changes that must take place for a site to change from one
IP address to another. If possible, I am looking for an automatic and
instantaneous solution. When our primary connection fails, I would
like people to immediately be able to access our sites via the
secondary connection. If this is not possible, please describe the
next best thing. If specific equipment is needed to address this issue
(eg an advanced router, or load-balancing equipment or software),
please describe that in your reply.

2. If the above is possible, I would also like to know if it is
possible to load-balance traffic between the two internet connections.
If so, please describe how this may be done.

3. Is there a better solution to internet connection redundancy than
having dual T1 lines? Would it be best to have some other kind of
connection? Perhaps wireless or satelite?

Please be as detailed as possible as to any configuration settings,
equipment, architecture changes, software, or similar things needed.

That's nice to know, but I'm really looking for an in-house solution.
I don't think large sites like Ebay or Amazon load-balance with a 3rd
party site. Thanks anyway.

There are a few different ways to load balance. If you can get
multiple nics in each of your servers, you can connect one nic to the
router for one t1 and the other for the router for the other t1,
giving each multiple ips. Then in the dns settings you can have
multiple A entries. This will enable round robin dns. Basically, every
other request for web services will come on one ip and every next
other request will come to the other ip. This has its drawbacks, which
is basically if one internet connection goes down, then it could take
2 or 3 tries to bring up your web site initially, though this is not
as bad as a total failure.

You mention you have 2 t1's, but you don't say who provides them. If
they are from different providers, you could apply to have an
atonomous systems number (AS#) and run border gateway protocol on your
router. This in effect would give you a single ip space for both t1
lines and would advertise to your isp your available ip's. Somewhere
up the line in the BGP router world, your providers routers would know
how to get to your ip space, and if one route went down they would
pick the other one. This has a few drawbacks as well, particularly
securing the AS# and the portable ip space from ARIN, which usually
drags its feet on such things. Also configuring BGP is no easy task. I
took a full year of coursework to become a cisco certified networking
associate, and we didn't even touch BGP. They get into that in the 2
year cisco certified networking professional coursework.

If you have two t1s from the same provider I'm sure you can work
something out with them to load balance your connection via a routing
protocol that allows for load balancing of equal cost paths, or a
stateful protocol that routes the traffic to the other pipe when one
goes down. The key here is for them to co-operate in updating their
routing tables, which shouldn't be hard if you are buying 2 t1's from
the same company.