Look at it this way:
If Multi-homing to ensure maximum reliabilty was not a good thing:
why would XYZ isp do it?
Take this example:
Remember last year (or year before?) when MCI had the routing issue
on the east coast? I had a friend that had 2 T-1's to MCI, he lost all reachability
for over 5 hours. I had another friend that had a T-1 from MCI and one from AT&T.
He stayed up, and so did his ecommerce site.
So the end questions is:
Do you trust your upstream enough to bank your business, or more importantly
your reputation as an IT professional, on the ability of everyone at your ISP
to maintain their network and everything that gives you access 99.999% of the time?
->From: firstname.lastname@example.org [mailto:email@example.com]On Behalf Of
->Sent: Thursday, March 11, 2004 11:41 AM
->To: John Neiberger; firstname.lastname@example.org
->Subject: Re: Enterprise Multihoming
->Mutli-homing a non-ISP network or system on multiple carriers
->is a good
->way to maintain independent links to the internet by means of
->peering, uplinks, over-all routing and reliability. My
->network on NAIS
->is currently multi-homed through AT&T. I use a single
->provider as both
->of my redundant links via 100% Fiber network. Even though this is
->cheaper for me, all it takes is for AT&T to have some major
->outage and I
->will be screwed. If I have a backup fiber line from say, Global
->Crossing, then it doesn't matter if AT&T takes a nose dive, I
->my redundancy there.
->That is why most non-ISPs hold multihoming via different providers as
->their #1 choice.
->John Neiberger wrote:
->>On another list we've been having multihoming discussions again and I
->>wanted to get some fresh opinions from you.
->>For the past few years it has been fairly common for non-ISPs to
->>multihome to different providers for additional redundancy in case a
->>single provider has problems. I know this is frowned upon now,
->>especially since it helped increase the number of autonomous
->>routing table prefixes beyond what was really necessary. It
->seems to me
->>that a large number of companies that did this could just have well
->>ordered multiple, geographically separate links to the same provider.
->>What is the prevailing wisdom now? At what point do you feel
->that it is
->>justified for a non-ISP to multihome to multiple providers? I ask
->>because we have three links: two from Sprint and one from Global
->>Crossing. I'm considering dropping the GC circuit and adding another
->>geographically-diverse connection to Sprint, and then
->removing BGP from
->>I see a few upsides to this, but are there any real downsides?