Enterprise Multihoming

Thu Mar 11 20:49:56 UTC 2004

John

As already stated by lots of folks on the list, this is largely a business 
decision rather than a technical one. However, there are some more useful 
thoughts:

1. Is the decision to multi-home consistent with your other redundancy plans?

For example, why go through all the trouble of multi-homing and setting up 
BGP, only for both circuits to be plugged into the same router? ..or, two 
routers but neither of them on UPS.

This is akin to insisting on a Class A bank-grade firewall but not 
bothering to put a lock on the server room door...

2. Multi-homing is usually considered critical when one is discussing 
hosting of some kind. Could you be served with multiple servers in 
geographically separate collocation centers inside one ASN?

While many MIS departments like to have direct access to their own servers, 
this can often be an emotional preference rather than a technical one. 
Often only the "public facing" servers need BGP redundancy. The back-ends 
can be set up to fail-over to separate VPN/IPs in separate ASNs.

Having said all that, I prefer physical access to my machines too. So I'm a 
hypocrite.

3. If you are not doing hosting, a two-ISP NAT solution may make more sense 
than BGP. In addition to burdening the global routing tables; good BGP 
management is expensive. It involves either hiring someone with the proper 
expertise/experience or purchasing that expertise. Relatively speaking, 
there are not a lot good experienced BGP admins out there.

4. What is the price of downtime, in real dollars? For many business, this 
really can be estimated. Consider lost time (wages, utilities, etc.) and 
lost sales. Then compare it to the various options.

Just my two cents,

John

At 10:04 AM 3/11/2004, you 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 systems and
>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
>our routers.
>
>I see a few upsides to this, but are there any real downsides?
>
>Flame on. :-)
>
>Thanks,
>John
>--