4. Do the telcos have permanent outlets?
I mentioned earlier that some hosting providers promote their neutrality and have a number of carriers pre-connected in their data centres. This is great, because the set-up time for a new link can be extremely short (the fastest I experienced was about 45 minutes – the ISP just had to do its change-management paperwork then light up a port on the switch in the demarc and we were on).
Even if the provider doesn't have “resident” telcos, though, ask them who's in there already. If your choice of telco includes some that already have a presence in the data centre, this is another way to get the set-up time down relative to a supplier that has to dig a cable into the road and establish a presence in the data center.
5. ISPs vs resellers
For fear of sounding boring by referring back to hosting providers that have resident telcos, I'm going to do precisely that. When your hosting provider tells you that you have a choice of 30-odd service providers, does this mean they have 30 sets of equipment from 30 different telcos? Of course not. They probably have no more than a dozen actual ISPs, with the others' services layered on top as a simple reseller agreement. So if you're looking to take internet bandwidth under this type of scheme, consider who the actual provider is and maybe even spend a little more to get closer to the actual bandwidth provider.
6. Local-loop providers
Whatever type of connectivity you're putting into the datacentre, be it internet or private circuit, consider the actual provider(s) which will be providing it. For example, I once installed a circuit into a premise in north London and discovered as part of the process that the last kilometre and a bit was provided by BT rather than the provider I'd contracted with: COLT. The reason was that COLT's native network didn't extend that far, so they used BT for the last mile – the “local loop”.
The same applies to data centres, no matter how carrier-neutral they are: if they're not “on net” for a particular provider, then you'll have someone else providing the last mile. So if you're giving yourself resilience by running connections from two different providers into the hosting centre, you'll be upset if the last mile of both comes from the same exchange belonging to the same underlying provider.
Sometimes this can't be avoided (I've done installs in more than one city where there's been a single monopoly provider) but in such cases you need to at least work with the providers to ensure that your two diverse links come from different exchanges and enter the building through different road routes and entry points.
7. Provider blacklists
From time to time, a hosting centre may blacklist a telco. It's not common and I've not seen it personally, but in the old days I heard anecdotal examples where the hosting company said: “Sorry, we don't allow X in here” – generally because they were small cowboy outfits who were a pain to deal with and brought undue risk. By their nature you shouldn't be using small cowboy outfits anyway, so this shouldn't be a problem.