Do your due diligence. Vendor-viability metrics include cash flow, cash burn rate, cash on hand and total debt. If you're unsure, consider including exit clauses triggered by indications of financial straits or missed SLAs (service-level agreements).
Another potential problem, especially if you go the well-known/small player route to save money, is that if you have two ISPs, and one of them accesses the Internet through the other, you are still dependent on one ISP. Before you sign up for a second provider, investigate its network design. If the provider shows any reluctance to provide this information, walk away.
Of course, using multiple ISPs is not without problems. For example, if you're using Internet VPNs, your best bet is to make one provider the primary ISP for all your locations. That way, there's no doubt about where to point the finger if user VPN connectivity goes south. It also means that, if your primary ISP offers various levels of IP-based QoS, you can reap the benefits. The higher class of service that you purchase for some of your packets with your lead ISP will be meaningless if your traffic traverses a second ISP link. Although having one ISP provide separate, redundant paths for your site will be less expensive than going with separate vendors, your eggs are still in one provider's basket.
Another point to consider when you use two ISPs is their willingness and ability to advertise your network. There is no guarantee that this will happen, especially if you have a Class C or smaller network. One way around this is to use one of the DNS-based route optimization products that we review in "Mapping Out the Best Route". These products require that you use multiple external addresses that are advertised by only one ISP.
If you decide to advertise your network via multiple ISPs, you will have to peer, or "multihome with," them via BGP, the routing protocol that runs the Internet. This means that you will have to buy routers that have sufficient memory and CPU stamina to process more than 100,000 BGP routes from each ISP. You also will need to have someone on staff, or a consultant, who understands BGP. These skills don't come cheaply.
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