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Re: Enterprise Multihoming
At 4:06 PM +0000 3/12/04, Stephen J. Wilcox wrote:
Hoping that I don't sound too much like Bill Clinton, that depends on what you mean by "it." If "it" is multihoming, with your own ASN, to two providers, your raise some valid points.I think its too easy, thats the problem.
Is there an intermediate alternative before you go all out? Yes, I think so, assuming your current provider has multiple POPs. Let me examine some of your points if we consider RFC 1998-style multi-POPping (I just invented that highly technical term) using PA address space.
For <$1000 (excluding bandwidth/ccts)Alternatively, another POP link, and preferably another router. If you are more concerned with loop failures than router failures, not a completely unreasonable assumption, you could get away with one router that has multiple interfaces, and spend some of the savings on backup power -- possibly a backup power supply in addition to the UPS, such as a Cisco RPS on their smaller routers. While you'll probably take a performance hit, or if you can reduce to critical traffic on an outage, you might get away with a second smaller router.
Like everything else, It Depends. My experience is that access links fail more often than provider routing systems, especially with a clueful provider. Since you can't guarantee that your physical connectivity to two different ISPs doesn't involve a shared risk group in the lines, there are still some things you may not be protected against.
One option, depending on the plant in your area, is that if you are considering a second router, consider putting it in a nearby building, reachable by WLAN (if you are minimizing costs), where that building minimally has different ducts to the telco end office, and ideally goes to a different end office. Not always possible, but to be considered. Longer-range wireless (radio or optical) links get more expensive.
That's a motivation for PA address space, where the provider aggregate is less likely to be small and easily damped.
so youAgain looking at intermediate solutions, there are always partial routes such as customer routes of the provier.
Again, an operational advantage of multiPOPping and working with one carrier, although you aren't going to be protected against insanity of their BGP/
MHO would be to look at "multihoming" as a spectrum of solutions rather than a binary choice of single-provider-single-link versus multiple-provider. In given situations, you might also want to look at DSL or cable for diversity, tunneling to an ISP since the broadband provider is unlikely to be willing to speak BGP. Even dialup/ISDN, sometimes for critical workstations, has its place.
Shameless plug: I do go through these options in my book, Building Service Provider Networks (Wiley). Even there, though, I only run through the alternatives. You will still have to make your own cost-benefit decisions based on business policy, budget, clue level and cost of alternatives.