Static routes in an AS vs BGP advertised routes
Suppose you had a scenario where your AS is multi-homed to two ISPs in, for example, 8 cities around North America. Every site is connected to both ISPs and all of your address space occupies a /19. To your ISPs, you advertise specific /24s in each city. In turn, each ISP advertises your /19 to the rest of the Internet. Everything is going along smoothly until an asteroid crashes into the data center of one of your ISPs in one of the cities. It causes extensive damage and a certain amount of hysteria but to you, it means that only one of your ISPs can truly reach your full /19. That is, the /24 you were advertising in that city is now only reachable via one of the ISPs. But the ISP taken out by the asteroid is still advertising the full /19. Under the circumstances (loss of life, hysteria, sub-optimal routing), would it be appropriate to ask the unfortunate ISP to create a static route on their network to push traffic destined for that particular /24 over to the other ISP's network? This way, the /19 advertisements can be maintained and when traffic destined for that one /24 reaches the asteroid ISP, it can get passed over to the non-asteroid ISP. The route wouldnt be advertised to other carriers.....just used to make sure traffic reached the correct final destination. Will ISPs make these types of accommodations? Suppose the reason was less unexpected than an asteroid. For example, suppose you open a site in a 9th city, but only one carrier is available there. In other words, are ISPs reluctant to slap in static routes for every customer who comes along with some sob story about poor planning and/or unexpected growth? Your comments on this theoretical scenario are much appreciated. -BM
On Wed, 8 Aug 2001, Murphy, Brennan wrote: [snip]
of the ISPs. But the ISP taken out by the asteroid is still advertising the full /19.
Under the circumstances (loss of life, hysteria, sub-optimal routing), would it be appropriate to ask the unfortunate ISP to create a static route on their network to push traffic destined for that particular /24 over to the other ISP's network? This way, the /19 advertisements can [snip]
Of course, this would only be sure to work if the ISPs in question were peering. Otherwise, you could likely create loops. [snip]
Will ISPs make these types of accommodations? Suppose the reason was less unexpected than an asteroid. For example, [snip]
If they have just been hit by an asteroid, they might be worrying about more then adding routes for you, and may not do it in a timely fashion. Your immediate best course (best from the "you can only trust yourself" school of thought) would be to have an established way to control their advertisements (communities) and withdraw your /19 announcement from their network. For example, you could advertise both your /19s and your /24s, using communities to prevent route table pollution. After someone sets you up the bomb, you drop the one /19 advertisement, and potentially change the community on the surviving advertisements to keep some traffic flowing through that provider.
On Wed, 8 Aug 2001, Murphy, Brennan wrote:
Everything is going along smoothly until an asteroid crashes into the data center of one of your ISPs in one of the cities. It causes extensive damage and a certain amount of hysteria but to you, it means that only one of your ISPs can truly reach your full /19. That is, the /24 you were advertising in that city is now only reachable via one of the ISPs. But the ISP taken out by the asteroid is still advertising the full /19.
Under the circumstances (loss of life, hysteria, sub-optimal routing), would it be appropriate to ask the unfortunate ISP to create a static route on their network to push traffic destined for that particular /24 over to the other ISP's network? This way, the /19 advertisements can be maintained and when traffic destined for that one /24 reaches the asteroid ISP, it can get passed over to the non-asteroid ISP. The route wouldnt be advertised to other carriers.....just used to make sure traffic reached the correct final destination.
It's not only reasonable, but not uncommon. I've never heard of an ISP that's had an astoroid take out a POP refuse to make these accomodations. Frankly, though, I'd try to replace them with a provider that pays a little more attention to celestial traffic patterns. James Smallacombe PlantageNet, Inc. CEO and Janitor up@3.am http://3.am =========================================================================
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