North American Network Operators Group

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Re: multi-homing fixes

  • From: Alex Bligh
  • Date: Sat Aug 25 14:34:47 2001

Do you *really* want your DNS TTL set down in the same range as
the time for a BGP route fall-over?
Q: what is the route convergence time of 'the internet', for any
  given route? It is certainly larger than BGP route fall-over

DNS may well not be an ideal protocol for doing this [1]. However,
as Howard eloquently posted earlier, I was rather evidencing that
BGP isn't the only tool available, and is certainly not the only
tool possible. Heh, may be we'll have to go do some work on a new
one, or enhance a current one.

[1] = you may well find that client stacks are a larger problem.

We usually run with hign TTLs, and drop them down before impending
changes.  Unfortunately, there's no easy way to do that 24 hours before
the backhoe gets there...
So you /could/ always run it low. Look at technologies like
ultradns / nominum, to see how this can actually work well.
And feed that database (far easier distribution problem) from
your reachability information.

Also, if you run and drop your DNS TTL, I *do* pay,
because now my DNS server has to hit the network for a look-up for
your site - you just added several packets to the transaction.
Ummm, so if X is accessing Y's site, Y pays for some of the network
costs, and X pays for some of the network costs. However, at least
in this proposal Z (unconnected 3rd party) doesn't suffer - he does
suffer from routing table bloat.

The suggestion that the users (both source and destination) should
pay for performance, rather than the rest of the internet in general,
is, of course, shocking to some :-)