RE: Static routes in an AS vs BGP advertised routes

If you are advertising a /24 through both ISPs in each city then you won't
need them to do anything special as routers always put the most specific
route in their routing table. If you are advertising specific /24s to the
ISPs and one of the peering links drop then that /24 will be withdrawn from
that ISP's table and henceforth to the internet making the only available
route your other ISP.

The problem is if they aggregate and advertise only a /19 instead of
individual /24s In this case you could:

- Ask the pulverized ISP to withdraw the aggregate in favor of the specific
- Ask your second ISP to advertise your specific /24 in that city

I'd choose the second option because if your first ISP was truly hit by an
asteroid they'll be spending too much time
a. Attempting to make people actually believe they were hit by a piece of
ancient space debris
b. Trying to recover their network
c. Working on an appropriate press release showing lack of fault and sorrow
for the loss of several competent engineers and d. All the surviving
employees will be trying to sign a bunch of book and movie deals about their
experience :>
All in all your second ISP will be better equipped to get your traffic up
and running.

Greg Pendergrass Manager of Operations

Better yet, advertise your own /19 aggregate, mark your /24's with
communities that mean to your provider that they shouldn't be propagated
outside of their network and their customers (if they can't do this, fire
them) to be a good neighbor by not polluting the global routing table with
unnecessary routes. Then when the asteroid hits, just pull down the /19
advertisement (or if you're lucky, they are so destroyed they won't get
the announcement out to the world anymore anyway).