On Tue, 30 May 2000, Harry Whitehouse wrote:
> Please excuse this off-topic question (and feel free to recommend any better
> suited lists).
>
> My firm has a single ISP (PSINET) and reliability has been reasonable over
> the years using their T1 service. But we have periods where customers can't
> ping us, or their tracerts show severe latency problems -- perhaps once a
> week. Often we "lose" an entire geographic segment for several hours.
>
> So I'm looking at adding a distinct, redundant ISP. But I'm uncertain how
> this works.
It's called multi-homing, and you'll want to run BGP4 and peer with
multiple providers.
> All my remote clients will be pointing to www.xyz.com. That will resolve to
> a single IP address, correct? But then how can one use multiple ISP's? I
> know this can be done, I just would like to understand how. An suppose one
> ISP's route is blocked, how does the client know to switch over to the other
> route?
BGP will fail over the route as long as you're authorized to advertise it
from multiple providers. Almost any good-sized provider (and PSI is
certianly big enough) will allow you to peer their address space with
another provider so long as it's pre-arranged. You'll need to get an ASN
from ARIN to do this, and again your provider is probably the best source
of help with this.
> Also, any suggestions on the hardware needed to pull this off on the "my"
> side would be appreciated. I've seen stuff like www.FatPipeInc.com which
> seems to address this issue.
*Lots* of memory in your router, and ask to carry full routes from each
provider you peer with. Also ask your provider to explain how the peering
works and what kinds of configuration things you'll be able to control on
your end without pissing either of them off.
There's a really good Cisco Press book called something like
"Internet Routing Architecture" that covers BGP fully if you want to
understand how it works.
I also like to order my circuits from different wireline carriers to each
ISP if that option is available in the area and doesn't just mean
someone's timesharing with the RBOC over the same lines.
Paul
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