ISP inbound failover without BGP

Joe Greco jgreco at
Mon Mar 3 21:27:50 UTC 2014

> This may sound like dumb question, but... I'm used to asking those.=0A=0AHe=
> re's the scenario=0A=0AAnother ISP, say AT&T, is the primary ISP for a cust=
> omer.=0A=0ACustomer has publicly accessible servers in their office, using =
> the AT&T address space.=0A=0AI am the customer's secondary ISP.=0A=0ANow, i=
> f AT&T link fails, I can provide the customer outbound Internet access fair=
> ly easily.=A0 So they can surf and get to the Internet.=0A=0AWhat about the=
>  publicly accessible servers that have AT&T addresses, though?=0A=0AOne tho=
> ught I had was having them use Dynamic DNS service.=A0 =0A=0AAre there any =
> other solutions, short of using BGP multihoming and having them try to get =
> their own ASN and IPv4 /24 block?=0A=0A=0AIt looks like a few router manufa=
> cturers have devices that might work, but it looks like a short DNS TTL (or=
>  Dynamic DNS) needs to be set so when the primary ISP fails, the secondary =
> ISP address is advertised.

The usual solution is to get the public servers stuck in a colo that's

Most of the other solutions tend to be a bit dodgy.  If your gear is
sufficiently competent, you can hack up a solution with multiple 
addresses for each of the servers (one on each ISP) and then use a
short TTL to fail over, but this has more of "fail" than "fail over"
about it, because there are a bunch of issues that typically result.

... JG
Joe Greco - Network Services - Milwaukee, WI -
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

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