Honestly? Because the end-customers are not technically competent enough to run dual-homed BGP, and we don't want to be their managed service providers on the IT side. And announcing the AT&T space is fine until something goes wrong, and I have to troubleshoot the problem (Customer - "How come AT&T is down, and we're not getting inbound traffic to our servers?", and I discover L3 or CenturyLink isn't accepting my advertisement for some weird reason, but they won't fess up to it for a few frustrating hours)
________________________________ From: Randy Carpenter <rcarpen@network1.net> To: Eric A Louie <elouie@yahoo.com> Cc: NANOG <nanog@nanog.org> Sent: Monday, March 3, 2014 7:20 PM Subject: Re: ISP inbound failover without BGP
Is there some technical reason that BGP is not an option? You could allow them to announce their AT&T space via you as a secondary.
-Randy
----- Original Message -----
This may sound like dumb question, but... I'm used to asking those.
Here's the scenario
Another ISP, say AT&T, is the primary ISP for a customer.
Customer has publicly accessible servers in their office, using the AT&T address space.
I am the customer's secondary ISP.
Now, if AT&T link fails, I can provide the customer outbound Internet access fairly easily. So they can surf and get to the Internet.
What about the publicly accessible servers that have AT&T addresses, though?
One thought I had was having them use Dynamic DNS service.
Are there any other solutions, short of using BGP multihoming and having them try to get their own ASN and IPv4 /24 block?
It looks like a few router manufacturers 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.