ISP inbound failover without BGP

Vlade Ristevski vristevs at
Tue Mar 4 14:27:58 UTC 2014

I've been doing the suggestion below for many years using the IP 
addresses that Cogent gives us. All I needed to do is get  LOA from them 
and submit it to my backup ISP. I've never had an issue with my Cogent 
IP's *not* being advertised by my other ISP and I really don't think 
there is very much management overhead for the customer once this is 
setup. I have an SNMP based alerting system (Cacti) set up so I can be 
alerted if too much traffic ever "shifts" to the backup link.

The client getting their own ASN is the better way to go but you should 
be able to do the above until that comes through.

On 3/3/2014 10:20 PM, Randy Carpenter wrote:
> 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.


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