Fail-over

Norman Zhang norman.zhang at rd.arkonnetworks.com
Wed Feb 23 02:36:13 UTC 2005


Boyack, Kurt wrote:
>>I've a dual WAN router, currently some of my servers are bound with 
>>static IPs to ISP1. I like them to remain available on ISP2 if ISP1 
>>goes down. Do I need dynDNS service for this? Or I can type in 2 
>>different IPs for 1 serivce.
>>
>>e.g.,
>>
>>1.2.3.4 IN www.example.com #ISP1
>>2.3.4.5 IN www.example.com #ISP2.
>>
>>But internet may still resolve to 1.2.3.4 despite ISP1 being down. May 
>>I ask what the best way to go about this?
> 
> BGP is usually done between competing ISPs. You set up BGP to each ISP
> individually. They don't have to work with each other.
> 
> You can have two A records in DNS, but if someone tries connecting to
> the un-routable IP address it will fail. They will have to try again and
> they could end up getting the same IP address again. They will have to
> keep trying until they get the routable IP address. You will also have
> to either use NAT for one of the addresses, or have both addresses on
> your server (which might cause other problems). DNS caching could cause
> problems too. You would have to have a low TTL, which could put a heavy
> load on your DNS.
> 
> Note that if you do have two A records for a server like in the example
> above, it would balance the load over your ISPs and an ISP outage would
> not affect as many users.

Thanks for your explanation. I'll investigate into that. I'm wondering 
can this be done with dynDNS?

Regards,
Norman Zhang



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