Fail-over

[Kevin Darcy]

Norman Zhang 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?
>>>      
>>>
>>Probably the best way to do this would be to do BGP to both of the ISPs.
>>With BGP, people will be able to get to your servers (with ISP1 IP
>>addresses) through ISP2 when ISP1 is down.
>>    
>>
>
>Thanks for your suggestion. I can't use BGP. ISP1 and ISP2 are 
>competitors. 8( Is there some way of doing this with BIND?
>
No good way, no. You could have a script automatically change the A 
record (Dynamic Update would probably be the cleanest way) if it senses 
a failure on the ISP1 connection. Unfortunately, you'd have to lower 
your TTLs to low levels -- perhaps anti-socially low levels -- in order 
to provide any kind of reasonable failover time for Internet clients.

The long-term solution is for browsers to use SRV records (think a level 
of indirection above A records, with preferences and weighting, or, if 
you prefer, MX records on steroids that aren't limited to mail 
exchange). But adoption of the SRV mechanism seems to be taking a long time.

                                                                         
                                          - Kevin