Multihoming single server in DNS

[Spongy]

Hi,

I am installing a mail server for a client who wants a fail-over mechanism, so if the primary IP address goes down then the secondary IP (a cheap ADSL with static address) can be used with the mail service automatically. I am purchasing a dual WAN router,

How do I complete this in DNS? If I use the same MX priority it will create a round-robin and I don’t want to shorten the TTL of the MX records, as it feels like an ugly way of accomplishing what I want.

Normally I would do the following:

server.domain.com – A record – IP Address
domain.com – MX record – 10 – server.domain.com

How do I have to change this to get a multi-homed single server functioning in the case of the primary line going down? I did have a suggestion that I CNAME the A records and use those hosts with the mx’s, but I didn’t know exactly what and how that would help…

Thanks in advance,

Spongy

[Spongy]

Hi,

I could use priority MX records easily if I had more than 1 server, but I don’t – I am trying to multihome a single server.

As I said before, the way I would usually do it with one server, one IP is like this:

server.domain.com – A record – IP Address
domain.com – MX record – 10 – server.domain.com

With 1 server and 2 IPs, I have found it more difficult.

I can’t just add another MX record because then I won’t be specifying the backup IP anywhere and there would be no resolution.

If I specify the 2nd IP and domain like above then I have to use CNAMES to alias the server (because there is only 1 server), but you can’t use a combination of CNAMES and non-CNAMES in the same entry – so I can’t do it that way.

I can’t find anything in either ‘DNS and BIND’ or the ‘DNS Cookbook’ about this, so any information from anyone else would be great!

Thanks

[Author]

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