Multi-master

[Pascal Nobus]

After 10 hours in the dark from our upstream-provider (the first time in 2
years), we were brainstorming on someting thas is called multi-master I
guess.

We are working together with another company which has another provider and
want to do the following.

For all our domains we mention 3 nameservers with the registry:
ns1.siteA primary on site A,
ns2.siteA secondary on site A,
ns3.siteB primary on site B (copy of ns1, done with rsync-over-ssh)

Normally the domains resolve all through CNAME to the name "webserverA".

When site A goes completely in the dark, we change the IP of "webserverA" to
an IP within the range of siteB.
If TTL is expired the domains will resolve to the IP of siteB (where there
is a copy of webserverA).

I don't expect it to work for 100%, but even if 80% is covered after 3
hours, we're saved.
And yes, it's better to have two providers with our own routers, but this is
not reachable for us.


But will it work?
And how low can I set the TTL?
Which nameservers do I mention in the zone-files?





Best Regards,
Pascal