Fail-over

[Boyack, Kurt]

> >>I've a dual WAN router, currently some of my servers are bound with=20
> >>static IPs to ISP1. I like them to remain available on ISP2 if ISP1=20
> >>goes down. Do I need dynDNS service for this? Or I can type in 2=20
> >>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=20
> being down. May=20
> >>I ask what the best way to go about this?
> >=20
> > Probably the best way to do this would be to do BGP to both=20
> of the ISPs.
> > With BGP, people will be able to get to your servers (with ISP1 IP
> > addresses) through ISP2 when ISP1 is down.
>=20
> Thanks for your suggestion. I can't use BGP. ISP1 and ISP2=20
> are competitors. 8( Is there some way of doing this with BIND?
>=20
> Regards,
> Norman Zhang
>=20

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.