[NTLUG:Discuss] Multiple DNS records for POP3 and SMTP server?

[Chris Cox]

Neil Aggarwal wrote:
> Hello:
> 
> This document:
>  
> <http://www.barracudanetworks.com/ns/downloads/Barracuda_WP_MX_Load_Balancin
> g.pdf>
> http://www.barracudanetworks.com/ns/downloads/Barracuda_WP_MX_Load_Balancing
> .pdf
> gives a strategy for having multiple MX records to
> have redundancy for incoming email to get to my servers.
> 
> I don't see anything that talks about doing the same
> thing for pop3 and smtp connections.  
> 
> If I have multiple A records for these:
> 
>         pop3.JAMMConsulting.com A 1.2.3.4
>         pop3.JAMMConsulting.com A 5.6.7.8
> 
>         smtp.JAMMConsulting.com A 1.2.3.4
>         smtp.JAMMConsulting.com A 5.6.7.8
> 
> and then set Outlook (I use version 2003) to
> use pop3.JAMMConsulting.com and smtp.JAMMConsulting.com
> as its incoming and outgoing server, will Outlook
> whichever IP address is available if one of them
> is down?

DNS will do a simple round robin.  If you need
a true load balancing scenario (works for failover as well),
you'll have to look at balanceNG or something similar.
The problem with just using DNS is that your client
would have to know to make another request... which
might end up with the SAME one AGAIN... trial and
error (might not get the right one for some time).

In that scenario you have a "virtual" IP that sits in
front of the servers.

Also, Linux HA can do the virtual IP thing as well and
it can do failover (redirecting the virtual IP)... but
that would be more suited for servers actually running Linux.

I would examine balanceNG... I think it's probably more
what you are looking for.

If your company insists on a high cost solution, you
can purchase an F5.... but it's nothing more than
a poorly coded software load balancer IMHO.