Moving from one static IP to another without disturbing mailflow (onsite exchange)

[evilsatan]

I have thought this through and think I have got the plan right but wanted to confirm. I have an office which is currently on ADSL, a separate VDSL line has been installed and I have been sent the BT Openreach VDSL mode. There is already a Draytek 2850n router which has an integrated VDSL modem which will be used in the end.

The plan is to leave the Draytek connecting to ADSL on WAN1 for now as that is all set up and works with the existing IP which is used in the domain DNS. I was going to connect the VDSL modem to WAN2 and set that up as load balance, always alive. Now I should have 2 different static IPs for the office, I plan to update the domain MX records to point to the new static IP address which should mean that mailflow is consistent as both WANs should be active. Once the DNS has propagated I will set up WAN1 as VDSL and disconnect the ADSL altogether. I have cloned the open ports for the server to WAN2 so should have no issues there.

Does this setup work? i.e. will mail flow in fine on both IPs?

Cheers

[AD]

It should do as long as both MX records are active. We have done similar for fail over connections with Draytek routers.

[evilsatan]

My hope is that I can persuade them to move to a hosted exchange solution, if I can't then I will be setting up hosted backup MX servers for if their WAN/server goes down.

In this case I am not planning to keep using both IPs, my main concern was that when I update the IP on the MX records that mail will still flow, I thought it would as the office effectively has 2 IPs now but didn't want to go gung ho and mess it up!

[evilsatan]

A further thought on this before I make the changes at the weekend. How is mail handled once it reaches the IP? i.e. an email is sent, the MX record directs that to an IP, when it reaches the other end does the router forward ports to the exchange server? The setup is a dual-WAN Draytek router providing WAN to the server which is a DC and Exchange server (SBS 2011).

I have cloned the open ports for the SBS from WAN1 to WAN2, I can't see any other settings that would affect traffic to the server but just wanted to make sure so when I change the MX records to the new IP there will be no loss of service. I may add an MX record with a lower priority with the WAN1 IP just in case. The plan is to get the new IP live so WAN2 can become WAN1 and all traffic is over fibre rather than ADSL.

Cheers

[AD]

Ports to be forwarded are 25(smtp), 53(dns).

You might need to update your dns on your server if needed.

[evilsatan]

25 is already forwarded but 53 isn't, I assume if it isn't forwarded already and it is working on the existing IP then nothing further needs to be done?

I think I am over complicating things for myself here as essentially the only change to the system is the WAN IP, in my mind as long as I have the same ports that are forwarded now, forwarded for the new WAN then once the MX records are updated to the new WAN IP I should be set. Have I missed anything glaringly obvious? I can't see that the change of WAN IP means anything has to be altered on the internal server, just external domain DNS and router port forwarding?

Thanks

[AD]

Unless your original Wan IP was static and that was registered on your MX then your good to go.

[evilsatan]

The original WAN was static (as is the replacement WAN) but I was going to update the MX records to reflect the new IP. I assume not, as it would make no sense, but I don't need to update any DNS records on the DC that has the exchange server on too do I?

[MartinC]

Sounds like a solid plan to me, but one thing i would suggest if the router lets you do it, don't go down the "load balance" route, as i have seen things happen like the new line is not working correctly but you do not notice as half the traffic is going through the old route, i would set it to some sort of priority and have the other as a backup, that will it will stop completely and be more easy to spot and resolve. Nothing worse than losing lots of email before you know something is wrong.

[evilsatan]

Thanks mate, load balance is just until the VDSL becomes WAN1, then its moving to failover with a satellite as WAN2 The first step was to direct the mail to the new IP over a weekend and then I will switch the WANs within a day or two and remove the load balance. Their existing connection is shocking for the office size!