Hairpin NAT issue

RouterOS General
1

I’m having an issue with what I suspect is a hairpin NAT issue. A client requested moving an e-mail server onto a subnet with an existing e-mail server and the two aren’t able to communicate with each other.

Server 1 : 10.0.0.15/24
Server 2 : 10.0.0.77/24

Noteable interfaces are as follows :

Eth1 : 192.168.0.0/24
Eth3 : 10.0.1.0/24
Eth6 : 10.0.0.0/24
Eth13 : WAN

Note : Eth1,3 and 6 are bridged together

My masquerade rules are as follows :

/ip firewall nat
add action=masquerade chain=srcnat dst-address=10.0.0.0/24 src-address=\
    10.0.0.0/24
add action=masquerade chain=srcnat out-interface=ether13

This does not appear to work. Can anyone see the flaw in my logic?

2

On which addresses are the servers trying to communicate with each other? If they were communicating via the 10.0.0.X/24 addresses the router would not be in path as the devices could communicate directly.

3

Both servers are on the Eth6 interface. The issue (I believe) is that the mail servers are looking to an external DNS to resolve the mx records. When one server e-mails the other it’s like the first mx record (which is on the same subnet as it) doesn’t even exist and it goes straight to the second mx record.

4

Looks like you need to pin down which addresses the servers are attempting to connect on.