Several of our new Exchange servers are failing to relay messages because it is communicating over IPv6 and not matching any receive connector I previously set up. I'm not sure how we are using IP6 since we only have a IPv4 network and we are routing across subnets.
I discovered this by typing helo in from the source to the server that is confused by my IP6 address. I saw the IPv6 message and the custom message I gave this receive connector. (connectors with more permission have a different helo)
220 HUB01 client
helo asdf
250 HUB01.nfp.com Hello [fe80::cd8:6087:7b1e:99d4%11]
More info about my environment:
I have two dedicated Exchange forests each with a distinct purpose. They have no trust and only communicate by SMTP. They both share the same DNS infrastructure via stub zones.
What are my options? This is my guess, but I'm no IPv6 expert so I don't know which one is the best option
- Disable IPv6
- Add the IPv6 address to the whitelist (isn't that IP dynamic?)
- Tell Exchange to use IPv4 instead
- Figure out why we are using IPv6 instead of IP4
Best Answer
Your servers must be on the same subnet,as they are using link-local IPv6 addresses to communicate, and probably multicast DNS to do name resolution. IPv6 is always preferred over IPv4 when it is found to be working on Windows 2008 or later servers, and it is enabled by default.
You can disable IPv6 to get rid of this, but you would be better off actually implementing IPv6 if you can. The world is out of IPv4 addresses, in case you haven't heard.