Exchange Server 2007SP1 and IPv6 Issues

Our Exchange Server has been in production now for a week and there are some significant issues coming up that relate to speed. It appears that running IPv6 on this server creates a major speed issue. This could be seen in very slow client access (oftentimes you will see a message like “Trying to connect to Microsoft Exchange” and a user may even be prompted for their username and password) and the Exchange Management Console and Shell are also performing very poorly with waits up to several minutes to access information or initialise. However it is not as simple as turning off IPv6 on the network adapter as the result can be that the ExchangeTransport service will hang and crash. That was our experience this week. Our consultant had turned off IPv6 in the network adapter’s properties, but the next time the server was restarted, ExchangeTransport Service would not start and would usually crash every 5 minutes. This service is key to the Hub Transport role and your Exchange server will not be able to deliver any mail if it is not operating. Rechecking IPv6 on the adapter caused the problems of ExchangeTransport service to go away but the performance issues immediately returned.

Our next step to try (tomorrow probably) is to disable IPv6 outright as described in this MSKB article. Additional relevant information can be found here, here, here, here, here and here. This MSKB article is also very important because it details situations where the KB952842 article may be incorrect due to the roles in use on the server. It will be noticed that most of the articles referenced above are not concerned with performance, but with the ExchangeTransport service failure. I have not yet found very much about performance issues, but it seems highly likely this is the cause of our problems at the present time.