Posted on 2006-06-10
Medium Priority
Last Modified: 2008-01-09
Experts; we are facing a problem with our Exchange Infrastructure; we have 3 Windows 2003 Active Directory Domains in 3 different cities [i.e. city A, city B & city C];

--    city A consisting the abc.com Root Domain
--    city B consisting the def.abc.com Child Domain
--    city C consisting the ghi.abc.com Child Domain

 all of them Inter-linked to each other in one forest each domain having;

--    1 Domain Controller
--    1 Exchange Server

Now the problem is not actually in the configuration of either the ADS or the Exchange; these cities are inter-connected through Wireless based WAN links & these links are not stable most of the times due to which the Active Directory Replication & the Exchange Replication mostly fails & this causes the emails to hang in the queues especially for the exchange server in the abc.com domain; due to which 9 out of 10 times we have to restart the server in order to push the mails in the queues.

My questions are the following;

1 -    How can I customize the replication in such a way that even if the WAN links are not stable the emails should not stop in the queues ?
2-     How can I know the replication dependencies for the exchange server for abc.com ?
3-     In the scenario that I have described; what is the best practice that we can implement in order to be sure of maximum UP time for the email flow ?

Kindly provide me with a detailed solution to my problem.
Question by:hanisaif
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Expert Comment

ID: 16877183
The SMTP service will try to connect to the destination server. If it cannot get there (because the wireless link is down at that moment) then the message will go back into the queue and wait for some set amount of time before it retries. That time may be 5 minutes, an hour, or some other amount of time. If you turn down that time interval, it will retry more often, and maybe get a chance to send when the wireless is back up again.

Your problem isn't with Exchange or AD replication. There is no software setting you can change to make it fix your link problems. You just need to fix your wireless link so it doesn't go down all the time. I know that 802.11b equipment can push over 30 miles with the right antenna and AP.

Author Comment

ID: 16884849
Thank you for the response, I think I didnt put my question properly; the distance between;

--    city A & city B is 400 miles
--    city A & city C is above a 1300 miles
--    city B & city C is 1000 miles

so which means that these Wireless Links are being provided by our ISP, now mainly the problem we are facing is with the Exchange Server for the abc.com domain this server is hosting more than 150 user's mailboxes, & another problem that I have noticed is that even though we have individual Internet Conneciton for all these three locations the exchange server for the domain abc.com even stops or fails to send emails to other domains such as hotmail.com or yahoo.com or gmail.com; the emails start queueing up in the queues & once we restart the server only then the emails are pushed otherwise 9 out 10 times they would remain in the queues, now I have done some diagnostics on the server for the domain abc.com using DCDIAG tool from Microsoft & the server passes successfully on all the tests but I am unable to understand that if everything is OK then why this is happeing almost every 3 days. On every reboot the third day when the server starts giving problems after check the Event Viewer I find errors such as;

"The Knowledge Consistency Checker (KCC) has detected that successive attempts to replicate with the following domain controller has consistently failed.
Domain controller:
CN=NTDS Settings,CN=EX-ISAV-CENTRAL,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=extra,DC=com
Period of time (minutes):
The Connection object for this domain controller will be ignored, and a new temporary connection will be established to ensure that replication continues. Once replication with this domain controller resumes, the temporary connection will be removed.
Additional Data
Error value:
1727 The remote procedure call failed and did not execute.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp."

& this error is logged multiple times unless I do a reboot for that server.

I hope you get a better picture of the problem now.


Author Comment

ID: 16926993
Experts; please give me a solution to this problem; the last comment I posted was on 06/12/2006; after that I didnt get any reply from any side, I need your support please.
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Expert Comment

ID: 16928309
If your shortest link is 400 miles, that tells me it isn't a end-to-end wireless link. If you are having uptime issues on your link, then there is nothing that AD or Exchange can do to fix that.

AD and Exchange don't care if you are on wireless or any other type of connection. It just sends packets to an IP address, and expects they get to the other side. If it stops getting acknowledgements that data was received on the other side, then it figures the link is down, and it will retry again later.

You can play with the time interval on retries. You can force a connection to a server in Exchange. None of this will fix your problem though, they are just workarounds.

Here's something to try. Go to a command line and type:

ping far_away_server -t

just specify the name or IP of a server at the far end of one of these links. After it runs for a few hours, do a CTRL-C and see what % of the packets were lost. If it reads 1% or more, you have definately got link issues.

Author Comment

ID: 16929366
Thanks for the reply; but now my question here is that once the link is back UP, the server still doesnt starts sending emails to the local domains; & also as I explained previously that each location has its own Internet Connection then why even the external emails on the server in city A start hanging in the queues; this is happening only with this server; the other two servers are not having such problem, they keep sending emails to the internal domains except the one in city A & also sending emails to the Internet is not an issue for these servers as well, whenever is reboot that server the other two exchange servers automatically start sending emails to that domain without needing to reboot, & only after rebooting the server the queues for the Internet emails are cleared.

I suspect there is a problem with this server; but cant figure out what it is... could anyone please give me a procedure where I can be able to at least troubleshoor the problem.

Expert Comment

ID: 16929777
Let me see if I understand this now, you have one server at one office that has this problem. At this office, the link to the Internet is different from the link to the other offices?

Well instead of restarting the server, try just going into Exchange System Manager, in to the Queue, finding a domain that has messages waiting, and "Force Connection" on that domain. If it delivers the messages, then you know you are fighting a retry interval type of thing.

If that doesn't do anything, try stopping and starting just the SMTP service, or all the Exchange services. If you can narrow down your work around, it will help you get closer to a solution.

Author Comment

ID: 16930177
Thanks for the comment; but all of the things that you have mentioned I have tried them all; like for example I have tried to Force the connection on the queues for the Internet email, it doesnt work, I have tried to restart the SMTP service alone & then with all the Exchange Services but it doesnt work, & you are right that this location has its own Internet Connection but from the same ISP.

Expert Comment

ID: 16931517
I think I'm out of ideas then. There has to be something that the restart is doing that can also be done manually without a reboot of the box.

You might want to put up a new pointer question to draw more attention to this question.

Author Comment

ID: 16932899
The only thing I see everytime I reboot is that under Directrory Service in the Event Viewer I see an entry logged that says;

The Knowledge Consistency Checker (KCC) has detected that successive attempts to replicate with the following domain controller has consistently failed.

& then it mentions the name of the server in city B; this is an indication for me that I need to reboot the machine. I have tried it several times to avoid rebooting; but it doesnt help.

Could you be more specific about putting a new pointer question.

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