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Exchange 2003 - Firewall logs Port 6004 Outbound

Posted on 2014-01-08
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Hi Experts,

We have an Exchange 2003 environment and we have firewall logs filling up with denies from some of the Exchange 2003 servers showing connection attempts to remote servers in the LAN on UDP 6004.

Over the last month or so, another team has introduced an Exchange 2010 servers, to allow them to move to Office 365.

There's no correlation between the destination IP of the connection and the Exchange 2010 servers either.

Any ideas why these servers have started to attempt to connect to other devices on 6004?
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Question by:MarkMichael
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by:Alan Hardisty
ID: 39764772
That port is used for RPC (RPC via HTTPS or Outlook Anywhere as it is known in Exchange 2007 and up).

Are you using a Front-End / Back-End environment with multiple back-end servers?
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by:MarkMichael
ID: 39764778
Yep, thats right.

We have several back ends and several front ends for Exchange 2003.

This has been set up like this for a few years and the firewall logs have only recently started getting huge, with all these additional denies in it. I'm curious to figure out what could have changed to start this...

This is an example of the firewall log:

08/01/2014 10:42:15:FWSM-4-106023: Deny udp src exchange:10.45.140.22/24474 dst inter:10.181.16.20/6004 by access-group "acl-exchange" [0x70dc7886, 0x0]
08/01/2014 10:42:15:FWSM-4-106023: Deny udp src exchange:10.45.140.22/24473 dst inter:10.172.232.20/6004 by access-group "acl-exchange" [0x70dc7886, 0x0]
08/01/2014 10:42:15:FWSM-4-106023: Deny udp src exchange:10.45.140.22/24472 dst inter:10.45.157.252/6004 by access-group "acl-exchange" [0x70dc7886, 0x0]
08/01/2014 10:42:15:FWSM-4-106023: Deny udp src exchange:10.45.140.22/24469 dst inter:10.173.50.248/6004 by access-group "acl-exchange" [0x70dc7886, 0x0]
08/01/2014 10:42:15:FWSM-4-106023: Deny udp src exchange:10.45.140.22/24468 dst inter:10.243.34.35/6004 by access-group "acl-exchange" [0x70dc7886, 0x0]
08/01/2014 10:42:15:FWSM-4-106023: Deny udp src exchange:10.45.140.22/24467 dst inter:10.45.156.20/6004 by access-group "acl-exchange" [0x70dc7886, 0x0]

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by:Alan Hardisty
Alan Hardisty earned 500 total points
ID: 39764832
So presumably your front end server is 10.445.140.22 and the backends are 10.181.16.20 / 10.172.232.20 / 10.45.157.252 / 10.173.50.248 / 10.243.34.35.

If that is the case, I would allow the port as it is internal and needed for RPC to work happily.
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by:MarkMichael
ID: 39764861
The 10.45.140.22 is one of the backend servers.


The addresses: 10.181.16.20 / 10.172.232.20 / 10.45.157.252 / 10.173.50.248 / 10.243.34.35 - are all Workstations of users from around the globe in different offices.
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Alan Hardisty earned 500 total points
ID: 39764864
Ah - okay.  Are the client computers configured using RPC over HTTPS?

If they are, then they will need to communicate with the server.

Have a read of the technical description on this page for info:

http://www.pc-library.com/ports/tcp-udp-port/6004/
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by:MarkMichael
ID: 39765459
Cheers for the link.

I understand both ways would be required to allow the connection to have 2 way communications between a frontend and backend server (between RPC Proxy and DSProxy).

Although the connection appears to be being initiated from the Exchange server, to these workstations, which I find concerning, as Outlook surely wouldn't be listening on UDP 6004 anyway?

Thanks for your help Alan,

Cheers, Mark

Ps. I'm getting confirmation whether these machines are configured for RPC over HTTP.
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