How do you determine where attempts to access a DC are coming from?

attempts are being made to access a DC.  See attached.  How can I determine where these attempts came from?

J.R. SitmanIT DirectorAsked:
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Brian McDonaldIT ManagerCommented:
I'd try a DNS lookup to determine the IP and trace it through the network to an endpoint
Brian McDonaldIT ManagerCommented:
Looks kind of like a brute force, might be an infected machine on the network?
J.R. SitmanIT DirectorAuthor Commented:
can you walk me through doing a DNS lookup?
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Brian McDonaldIT ManagerCommented:
The computer making the attempts will be listed in the security log on the DC
Brian McDonaldIT ManagerCommented:
open a command prompt on the DC and type


a new prompt will show up

now type in the computer name making the attempts

an IP will be returnednslookup
Brian McDonaldIT ManagerCommented:
J.R. SitmanIT DirectorAuthor Commented:
The computer making the attempts is the same computer it is trying to access.  Nslook up shows the correct IP of the DC
J.R. SitmanIT DirectorAuthor Commented:
I am running a virus scan now
Brian McDonaldIT ManagerCommented:
I'd look in the security log to confirm, the traffic looks like its not resolving the caller when it says "from *" its trying to logon to the domain so it makes sense the DC would be listed in the entry. Check the log and look for the logon type of the user.

Do you have any outside resources like Webmail or a VPN?

These entries could show up if an outside resource that uses AD authentication was getting hit on the web. In that case you'd have to close off the access to the resource with a firewall, etc. It doesn't necessarily mean something is on your local network. I see this traffic a lot when people try to brute force a vpn or OWA for example.

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J.R. SitmanIT DirectorAuthor Commented:
I looked at the log and all the Audits are Successful.

I did have an installation of SqlServer 2014 fail today.  Could it be related

We do not have Webmail or a VPN.
Brian McDonaldIT ManagerCommented:
Successful in the log just means it was able to audit the event. You need to look for the failed logins with logon type 3 (network logon) and find the caller computer name.

The speed of the requests and there variation look a lot like a brute force dictionary type attack. What other resources are on site that could be compromised? You could also run wireshark on the DC to find the IP requesting the traffic or start unplugging network ports until the traffic stops.

Are you sure there are no web visible access points to your network? a website with a login, etc? that would be using the DC for authentication?
J.R. SitmanIT DirectorAuthor Commented:
I did check the audit events for failed logins, however, I will check it closer.

Honestly, I have no idea if there are any visible access points.  I know all our wireless routers are secure.  

I do have Wireshark.  Not too familiar with it.  Any advice will be appreciated on how to run it and test.   Thanks
J.R. SitmanIT DirectorAuthor Commented:
hopefully, you can help Thursday
Naveen SharmaCommented:
Do you have RDP open to the Internet?

If you think it's from the Internet, turn on full logging on the firewall policy for any remote access services and you may be able to identify source IPs.

If it's internal, maybe Wireshark on a mirrored switch port.

How to track the source of failed logon attempts:

Audit the successful or failed logon and logoff attempts in the network using the audit policies:
J.R. SitmanIT DirectorAuthor Commented:
I set up the GPO's.   All of the failed login attempts are coming from the computer that is trying to be logged into.  e.g. spcala234 is trying to login to spcala234.

What should I do next?
J.R. SitmanIT DirectorAuthor Commented:
I figured out how to use Wireshark.  However, with all the results it is displaying what am I looking for?
J.R. SitmanIT DirectorAuthor Commented:
Thanks.  We blocked port 3389 on the Firewall
Naveen SharmaCommented:
Glad to see your issue has been resolved.

Track the Source of Failed Logon Attempts:
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