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4201 posts

Uber Geek

# 239579 24-Jul-2018 20:42
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So I had a funny one today. Bit of back story first:


Client who we look after the broadband, voice, router, pabx for rang up complaining of having trouble connecting a new laptop to his network. I just checked basics, wireless key was good, lets try on ethernet cable, no good - probably a driver issue as everything else was operational on the network and router looked fine.


So he gets his "IT Guy" back who obviously mucked around for a bit... and then for god knows what reason, decided it would be a good idea to factory reset our router. It's a Mikrotik, so came up with the default config which of course didn't get it anywhere near operational, not too mention blew away the VPN config for his other site, our remote access etc...


I get the "IT Guy" to reconfigure at least the PPP interface so I can get in and get our config reloaded (thank god for scripted backups, albeit this one was getting to be close to a month old). Do all that and all good, phone system re-registers, PC's have internet access again, site-to-site VPN back up.


That was about a week ago.


Fast forward to today, and client rings again with complaints of file sharing not working, can't print blah blah blah. And, of course, it's all our routers fault!


He has his "IT Guy" on site who I have a conversation with and suggest perhaps was the windows server the thing doing DHCP for the network? My VERY limited Windows server knowledge made me ask does the server have the DHCP role installed (was I right?). So I suggested, lets turn off the routers DHCP server and see if you get one from the server. Now this is where I seriously began to question the "IT Guy's" knowledge as he then asked, how do I force the computer to get a new IP address?.... ummm do ipconfig /release and then /renew..... Like really? It doesn't give a new lease, so no worries, turn router DHCP back on.


But that leads to me my question, as I watched leases get dished out I see a whole bunch get given to the same MAC, and the hostname is the server hostname....



So my question... what's going on there?


I don't have to fix this, but it would just be good to know if I ever see it again.

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431 posts

Ultimate Geek

Emergency Management

  # 2061946 24-Jul-2018 20:50
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What version of server are they running?


Do you know if they have a direct access server or vpn client dial in server?

15205 posts

Uber Geek


  # 2061952 24-Jul-2018 21:15
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DHCP is a broadcast protocol - a request for an IP address etc is sent out, the first reply is the one used. If you have multiple DHCP servers the fastest / closest one assigns the IPs. If you have a large network you can have some IPs from your router, some from Windows.


Overlapping ranges / IPs can cause weird problems. Not sure if either of those are relevant as I don't have time to read your post in depth and think more right now sorry. I did a project around DCHP recently so I know a little, not as much as a Windows / network admin though - architecture level stuff.


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Uber Geek


  # 2061953 24-Jul-2018 21:23
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Hi as Justin says, I would suggest there is some remote access service happening.



3867 posts

Uber Geek

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  # 2062075 25-Jul-2018 10:21
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Looks very much like it's grabbing 10 addresses for RRAS


Here's a screenshot from a Windows DHCP server giving 10 leases to another server for RRAS purposes.


Information wants to be free. The Net interprets censorship as damage and routes around it.

4201 posts

Uber Geek

  # 2062117 25-Jul-2018 10:24
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Ahh very good. So normal behavior for a server with remote access users.


No idea on the server version sorry.


Like I said, not my problem to sort, but just wanted some more info as it seemed the "IT Guy" didn't really know what was going on.

3867 posts

Uber Geek

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  # 2062582 25-Jul-2018 20:56
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it seemed the "IT Guy" didn't really know what was going on.



There's a lot of that around sadly. Plenty of "IT guys" who have no bloody idea. 

Information wants to be free. The Net interprets censorship as damage and routes around it.

462 posts

Ultimate Geek

  # 2062814 26-Jul-2018 10:10
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Sounds a lot like he doesn't know what he's doing.




Another point worth noting is that DHCP servers on Microsoft servers will generally detect another DHCP server running on the same segment and stop the DHCP service on the server which needs to be manually restarted.





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