Trouble shooting assigning IP addresses



  • I've been trying to troubleshoot a home network problem.  In my day job, I'm an IBM z/OS system programmer with 30 years experience, so I'm used to tracking down problems.  This network issue has me stumped.

    I had an Airport extreme (5th gen) in my basement by my Comcast cable modem,  I had a second Airport extreme (3rd gen) two floor up in my office in bridge mood.  The Airport Basement was my DHCP router.  My home network is assigned th IP range 10.0.1.000 - 10.0.1.255.  My wired devices have DHCP reservations based on Mac address.  The open assignable range is 10.0.1.50 - 10.0.1.99.

    Now my issue.  I started to see addresses of 192.168.xxx.xxx pop up on my wired and wireless devices.  I Googled and saw where some Airport extremes would have inconsistent problems when assigning ip addresses.  So I wanted to change my network setup to eliminate the "Daddy it's not working calls".  At first I eliminated the Airport Office (3rd gen) and just used the Airport extreme (5th gen).  This did not resolve my problems.  So I looked into bringing another router to assign IP addresses.

    I used an old computer and built a pfSense router to handle IP assignment and put my Airport extreme (5th gen) into bridge mode, and moved it up to the 3rd level office.  I still have problems assigning the correct 10.0.1.xxx addresses on my wired and wireless devices

    One of my wired Epson printer would not accept the 10.0.1.xxx address which should have been assigned by DHCP reservation, so I manually set the address.  On my wireless devices they will sometimes power up with a 192.168.0.xxx address.  The workaround it to turn off the wifi adapter, restart the wifi adapter and eventually you will get the correct address.  This happens even though the ssid network name is correct.

    One reason I went with pfSense is to gather network data for review, and I will scan the logs this weekend.  This weekend I also plan on powering down the entire house, and starting each device one at a time and verifying the address.  My last thought is trying a different wireless access device.  I would look for one supported by DD-WRT.  I like the simple interface to my Airport extremes, but it doesn't help when trouble shooting this type of problem.

    Any thoughts you have will be appreciated.


  • Rebel Alliance Global Moderator

    If you said your addresses your were getting were 169.254.x.x I would say they are just not getting an IP address from dhcp server and using APIPA

    But if your seeing 192.168.x.x – I have to assume you have another dhcp server on your network.

    Do you have a windows client, and ipconfig /all would show you who your dhcp server was.

    example

    IPv4 Address. . . . . . . . . . . : 10.56.41.224(Preferred)
      Subnet Mask . . . . . . . . . . . : 255.255.255.0
      Lease Obtained. . . . . . . . . . : Wednesday, February 12, 2014 9:56:06 AM
      Lease Expires . . . . . . . . . . : Wednesday, February 12, 2014 9:56:06 PM
      Default Gateway . . . . . . . . . : 10.56.41.1
      DHCP Server . . . . . . . . . . . : 10.56.144.20

    I am sure you can get the same info from a mac or linux box - just don't know the cmd off the top of my head.  You could always look in clients dhcp.lease file to see the IP of the dhcp server.



  • Working on my network ip addressing issue.  I shut everything down.  I brought up my internal wired network of  pfSense router, internal switches, appleTv units, printers and a couple of computers.  All Addresses were correctly assigned.  I released/renewed the ip addresses to check if the address assigned would remain correct, and this test passed.

    I then connected my cable modem to the internet, which connected with no problem.  I then again tested release/renew of addresses, and this test pasted with no problems.  And I had internet access.

    My internal network follows the 10.0.1.xxx address range.  I leave 20-99 open as my dynamic range, and assign my AppleTv, DirecTv, SlingBox, and MacMini server to static addresses via MAC reservation.  All these are functioning correctly.

    Final test.  I add my Airport Extreme 5th gen, which is in bridge mode, with no guest network, and the light turns green.  I open up my MacBook, connect via WiFi, and the address is 192.168.100.34, not correct.  I turn WiFi on my MacBook off, then I turn it on,  after three cycles I get a correct ip address.

    I confirmed via airport utility my settings.  I see nothing to change.  I replace my Airport Extreme 5th gen , with my older Airport Extreme 3rd gen, and I once again get a 192.168.100.22 address which is not correct.  I cycle the WiFi setting in my MacBook and after a few cycles, I get a correct address.

    My DHCP server is an older Dell system running the linux based software pfSense.  I made this change after I started getting bad IP addresses from my Airport Extreme 5th gen.  My cable modem is a Zoom 5431J DOCSIS 3.0.  But my first test was verifying the assignment of addresses from pfSense, without the cable modem.

    I've powered off both Airport Extremes and have checked the settings.  Not sure what else I might try with these Extreme units.


  • Rebel Alliance Global Moderator

    I would turn off their DHCP servers ;)  Just because you use it as an AP (bridge mode) I would validate that its dhcp server is OFF.  Since when you connect them you start to get different IP address in the 192.168 range it is very safe to say that their dhcp servers are running.

    Or something else on your wireless network that gets connected when you bring up wireless with your AE are running dhcp server.  What does your client that gets the 192.168 address say his dhcp server is, where does he point for gateway/dns, etc.  If you know the IP address of the dhcp server, or where it points to for gateway this will most likely tell you the IP address of the dhcp server.  Now do a simple look at your arp table, normally arp -a and you will the mac of that IP, you can then look up the maker from the first 3 of the mac address.

    My guess would be your AE have the dhcp server running.



  • My Zoom modem didn't have weekend support, so on Saturday I went and got a Motorola SB6141. Since the change I have not had any problems with a rouge dhcp server assigning addresses.

    I don't know if the Zoom modem was my problem (the new ip addresses listed the Zoom as the server), but the upgrade to the Motorola cost $40. Maybe, you get what you pay for.