Changed cable modem - now having LAN DHCP problems



  • I changed out my cable modem yesterday to an Arris SB6190 model. Most of my network came back up just fine, but some random devices are grabbing a 192.168.10.xxx address instead of the 192.168.1.xxx that they should grab. What am I doing wrong?

    Thanks!


  • Rebel Alliance Global Moderator

    You have some other dhcpd on your network handing out 192.168.10 address space.. I have a 6190 modem.. Is default dhcpd when wan is not available is 192.168.100.x, how would that possible even be connected to your lan devices anyway..

    You have this right
    internet -- modem --- pfsense --- switch - lan

    So these are different layer 2, so how would your modem be handing out dhcpd to clients? And again .10 is not the network it hands out .100 is.. So look to see what on your network is handing out dhcp.

    Your clients should tell you from what dhdpcd they got their address from..

    Windows do ipconfig /all

    DHCP Server . . . . . . . . . . . : 10.56.12.68

    Then look in your arp table arp -a for that IP. Ping it if you need to to get it put into your arp table. If that .10 was typo and you meant .100 then you have a cross over between your layer 2 wan network and your layer 2 lan network.. And your modem doesn't have a wan connection. When cable modems do not have a wan connection they often hand out dhcpd so you can get to their interface at 192.168.100.1 to help see what the problem might be.



  • @johnpoz said in Changed cable modem - now having LAN DHCP problems:

    You have some other dhcpd on your network handing out 192.168.10 address space.. I have a 6190 modem.. Is default dhcpd when wan is not available is 192.168.100.x, how would that possible even be connected to your lan devices anyway..

    You have this right
    internet -- modem --- pfsense --- switch - lan

    So these are different layer 2, so how would your modem be handing out dhcpd to clients? And again .10 is not the network it hands out .100 is.. So look to see what on your network is handing out dhcp.

    Your clients should tell you from what dhdpcd they got their address from..

    Windows do ipconfig /all

    DHCP Server . . . . . . . . . . . : 10.56.12.68

    Then look in your arp table arp -a for that IP. Ping it if you need to to get it put into your arp table. If that .10 was typo and you meant .100 then you have a cross over between your layer 2 wan network and your layer 2 lan network.. And your modem doesn't have a wan connection. When cable modems do not have a wan connection they often hand out dhcpd so you can get to their interface at 192.168.100.1 to help see what the problem might be.

    It's definitely .10 ... the first thing I noticed it on was the Unifi 24 port switch and the Unify AC Pro WAP. I am somewhat leery of that Unifi switch anyhow... I suspect it may be the culprit. I just could not figure out what would trigger it to act up like this when I changed the cable modem.

    I will try ipconfig/all and see what comes up. I may also buy a new switch and see if that makes a difference.


  • Rebel Alliance Global Moderator

    Their switches could be capable of running dhcpd I guess - but most of them are layer 2 so it would be a bit odd. Again look on a client - what does it show for the dhcp server?

    They normally run their dhcp server on say one of their USGs Or their egdgerouter - what switch switch model exactly?

    https://community.ubnt.com/t5/UniFi-Routing-Switching/DHCP-Server-in-US24-Switch/td-p/2103272

    According to this there is no dhcpd on their switches... As I thought.. Again what does one of your clients that got this 192.168.10 address show you as its dhcp server?



  • @johnpoz said in Changed cable modem - now having LAN DHCP problems:

    Their switches could be capable of running dhcpd I guess - but most of them are layer 2 so it would be a bit odd. Again look on a client - what does it show for the dhcp server?

    They normally run their dhcp server on say one of their USGs Or their egdgerouter - what switch switch model exactly?

    https://community.ubnt.com/t5/UniFi-Routing-Switching/DHCP-Server-in-US24-Switch/td-p/2103272

    According to this there is no dhcpd on their switches... As I thought.. Again what does one of your clients that got this 192.168.10 address show you as its dhcp server?

    It is a model 'Switch 24'. Right now the only things latching onto .10 are the Unifi switch, a Nest thermosat, that I am aware of. The Unifi WAP went back to .1 after a hard reset. I tried the same reset on the switch, multiple times with no change.


  • Rebel Alliance Global Moderator

    dude the switch can not run a dhcpd... So it aint the freaking switch!!!



  • @johnpoz said in Changed cable modem - now having LAN DHCP problems:

    dude the switch can not run a dhcpd... So it aint the freaking switch!!!

    I am not saying that it is the switch, just that it is the only device that has not let go of the .10 address.

    The ONLY thing that changed in this equation is the CABLE MODEM ... this setup has been stable for a couple of years until the modem was swapped, that's when the .10 showed up sporadically on the LAN. Most of the affected devices have been able to grab a .1 address after a reset of some sort, EXCEPT THE FREAKIN SWITCH.
    geez


  • Netgate

    Diagnostics > ARP Table

    What MAC address is ARPing for the .10 address? Look up the OUI? What manufacturer is it? Find the device. Unplug it.

    If that doesn't help, look at the switch mac-address-table. What port is that MAC address connecting through. Trace the cable. Unplug the device. (If the unifi switch lets you do such black magic)



  • @derelict said in Changed cable modem - now having LAN DHCP problems:

    Diagnostics > ARP Table

    What MAC address is ARPing for the .10 address? Look up the OUI? What manufacturer is it? Find the device. Unplug it.

    If that doesn't help, look at the switch mac-address-table. What port is that MAC address connecting through. Trace the cable. Unplug the device. (If the unifi switch lets you do such black magic)

    I do not see the MAC address (of the switch) in the ARP table. When I run the Unifi Controller software the switch still shows to be at the .10 address. I cannot ping the switch at that address. The Unifi WAP had previously shown to be at another .10 address in the controller software... after a hard reset of the WAP it is showing to be at a .1 address and I can ping it etc, etc. The same is true for a handful of other IoT gadgets around the house that showed (through their own menus and displays) to be grabbing a .10 address... a reset/reboot managed to get them back on the .1 address.


  • Banned

    This post is deleted!


  • @nadeemabasa said in Changed cable modem - now having LAN DHCP problems:

    I have same issue but now i got the solution from here.

    What was the solution?


  • Rebel Alliance Global Moderator

    There is not - he is just a spammer..


  • Rebel Alliance Global Moderator

    You have a dhcpd running!! Find it... Run dhcpdump or sniff for the traffic.. Pfsense can do a packet capture on its lan and you will see the broadcast traffic..

    And your cable modem is on a different layer 2.. Is it not??? Do you have your cable modem connected to your switch? Normally you would set your infrastructure devices to be static IP.