[SOLVED] Some devices not showing in DHCP.

Aug 30, 2019
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Hi,
my father has a small office with local network. And suddenly some of the devices can't access network.

It looks like this:
There is a telephone line with ADSL
Line is connected to Zyxel vmg8324 (Modem/Router/Wireless AP)
Zyxel has 4 LAN ports

LAN1 - PC1 connected (it works fine)
LAN2 - TP-link simple desktop switch connected - switch has two devices: PC2 (works fine) and credit card machine (doesn't have access to LAN)
LAN3 - TP-link simple 8-ports switch - 3 devices attached (1 credit card machine, 2 printers) - none of them has access to LAN
LAN4 - free port

There are several phones connected through WLAN.

On my DHCP table I can see just PC1, PC2 and these wireless devices.

I didn't have much time to see everything. I just printed network status from one of the LAN-printers and it had IP starting with 169.x.x.x which was strange to me (it had 10.0.0.x before).

This problem occured suddenly, without us making any changes in LAN environment.

What should I check first? What could be the problem?

Regards,
Bartek
 

Ralston18

Titan
Moderator
What make and model is the LAN printer with the 169.x.x.x IP address?

Any chance that someone factory reset the printer?

Likewise for the router. Devices such as credit card machines and printers should have static IP addresses assigned via the network router and those static IP addresses need to be outside of the allowed DHCP IP address range. The static IP addresses should also be reserved in the router via each respective device's MAC.

Sketch out a simple network diagram of the office showing all devices and connectivity. Look for some common path between the devices that cannot access the network and the router.

Label the devices and also note their DHCP or static IP addresses. Subnet masking is important also. All should be 255.255.255.0

May be just a faulty failing cable, loose port connection, etc..

And you do not need to be secretive about the IP addresses within your network. Private networks all share one of three IP address ranges. What you do not want to reveal is your Public facing IP address: what your ISP assigns to your router.

Reference:

https://www.lifewire.com/what-is-a-private-ip-address-2625970

Feel free to google for other similar readings....
 

Ralston18

Titan
Moderator
What make and model is the LAN printer with the 169.x.x.x IP address?

Any chance that someone factory reset the printer?

Likewise for the router. Devices such as credit card machines and printers should have static IP addresses assigned via the network router and those static IP addresses need to be outside of the allowed DHCP IP address range. The static IP addresses should also be reserved in the router via each respective device's MAC.

Sketch out a simple network diagram of the office showing all devices and connectivity. Look for some common path between the devices that cannot access the network and the router.

Label the devices and also note their DHCP or static IP addresses. Subnet masking is important also. All should be 255.255.255.0

May be just a faulty failing cable, loose port connection, etc..

And you do not need to be secretive about the IP addresses within your network. Private networks all share one of three IP address ranges. What you do not want to reveal is your Public facing IP address: what your ISP assigns to your router.

Reference:

https://www.lifewire.com/what-is-a-private-ip-address-2625970

Feel free to google for other similar readings....
 

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