Windows 10: "Can't reach default gateway" and "DHCP server not found"

I can't connect my computer to the internet via my office WiFi. It's able to connect to the WiFi but then says "no internet connection" and "can't reach default gateway" and "DHCP server not found". Other people's devices in our office are able to connect to the internet via our office WiFi though, only my computer is affected. My computer is however still able to connect to the internet via my personal mobile hotspot, just not when using the office WiFi.

:)

 

Windows not using default DHCP gateway

On our subnet we have 2 routers one on 192.168.0.251 and a back one on 192.168.0.1. Computers (vitual Windows Server 2016/2019 and physical Windows 10) are configured via DHCP to use 192.168.0.251 as the gateway and "ipconfig /all" displays this in the "Default Gateway" field. However when I do a "tracert 8.8.8.8" on any of these computers they show the first hop as 192.168.0.1. Note also the the network troubleshooter reports "not issues detected".

When manually entering the ip settings into the ipv4 properties of the network adapter the problem is fixed: the first hop of "tracert 8.8.8.8" is 192.168.0.251. This fixes the problem on both virtual and physical computers. Also note that "ipconfig /all" still displays 192.168.0.251 as the "Default Gateway".

So why isn't the computer using the default gateway configured by the DHCP server (192.168.0.251) and switching to the backup router (192.168.0.1)? What makes the computer decide that the DHCP configuration can be altered to use the backup router (192.168.0.1) even when the "Default Gateway" still shows 192.168.0.251?

 

Windows not using default DHCP gateway

There is only one DHCP server on the subnet: 192.168.0.201

There are two routers on the subnet: 192.168.0.1 and 192.168.0.251

The computer’s ipconfig with manual IP address is:

Link-local IPv6 Address . . . . . : fe80::47b4:e819:2459:e0ac%12

IPv4 Address. . . . . . . . . . . : 192.168.0.5

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . . : 192.168.0.251

Then tracert returns:

Tracing route to dns.google [8.8.8.8]

over a maximum of 30 hops:

1 6 ms 4 ms 4 ms 192.168.0.251

2 etc



The computer’s ipconfig with automtic IP address is (identical):

Link-local IPv6 Address . . . . . : fe80::47b4:e819:2459:e0ac%12

IPv4 Address. . . . . . . . . . . : 192.168.0.5

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . . : 192.198.0.251

Tracing route to dns.google [8.8.8.8]

over a maximum of 30 hops:

1 1 ms 36 ms 30 ms 192.168.0.1

2 etc

I have found that when specified manually "route print" shows extra information that is not included for automatic IP configuration:

Persistent Routes:

Network Address Netmask Gateway Address Metric

0.0.0.0 0.0.0.0 192.168.0.251 Default

So the question still remains, why doesn't the computer follow the default gateway assigned by the DHCP server? And why has this recently started happening?

To correct the problem I've changed the DHCP server:

Old:

003 Router 192.168.0.251

New:

003 Router <None>

121 Classless Static Routes 0.0.0.0 255.255.255.255 192.168.0.251

When I do this and perform an ipconfig/renew the results are:

Link-local IPv6 Address . . . . . : fe80::47b4:e819:2459:e0ac%12

IPv4 Address. . . . . . . . . . . : 192.168.0.5

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . . : 192.168.0.251

Then tracert returns:

Tracing route to dns.google [8.8.8.8]

over a maximum of 30 hops:

1 6 ms 4 ms 4 ms 192.168.0.251

2 etc

The trouble with this solution is that some devices need the "Default gateway" setting to work and don't understand option 121 static route.

So why is the "Router" (Default gateway) DHCP setting seemingly ignored by the client computer?

 

Cannot Contact DHCP Server (Solved)

The speeds in many areas have been impacted because with everyone being at home practically 24 x 7 and using the internet, the infrastructure in many areas is being pushed to the limits.

As for not being able to to reach your DHCP, there are some things to try:

Start by running these two commands:

ipconfig /release all
ipconfig /renew

Then, run ipconfig to see if you have received a valid address and default gateway. If that does not work, post back and we'll go to the next steps.