[SOLVED] set IPv4 default gateway for connection

[ruthless]

this sounds simple but I seem to have a persistent default gateway and I can't manage to change it. I have been using the laptop on my home network with no problems. But when I connect to the new network it uses the old default gateway and therefore can't see the correct nameserver. I have no access to the router.

[ruthless]

I would like to set the default gateway with the network connection editor if possible. But it seems that's not the case.

[GreyGeek]

The default gateway (192.168.x.x) is set by the router manufacturer.
Some routers, in the "DHCP Settings" option, allow you to change the "Device IP address", the device being the router, hence the gateway address. In that same dialog is usually the beginning IP address for dispensing and the concluding IP address for dispensing. I have mine set for 192.168.1.100 to 105, which allows all the internet devices to be attached, and no others. That dialog also typically allows the gateway mask to be set. Mine is 255.255.255.0 (/24), which fixes the first three octets. Also on that dialog (at least on mine) is the IP address lease time.

If you don't have access to your router you cannot change any of these settings. My ISP has a web app which allows me to access my cable modem with the login name (usually "admin") and password, usually a long number. These are often found on the back, under the chassis between the box and its foot rest, or on the underside of the lid which requires you to remove it to see the login info.

[claydoh]

Wifi, wired?
What 'new' network?
A different location, or your home one has been changed?
You can iirc only change the gateway if you set things up manually, instead of Automatic (DHCP)


if it is wired, have you tried creating a new connection, maybe?
If the new location is not using automatic addressing (DHCP) you may well have to ask whoever is in charge of the router/networking/IT department.

Without knowing more details, it is harder to give advice.

[ruthless]

it is WIFI and I have no access to the router people .. none. I don't know if it is using DHCP .. but I do know what the default gateway and the DNS server and search domain should be. I have configured these into the connection using IPv4 parameters in the connection manager. all that is left is to change the default gateway from 192.168.0.254 to 10.1.10.1 but I have not been able to do that yet. the default gateway can be checked using IP ROUTE.

[oshunluvr]

Well, AFAIK, NetworkManager or systemd-neworkd handle that for you for WiFi unless you've set your connection to a fixed IP setup. This is set in /etc/netplan. My desktop, systemd-networkd with fixed IP contains:

# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s31f6:
      dhcp4: no
      dhcp6: no

bridges:
  br0:
    interfaces: [enp0s31f6]
    addresses: [192.168.1.199/23]
    gateway4: 192.168.1.1
    nameservers:
      addresses: [8.8.8.8,8.8.4.4]
  parameters:
    stp: true
    forward-delay: 4
  dhcp4: no
  dhcp6: no

While my laptop has only:

# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: NetworkManager

My server is more complicated...

[ruthless]

my laptop has the same netplan code as yours. what confuses me is .. somewhere .. I believe the address 192.168.0.254 is hard coded. the network manager on the laptop is using this address as the default gateway for the WIFI connection. this was correct for my home network but does not work for the new public network I want to use. My question is: where is the laptop getting the 192.168.0.254 value from and why not from DHCP? I thought maybe I could override this value in the Network Manager nmconnection file .. but was not able to that either. Weird and frustrating.

[oshunluvr]

What do you have in /etc/NetworkManager/system-connections/ ?

Maybe just clearing it will allow it to resume normal operation,

[oshunluvr]

Or how about adding this to your netplan file:

  wifis:
    wlp3s0
      dhcp4: yes

Obviously, replace wlp3s0 with your wifi adapter name.

[ruthless]

here is the system connection file. note the hardcoded DNS values which are correct. the DHCP is not working and I have zero communication with the router people.

[connection]
id=SSID
uuid=4461bd8e-ed13-48f2-9c4a-4da89923b198
type=wifi
permissions=user:ruthless:;

[wifi]
mac-address-blacklist=
mode=infrastructure
ssid=SSID

[wifi-security]
key-mgmt=wpa-psk
psk=********

[ipv4]
dns=75.75.75.75;
dns-search=hsd1.fl.comcast.net;
ignore-auto-dns=true
may-fail=false
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=
method=auto

[GreyGeek]

https://forums.xfinity.com/conversat...375f08cde06033

[ruthless]

I just needed to put all my findings together to fix this. the DNS was done in the connection settings. the default via needed to be done on the command line. but this was lost every time the computer woke up. so I found documentation and wrote a service to call a script which fixed it. yes I am a developer but not much linux experience

[Snowhog]

I just needed to put all my findings together to fix this....I found documentation and wrote a service to call a script which fixed it. yes I am a developer but not much linux experience

What documentation?
What service did you write?
What script?

[ruthless]

it is a systemd service that calls a script that adds the correct default via gateway using the route command. the script uses nmcli to make sure which connection is active and not run on all connections. The IPv4 DNS server was added by editing the connection via connection manager. I wrote the script and the service.

the service looks like this. it calls the CONNECTION script in the home directory every time a WIFI connection is made .. which was needed when the laptop woke up after the lid being closed.

[Unit]
Description=connection service
Requires=network-online.target
After=network-online.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/home/CONNECTION.sh

[oshunluvr]

Thanks for posting your solution, it may help someone else someday.