Re: Strange cabled network fault when rebooting from Windows (any version) into Ubuntu 24

Java Jive <[email protected]> wrote:

> VanguardLH wrote:
> 
>> Don't know what are the "networking problems".  In each scenario, can
>> you connect to the internal web server in the cable modem, router, or
>> whatever you have upstream of the problematic host?  Check if you can do
>> intranet connections before testing if you can get to the Internet.
> 
> I can't connect to anything in the problem scenario of rebooting from 
> Windows into Ubuntu 24, I can connect to everything when there is no 
> problem.

While the following are Windows/DOS commands, there is probably
something very similar for *NIX:

ipconfig /release
ipconfig /release6
ipconfig /flushdns
ipconfig /renew
ipconfig /renew6

That will do a soft reset of the NIC.  All bindings are released, and
then renewed (reinstated) for both IPv4 and IPv6 (the command args
ending with "6").  The DNS flush is optional.  A cold reboot (not a warm
reset) will send a reset signal to the NIC, and other hardware, to put
them into a known initialized state.  A warm restart does not.  Perhaps
the above (but in *NIX commands) might reinitialize the NIC.  If the
commands work, you could have them run at startup.

For the above renew commands to work means your computer must be able to
reach the upstream DHCP server to get its IP binds from there.  However,
if you configured the OS to use static IP addresses then the computer
isn't getting IP binds from the upstream DHCP server.  The same for DNS
server assignment unless the NICs (IPv4 and IPv6) in the OS config are
configured to use specified DNS servers.  In the past, I configured the
hosts to use DHCP IP assigned, but configured the router (in the cable
modem) to assigned static IP addresses based on the MAC of my hosts.  I
wanted some intranet hosts in one subnet, and others in a different
subnet, and then blocked one subnet from another (to keep the family
from getting at my host).  By using static IP ranges for its DHCP
server, I could put the intranet hosts in different subnets.  It also
let me block any access through the router by any host that didn't match
on the MACs that were allowed in the router.  Most users don't change
the MAC address of their host, but some users will configure the OS to
report a different MAC address; i.e., the hardware (NIC) uses the same
manufacture-assigned MAC, but the OS sends a different MAC address.  Now
that I mentioned MAC addresses, and because the OS will cache the ones
it finds, maybe try clearing the arp cache, too:

arp -a

lists the arp cached MAC addresses, and their IP address at the time the
entries were cached.  ARP (Address Resolution Protocol) is used in
Windows, Mac, and Linux to connect to an intranet host on the same
network.  

To clear the ARP cache, run:

netsh interface ip delete arpcache

Think of ARP as an equivalent of the DNS client (local DNS caching) for
quickly finding hosts, but ARP is intranet versus DNS cache is mostly
for Intranet hosts.  Or think of ARP like a media control method of
quickly finding intranet hosts versus using the 'hosts' file.  I don't
know if you have multiple subnets, how traffic is controlled between
them, or not, dynamic IP addressing or static, etc.  Some more info on
ARP is here (and many other online articles):

https://www.simplehomelab.com/ways-to-clear-arp-cache/

As new network connections are established, the arp cache repopulates.
The above is a Windows/DOS command.  The ipconfig and netsh commands may
need to run inside a command shell with administrative priveleges.

You might want to visit the internal web server in the router to check
how it is configured to handle addressing and management of your
intranet hosts.

You said you cannot connect anywhere which means you also cannot connect
to the web server inside your router to configure its network management
functions, but only after booting into Ubuntu.  When booted into
Windows, and since you can get Internet connections, I'd start digging
into the config server settings in the router, or maybe just reset the
router to its default settings if you ever customized them away from the
defaults.