Strange LAN network problem - can't "see" just one address on LAN

[Bo Berglund]

On Sat, 12 Feb 2022 12:30:40 +0000, Chris Green <cl at isbd.net> wrote:

>On Sat, Feb 12, 2022 at 11:50:55AM +0000, Colin Law wrote:
>> On Sat, 12 Feb 2022 at 11:47, Chris Green <cl at isbd.net> wrote:
>> >
>> > Recently I have been trying out some changes to how the DHCP/DNS is
>> > managed and, for some strange reason, my desktop machine at
>> > 192.168.1.3 could no longer 'see' the router at 192.168.1.1.
>> 
>> Start by re-booting the router if you have not already done so.
>> Sometimes they get confused.
>> 
>Good advice, it was the router causing the problem though it wasn't
>that it needed a reboot.  
>
>I found that *any* system at 192.168.1.3 couldn't access the router at
>192.168.1.1.  This made diagnosis much easier because I could
>configure an unimportant system (as opposed to my mail/ssh server
>desktop) at 192.168.1.3 and try things.
>
>I searched through the router's settings (Draytek Vigor 2860n so there
>are a *lot* of settings) and I found a 'static route' I'd set while
>trying to get something else to work.  That static router referred to
>192.168.1.3 and was why I was getting my strange problem.  I've
>cleared the setting and all is well now.
>
>Phew! :-)

While you are at it you should *move away altogether* from the local LAN using
192.168.1.x or even worse 192.168.0.x addresses!
Better to use something like 192.168.179.x or similar, or even 10.231.156.x.

Why? You may ask...
Well since the IP range you are using is the default for many brands of routers
including hootels and the like, there are literally millions of LANs out there
with teh same addresses.
And you will have a hard time connecting back home using SSH (as you indicated)
or OpenVPN or similar because if your home LAN is on the same IP range as the
one you are connected to when calling in there is no way the call will be routed
through. It just disappears on the local LAN you currently use in the hotel or
similar....


-- 
Bo Berglund
Developer in Sweden