Weirdness on WiFi - new router

daniel.m.tripp · June 16, 2023, 12:55am

This is bizarre…

I couldn’t figure out what was going on when I tried to SSH from my Pop!_OS desktop machine to my Ubuntu 23.04 Thinkpad…

“Connection Refused”

Usually when something like that happens, I assume one of :

sshd is not running (or installed)
some kinda firewall is blocking access

Tested on the machine itself “ssh 0” and I get straight in (“0” being shorthand for “localhost”).
I can ssh to it from BOTH MacBooks… no drama! WTF? Stopped firewall (systemctl stop firewalld) - still no SSH access from Linux desktop to Linux laptop!

So - I enable WiFi on the desktop machine, and I’m straight in… Weird!

I’m sure this wasn’t happening BEFORE I got a new router, and/or new PCIe wifi card for the Thinkpad… Hmmm…

This warrants further investigation - I don’t think it’s the new WiFi CHIP on the Thinkpad, it’s either something on my router that won’t allow all comms / bridged across WiFi and ethernet, or, some wonky Ubuntu thing…

Note: Synergy works perfectly (server is on ethernet, Thinkpad client is on WiFi). Also had a session (ssh from desktop to laptop) open, and it stayed alive when I disabled WiFi on the desktop, so I exited, and reconnected (i.e. ethernet only) and I got straight in… Bizarro!

Never seen this happen before… Perplexing…

Hmmm - just thought - it might be some arp cache type thing, i.e. changed MAC address (when I replaced the PCIe card on the Thinkpad)?

Weird alright! I can’t even ping my personal MacBook from my Linux desktop…

I’m going to reboot EVERYTHING and see if it’s dodgy arp tables or something!

All that effort for zero reward (rebooting stuff) - still happened - then “LIGHT BULB MOMENT” :

That Thinkpad had a dedicated lease on my old router, i.e. fixed IP address via DHCP - and I’d “conveniently” plonked an entry into /etc/hosts on my Linux box…

Which is closely related to the symptom “if something’s not working, check DNS first!” issue…

pdecker · June 16, 2023, 1:45am

That’s what I do for the few things I want a “static” IP. Most things I don’t care what the IP is. I’ve never had a problem communicating whether it was “static” or dynamic, but in my case they’re all assigned via DHCP.

daniel.m.tripp · June 16, 2023, 4:20am

I keep most of my server thingies in the first 100 IP addresses, and limit the router to 100-199… But even so - I do occasionally set fixed DHCP leases outside of that “scope” and it works… e.g. my NAS, TVHeadEnd Pi3, Transmission-Daemon OPi 2E+… And then I have other servers at 200+…

Unrelated, but I saw a great gig the other night, UK’s “The Sleaford Mods” on their tour downunder for their 2023 album “UK Grimm” - and the “musician” dude, Andrew Fearns, plays samples on a ThinkPad running Windows XP - he just sets the track, then bops like a raver, while vocalist Jason Williamson does the words, live : but anyway - Mr Fearn’s has stickers all over his ThinkPad, so I thought I’d do the same with mine - these are mix of metal music (but also an Aussie rapper Seth Sentry) and Geek stuff - most of the Geek stickers were from “UNIX Stickers” packs (except for the SGI logo) :

The album playing in Sayonara is DEVILLE from Sweden’s 2022 album “Heavy Lies The Crown” (stoner / doom hard/heavy rock) - and I’m catching them with my headbanger Kiwi mate tomorrow week (a stoner / doom “festival” with other bands called “Spliffs n Riffs Pt 2” - I went to Pt1 in March).