Ubuntu – Ubuntu Server 18.04 Destination Host Unreachable

ping gateway from both computers ping 192.168.1.254 then try to ping comp1 to compt2 and comp2 to comp1 then post results of arp -a from BOTH boxes

Edit

Interesting, something is blocking traffic

run sudo tcpdump -ni wlan0 arp in one window on both computers and then try pinging each other and the gateway from another window on both again and post results

Edit2

So far that shows that comp1 is doing what it's suppose to sending arp request (asking for comp2s etherner address) but not getting an arp reply (hearing anything back). Need to see the tcpdump from PC2 to see the full picture. Either run the screen command or do this on PC1 sudo tcpdump -w pc1.pcap -ni wlan0 arp & and on PC2 sudo tcpdump -w pc2.pcap -ni wlan0 arp & & should throw it in the background and give you your prompt back for pings. After pings fail bring the jobs back to foreground with fg %1 stop it ctrl+c and read the written files with sudo tcpdump -r pc1/2.pcap

Edit3 PCs are doing what they're suppose to, putting ARPs out but they're not getting through which points to the router. Maybe a disable firewall setting, doubt it supports VLANs? Kinda wish you let it run a bit longer at 22:45:48.379058 your router sent its own ARP request when it was looking for PC1 22:45:48.379058 ARP, Request who-has 192.168.1.77 tell 192.168.1.254, length 28 both PCs should've seen it, we can see that PC1 saw it and replied with its IP but cant tell if PC2 got it since since you stopped it stop just short at 22:45:09.796214. Assuming you're clocks are synced with NTP that is.

Edit4

See that it's still not resolved. Didn't see that you have eth adapters on both PCs. Can you hardwire into the router on eth instead of wlan and see if you can ping then? Or get another router? Or make a hotspot on the phone connect both PCs and try to ping? Also, surprised to see that you were able to connect two PCs together and ping each other did you use a crossover cable?

You shouldn't have messed with the pre-existing lo (loopback) interface: you need to revert that to

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

and then add your external static interface, for example

auto em1
iface em1 inet static
address 192.168.1.120
netmask 255.255.255.0
network 192.168.1.0
gateway 192.168.1.1

(these are not necessarily correct for your network: you will need to verify). You will also likely need to add at least one DNS nameserver e.g. to use Google's public DNS servers

dns-nameservers 8.8.8.8  8.8.4.4

Alternatively, if your router supports DHCP address reservation you might want to use that instead - it's arguably simpler, especially for home networks.