[PLUG] Local network routing mystery

[David Fleck]

My wife and I have 2 practically identical ThinkPad laptops, both running OpenSUSE 42.3.  They connect to a wireless router via DHCP.  We also have several desktop machines (Linux & FreeBSD) with static IP addresses. All the machines are connected by a router.  Both laptops can see the router, the outside world, and each other.  But one laptop can see all the desktops, and the other one can't see any of them. The desktops can't see the one laptop, either.

As far as I can see, the routing tables are the same on both laptops:
m2:~ #  route  ### This is the non-connecting laptop
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.1.1     0.0.0.0         UG    600    0        0 wlan0
192.168.1.0     *               255.255.255.0   U     600    0        0 wlan0

dcf:~> route   ### This is the connecting laptop
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.1.1     0.0.0.0         UG    600    0        0 wlan0
192.168.1.0     *               255.255.255.0   U     600    0        0 wlan0

But when I try to ping from the non-connecting laptop:
m2:~ # ping 192.168.1.9
PING 192.168.1.9 (192.168.1.9) 56(84) bytes of data.
^C
--- 192.168.1.9 ping statistics ---
5 packets transmitted, 0 received, 100% packet loss, time 3999ms

whereas:
dcf:~> ping 192.168.1.9
PING 192.168.1.9 (192.168.1.9) 56(84) bytes of data.
64 bytes from 192.168.1.9: icmp_seq=1 ttl=64 time=9.59 ms
64 bytes from 192.168.1.9: icmp_seq=2 ttl=64 time=0.960 ms
64 bytes from 192.168.1.9: icmp_seq=3 ttl=64 time=0.960 ms

I'm flummoxed. Everything I can think to look at on the non-connecting laptop looks right, but the machines simply don't 'see' each other, even though they can see other machines on the network and there is no difference in network topology distinguishing connecting and non-connecting machines. Reboots (of desktops and the laptop) haven't helped.

Last data point: this was all working correctly 24 hours ago.

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- David Fleck