I have a simple three node wireless linux network as follows:

hostname IP notes
crs 192.168.0.101 laptop
cuda-host 192.168.0.100 desktop
192.168.0.103 wireless router ethernetted to WIFI modem

/etc/hosts on crs and cuda-host look like:
--->
127.0.0.1 localhost
127.0.1.1 crs -or- cuda-host
192.168.0.101 crs
192.168.0.100 cuda-host
<---
From crs I can ping (and ssh) cuda-host but from cuda-host I can't ping (or ssh) crs. Instead I get:
--->
craig@cuda-host:~$ ping crs
PING crs (192.168.0.101) 56(84) bytes of data.
From cuda-host (192.168.0.100) icmp_seq=1 Destination Host Unreachable
From cuda-host (192.168.0.100) icmp_seq=2 Destination Host Unreachable
From cuda-host (192.168.0.100) icmp_seq=3 Destination Host Unreachable
<----
doing arp-scan from cuda-host I don't see crs. What I get is:
---->
craig@cuda-host:~$ sudo arp-scan -I wlan0 -l
Interface: wlan0, datalink type: EN10MB (Ethernet)
Starting arp-scan 1.8.1 with 256 hosts (http://www.nta-monitor.com/tools/arp-scan/)
192.168.0.1 1c:af:f7:cc:85:cb D-LINK INTERNATIONAL PTE LIMITED
192.168.0.103 50:63:13:c1:7d:f5 Hon Hai Precision Ind. Co.,Ltd.

2 packets received by filter, 0 packets dropped by kernel
Ending arp-scan 1.8.1: 256 hosts scanned in 1.781 seconds (143.74 hosts/sec). 2 responded
<-----
D-LINK is my wireless modem. I thought .103 was my wireless modem. have never heard of the company Hon Hai. Arp-scan looks similar on crs

Any idea what's going on here?

Thanks,

Craig

I don't like that.
It's good to have the 192.168.x network in /etc/hosts (Uf the IPs are static) but I would not list a box by it's ip and 127.0.0.1. Hosts is for other boxes.

There are 3 boxes, so three lines in /etc/hosts
127.0.0.1 line
router line
other box line (crs on cuda-host; cuda-host on crs)

Ping is a two way test. It proved what you wanted to know in the first test. That being a connection. The things that could stop it are the ability to offer or accept icmp. That could include the host, client or any device in between or firewalls or ports.