Can't access another Ubuntu on WAN. ssh,ping,tracepath,nmap all fail. How to fix?

My ubuntu system is connected to wireless network and I can access internet. I can ping 8.8.8.8 or google.com but I can't ping another Ubuntu system on the same wireless network. I tried ping, ssh, nmap, tracepath all failed. Please suggest what I can do to resolve this issue.

rob@yasu:~$ nmap -sn 10.0.0.0/24

Starting Nmap 7.01 ( https://nmap.org ) at 2016-05-07 12:21 EDT

Nmap scan report for 10.0.0.1

Host is up (0.0010s latency).

Nmap scan report for 10.0.0.9

Host is up (0.000033s latency).

Nmap done: 256 IP addresses (2 hosts up) scanned in 15.40 seconds

rob@yasu:~$ tracepath 10.0.0.9

1: 10.0.0.9 0.123ms reached

 Resume: pmtu 65535 hops 1 back 1 

rob@yasu:~$ tracepath 10.0.0.1

1?: [LOCALHOST] pmtu 1500

1: 10.0.0.1 1.440ms reached

1: 10.0.0.1 5.162ms reached

 Resume: pmtu 1500 hops 1 back 1 

rob@yasu:~$ tracepath 10.0.0.4

1?: [LOCALHOST] pmtu 1500

1: 10.0.0.9 785.561ms !H

1: 10.0.0.9 2890.676ms !H

 Resume: pmtu 1500 

rob@yasu:~$ ping 10.0.0.1

PING 10.0.0.1 (10.0.0.1) 56(84) bytes of data.

64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=4.28 ms

64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=1.12 ms

^C

--- 10.0.0.1 ping statistics ---

2 packets transmitted, 2 received, 0% packet loss, time 999ms

rtt min/avg/max/mdev = 1.121/2.704/4.287/1.583 ms

rob@yasu:~$ ping 10.0.0.9

PING 10.0.0.9 (10.0.0.9) 56(84) bytes of data.

64 bytes from 10.0.0.9: icmp_seq=1 ttl=64 time=0.038 ms

64 bytes from 10.0.0.9: icmp_seq=2 ttl=64 time=0.066 ms

^C

--- 10.0.0.9 ping statistics ---

2 packets transmitted, 2 received, 0% packet loss, time 999ms

rtt min/avg/max/mdev = 0.038/0.052/0.066/0.014 ms

rob@yasu:~$ ping 10.0.0.4

PING 10.0.0.4 (10.0.0.4) 56(84) bytes of data.

From 10.0.0.9 icmp_seq=1 Destination Host Unreachable

From 10.0.0.9 icmp_seq=2 Destination Host Unreachable

^C

--- 10.0.0.4 ping statistics ---

3 packets transmitted, 0 received, +2 errors, 100% packet loss, time 1999ms

pipe 2