我有 3 台设备。在一个网络上，一台设备可以看到另一台设备，但它们都看不到第三台设备。它们位于同一个 wi-fi ad-hoc 网络中。其中2人相见，1人无人相见。设备距离很近（10 厘米）。如何找出原因？
对于一个不和别人一起玩的人：
这是 ifconfig：
root@edison:~# ifconfig wlan0
wlan0 Link encap:Ethernet HWaddr 78:4b:87:a9:87:53
inet addr:192.168.2.50 Bcast:192.168.2.255 Mask:255.255.255.0
inet6 addr: fe80::7a4b:87ff:fea9:8753/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1528 Metric:1
RX packets:1342297 errors:0 dropped:852312 overruns:0 frame:0
TX packets:158162 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:80024954 (76.3 MiB) TX bytes:10973582 (10.4 MiB)
这是 iwconfig：
root@edison:~# iwconfig wlan0
wlan0 IEEE 802.11abgn ESSID:"pi-ad-hoc"
Mode:Ad-Hoc Frequency:2.427 GHz Cell: 3A:41:3D:F5:20:A2
Tx-Power=31 dBm
Retry long limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:on
这是 iwlist 扫描（奇怪的是它显示多个网络同名）：
Cell 01 - Address: 3A:41:3D:F5:20:A2
Channel:4
Frequency:2.427 GHz (Channel 4)
Quality=70/70 Signal level=-4 dBm
Encryption key:off
ESSID:"pi-ad-hoc"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Ad-Hoc
Extra:tsf=0000002153a8a359
Extra: Last beacon: 90ms ago
IE: Unknown: 000970692D61642D686F63
IE: Unknown: 010882848B962430486C
IE: Unknown: 030104
...
Cell 06 - Address: 2E:5D:62:E8:17:46
Channel:4
Frequency:2.427 GHz (Channel 4)
Quality=70/70 Signal level=0 dBm
Encryption key:off
ESSID:"pi-ad-hoc"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Ad-Hoc
Extra:tsf=00000021521e98ce
Extra: Last beacon: 25920ms ago
IE: Unknown: 000970692D61642D686F63
IE: Unknown: 010882848B962430486C
IE: Unknown: 030104
...
Cell 08 - Address: 0A:27:49:3D:49:E9
Channel:4
Frequency:2.427 GHz (Channel 4)
Quality=70/70 Signal level=0 dBm
Encryption key:off
ESSID:"pi-ad-hoc"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Ad-Hoc
Extra:tsf=0000002153313756
Extra: Last beacon: 7920ms ago
IE: Unknown: 000970692D61642D686F63
IE: Unknown: 010882848B962430486C
IE: Unknown: 030104
...
Cell 09 - Address: E2:32:E6:6A:CC:A9
Channel:4
Frequency:2.427 GHz (Channel 4)
Quality=70/70 Signal level=0 dBm
Encryption key:off
ESSID:"pi-ad-hoc"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Ad-Hoc
Extra:tsf=0000002153a96297
Extra: Last beacon: 40ms ago
IE: Unknown: 000970692D61642D686F63
这是 ping：
root@edison:~# ping 192.168.2.2
PING 192.168.2.2 (192.168.2.2): 56 data bytes
^C
--- 192.168.2.2 ping statistics ---
8 packets transmitted, 0 packets received, 100% packet loss
root@edison:~# ping 192.168.2.1
PING 192.168.2.1 (192.168.2.1): 56 data bytes
^C
--- 192.168.2.1 ping statistics ---
7 packets transmitted, 0 packets received, 100% packet loss
root@edison:~#
这里是其中之一确实有效：
平：
pi@pi3-2:~ $ ping 192.168.2.1
PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.
64 bytes from 192.168.2.1: icmp_seq=1 ttl=64 time=8.13 ms
64 bytes from 192.168.2.1: icmp_seq=2 ttl=64 time=6.99 ms
64 bytes from 192.168.2.1: icmp_seq=3 ttl=64 time=7.80 ms
64 bytes from 192.168.2.1: icmp_seq=4 ttl=64 time=7.39 ms
^C
--- 192.168.2.1 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 6.998/7.584/8.138/0.441 ms
pi@pi3-2:~ $ ping 192.168.2.50
PING 192.168.2.50 (192.168.2.50) 56(84) bytes of data.
^C
--- 192.168.2.50 ping statistics ---
9 packets transmitted, 0 received, 100% packet loss, time 7999ms
如果配置：
pi@pi3-2:~ $ ifconfig wlan0
wlan0 Link encap:Ethernet HWaddr b8:27:eb:67:07:fc
inet addr:192.168.2.2 Bcast:192.168.2.255 Mask:255.255.255.0
inet6 addr: fe80::ac7f:b393:aac1:78bf/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1528 Metric:1
RX packets:1287637 errors:0 dropped:158601 overruns:0 frame:0
TX packets:487835 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:91775299 (87.5 MiB) TX bytes:46478896 (44.3 MiB)
配置文件
pi@pi3-2:~ $ iwconfig
wlan0 IEEE 802.11bgn ESSID:"pi-ad-hoc"
Mode:Ad-Hoc Frequency:2.427 GHz Cell: 3A:41:3D:F5:20:A2
Tx-Power=31 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:on
iwlist wlan0 扫描
pi@pi3-2:~ $ iwlist wlan0 scan
wlan0 Scan completed :
Cell 01 - Address: 3A:41:3D:F5:20:A2
Channel:4
Frequency:2.427 GHz (Channel 4)
Quality=70/70 Signal level=-35 dBm
Encryption key:off
ESSID:"pi-ad-hoc"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s
9 Mb/s; 12 Mb/s; 18 Mb/s
Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Ad-Hoc
Extra:tsf=0000000000000000
Extra: Last beacon: 154751220ms ago
IE: Unknown: 000970692D61642D686F63
IE: Unknown: 010882848B960C121824
IE: Unknown: 030104
IE: Unknown: 06020000
IE: Unknown: 32043048606C
IE: Unknown: DD070050F202000100
IE: Unknown: 010882848B962430486C
IE: Unknown: 2A0100
IE: Unknown: 32040C121860
IE: Unknown: 2D1A21001FFF00000000000000000000000000000000000000000000
IE: Unknown: 3D1604001300000000000000000000000000000000000000
IE: Unknown: DD09001018020010000000