title: why is "arp -a" showing inconsistent outputs that are vastly different?
body: <p>I have newly set up a computer with Ubuntu 18.04 and connected to my home wifi. When I try <code>arp -a</code> command to scan other devices connected to the same network, I see some very weird outputs.</p>
  <p>First, the connect is fine by checking <code>ifconfig</code>:</p>
  <pre><code>john@home:~$ ifconfig 
  lo: flags=73&lt;UP,LOOPBACK,RUNNING&gt;  mtu 65536
          inet 127.0.0.1  netmask 255.0.0.0
          inet6 ::1  prefixlen 128  scopeid 0x10&lt;host&gt;
          loop  txqueuelen 1000  (Local Loopback)
          RX packets 246054  bytes 21958490 (21.9 MB)
          RX errors 0  dropped 0  overruns 0  frame 0
          TX packets 246054  bytes 21958490 (21.9 MB)
          TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
  
  wlo1: flags=4163&lt;UP,BROADCAST,RUNNING,MULTICAST&gt;  mtu 1500
          inet 192.168.1.14  netmask 255.255.255.0  broadcast 192.168.1.255
          inet6 fe80::e3f:e0a5:2438:a96a  prefixlen 64  scopeid 0x20&lt;link&gt;
          inet6 240d:1a:6a5:c900:1420:b3cc:994b:1b7b  prefixlen 64  scopeid 0x0&lt;global&gt;
          inet6 240d:1a:6a5:c900:74f4:f504:3a41:bc12  prefixlen 64  scopeid 0x0&lt;global&gt;
          ether 04:33:c2:c4:02:a2  txqueuelen 1000  (Ethernet)
          RX packets 2452125  bytes 3302288691 (3.3 GB)
          RX errors 0  dropped 0  overruns 0  frame 0
          TX packets 964749  bytes 117659686 (117.6 MB)
          TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
  </code></pre>
  <p>It has the ip address of 192.168.1.14
  Then I tried <code>arp -a</code>:</p>
  <pre><code>john@home:~$ arp -a 
  ? (192.168.1.19) at 92:c4:78:3c:46:16 [ether] on wlo1
  _gateway (192.168.1.1) at e4:7e:66:1f:bf:4c [ether] on wlo1
  ? (192.168.1.5) at 26:36:46:f9:69:83 [ether] on wlo1
  </code></pre>
  <p>which makes sense because I can confirm that my ipad has ip address of <code>192.168.1.19</code> and my phone has ip address of <code>192.168.1.5</code></p>
  <p>However, after a while I executed <code>arp -a</code> again, and the output blows my mind:</p>
  <pre><code>john@home:~$ arp -a 
  ? (192.168.1.206) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.183) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.107) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.8) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.18) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.165) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.186) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.110) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.77) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.33) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.178) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.123) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.112) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.96) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.117) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.74) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.95) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.84) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.41) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.62) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.51) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.8) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.29) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.18) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.231) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.252) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.241) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.198) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.219) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.208) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.165) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.186) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.143) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.132) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.153) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.110) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.99) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.120) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.77) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.66) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.87) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.44) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.33) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.54) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.11) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.21) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.234) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.244) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.201) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.222) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.211) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.168) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.189) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.178) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.135) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.156) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.145) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.102) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.123) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.112) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.69) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.90) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.47) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.36) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.57) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.3) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.24) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.237) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.226) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.247) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.204) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.193) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.214) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.171) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.160) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.181) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.138) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.159) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.148) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.105) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.126) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.115) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.72) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.93) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.82) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.39) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.60) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.49) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.6) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.27) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.16) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.229) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.250) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.207) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.196) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.217) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.174) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.163) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.184) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.141) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.130) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.151) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.108) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.97) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.118) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.75) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.64) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.85) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.42) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.63) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.52) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.9) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.30) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.19) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.232) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.253) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.242) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.199) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.220) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.209) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.166) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.187) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.176) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.133) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.154) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.111) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.100) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.121) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.78) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.67) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.88) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.45) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.34) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.55) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.12) at &lt;incomplete&gt; on wlo1
  _gateway (192.168.1.1) at e4:7e:66:1f:bf:4c [ether] on wlo1
  ? (192.168.1.22) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.235) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.224) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.245) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.202) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.223) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.212) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.169) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.190) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.179) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.136) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.157) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.146) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.103) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.124) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.113) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.70) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.91) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.80) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.37) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.58) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.15) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.4) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.25) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.238) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.227) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.248) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.205) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.194) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.215) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.172) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.161) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.182) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.139) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.128) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.149) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.106) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.127) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.116) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.73) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.94) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.83) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.40) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.61) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.50) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.7) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.28) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.17) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.230) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.251) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.240) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.197) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.218) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.175) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.164) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.185) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.142) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.131) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.152) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.109) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.98) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.119) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.76) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.65) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.86) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.43) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.32) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.53) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.10) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.31) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.20) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.233) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.254) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.243) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.200) at &lt;incomplete&gt; on wlo1
  ? (192.168.1.221) at &lt;incomplete&gt; on wlo1
  john@home:~$ 
  </code></pre>
  <p>What is this?  What just happened?
  I thought <code>arp -a</code> is supposed to scan and list other devices on the same network. What are these results?</p>