Troubleshooting IPv4

You can use various commands to troubleshoot IPv4 to diagnose a problem; the most common ones are ifconfig , ping , and traceroute . These commands are each discussed briefly below.

ifconfig

Use the ifconfig -a command to view the current network interface configuration. The output from the command includes all physical and logical interfaces that are configured as shown here, where there are two logical interfaces:

 #ifconfig -a lo0: flags=1000849<UP,LOOPBACK,RUNNING,MULTICAST,IPv4> mtu 8232 index 1         inet 127.0.0.1 netmask ff000000 hme0: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2         inet 192.168.28.28 netmask ffffff00 broadcast 192.168.28.255         ether 8:0:20:b3:41:13 hme0:1: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2         inet 192.168.28.128 netmask ffffff00 broadcast 192.168.28.255 hme0:2: flags=1000843<UP,BROADCAST,RUNNING,MULTICAST,IPv4> mtu 1500 index 2         inet 192.168.28.29 netmask ffffff00 broadcast 192.168.28.255 

This output shows the status of each interface, in the flags= section. You can also verify that you are using the correct IPv4 address for each interface.

ping

Use the ping command to verify that you can contact the network interface and that it is responding to network requests . The following example contacts the logical interface hme0:2 :

 #ping 192.168.28.29 192.168.28.29 is alive 

traceroute

The traceroute command is extremely useful when you're trying to establish why you cannot contact a remote host; it identifies the path taken to reach a remote host. The following example traces the route, across the Internet, to the Web site www.example.com . It lists all the routers that are used to establish contact:

 #traceroute www.example.com Tracing route to www.example.com [192.0.34.166] over a maximum of 30 hops:   1     9 ms    10 ms     8 ms  10.25.0.1   2    11 ms     9 ms     9 ms  gsr01-st.blueyonder.co.uk [62.30.65.1]   3    13 ms    12 ms    14 ms  172.18.6.69   4    27 ms    14 ms    13 ms  tele1-azt-pos.telewest.net [194.117.136.2]   5    13 ms    12 ms    14 ms  pos50402hsd-gsr2-linx.cableinet.net [194.117.154.190]   6    14 ms    14 ms    12 ms  166.63.222.37   7   104 ms   103 ms   105 ms  dcr1-loopback.Washington.cw.net [206.24.226.99]   8   106 ms   105 ms   108 ms  bpr1-so-0-0-0.VirginiaEquinix.cw.net [208.173.52.113]   9   105 ms   105 ms   106 ms  bpr2-ae0.VirginiaEquinix.cw.net [208.173.50.253]  10   105 ms   106 ms   106 ms  208.173.50.146  11   137 ms   100 ms    95 ms  p16-1-0-0.r21.asbnva01.us.bb.verio.net [129.250.5.21]  12   108 ms   107 ms   106 ms  p16-5-0-0.r01.mclnva02.us.bb.verio.net [129.250.2.180]  13   108 ms   105 ms   108 ms  p16-7-0-0.r02.mclnva02.us.bb.verio. net [129.250.5.10]  14   166 ms   166 ms   184 ms  p16-0-1-2.r20.plalca01.us.bb.verio.net [129.250.2.192]  15   169 ms   168 ms   169 ms  p64-0-0-0.r20.snjsca04.us.bb.verio.net [129.250.2.71]  16   169 ms   167 ms   171 ms  xe-0-2-0.r21.snjsca04.us.bb.verio.net [129.250.2.73]  17   180 ms   214 ms   162 ms  p16-1-1-1.r21.lsanca01.us.bb.verio.net [129.250.2.186]  18   167 ms   182 ms   163 ms  ge-3-0-0.a02.lsanca02.us.ra.verio.net [129.250.29.131]  19   164 ms   166 ms   166 ms  ge-1-2.a01.lsanca02.us.ra.verio.net [129.250.46.93]  20   162 ms   165 ms   165 ms  ge-2-3-0.a02.lsanca02.us.ce.verio.net [198.172.117.163]  21   164 ms   164 ms   165 ms  lngw2-isi-1-pos.ln.net [130.152.80.29]  22   164 ms   164 ms   164 ms  207.151.118.18  23   165 ms   166 ms   165 ms  www.example.com [192.0.34.166] Trace complete. 

The output shows a successful trace of the route between two hosts . When there are problems, or there is no route, traceroute displays a * character instead.