Basic Network Troubleshooting
Networking issues can be problematic when working on a remote server. If you accidentally break your Cloud Server’s networking capabilities, you may find yourself locked out of any remote connection. However, many networking problems can be solved by logging into the web console (through your The Rackspace Cloud Control Panel) and running a few simple commands.
ip addr show
ip addr show is a basic network information and configuration tool. On a working Cloud Server, its output may look something like this:
# ip addr show eth0 Link encap:Ethernet HWaddr 40:40:d9:xx:xx:xx inet addr:67.23.13.xx Bcast:184.108.40.206 Mask:255.255.255.0 inet6 addr: fe80::4240:d9ff:fe05:xxxx/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:36564 errors:0 dropped:0 overruns:0 frame:0 TX packets:11490 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:48350683 (46.1 MiB) TX bytes:1456436 (1.3 MiB) eth1 Link encap:Ethernet HWaddr 40:40:a5:xx:xx:xx inet addr:10.176.44.xx Bcast:10.176.63.255 Mask:255.255.224.0 inet6 addr: fe80::4240:a5ff:fe5f:xxxx/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:3 errors:0 dropped:0 overruns:0 frame:0 TX packets:53 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:230 (230.0 B) TX bytes:7764 (7.5 KiB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
If, upon running ifconfig, you do not see an IP address under eth0, try
ip addr show eth0 220.127.116.11 netmask 255.255.255.0 up
where “18.104.22.168” is the static IP for your Cloud Server as given to you when the server was created. If you do not see an eth0 interface at all, run
This will bring up the interface under its default configuration. Similar steps may be followed to fix the internal connection by using ‘eth1’ and your assigned private (10.xx.xx.xx) IP.
iptables is a commonly-used firewall in Linux. By default, your Cloud Server should have iptables already installed, but it will not be configured. To list the firewall rules, run
A newly-built server will show the following:
# iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination
If your iptables output differs from the above, the firewall may be causing your issue.
route is used to view and edit the routing table. The output of route may display several lines, but the most important (or the most commonly broken) is one called the default gateway.
Note: Various Linux distros may configure their routes slightly differently. The output shown below is from a Debian server.
# route Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 22.214.171.124 * 255.255.255.0 U 0 0 0 eth0 10.176.32.0 * 255.255.224.0 U 0 0 0 eth1 10.191.192.0 10.176.32.1 255.255.192.0 UG 0 0 0 eth1 10.176.0.0 10.176.32.1 255.248.0.0 UG 0 0 0 eth1 default 126.96.36.199 0.0.0.0 UG 0 0 0 eth0
In this example, the first line is a “catch-all” for the 67.23.13.xx network, while the next three lines are specific to the internal network. The last line is the default gateway, and should point to xx.xx.xx.1 (where the first three octets match those of the top line).
To change the default route, run
route add default gw xx.xx.xx.1
replacing “xx.xx.xx” as described above.
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