Operation Manual

The output of ifconfig is split into the following sections:
• Link encap—The type of encapsulation used by the network, which on the Model B will either read Ethernet for the
physical network port or Local Loopback for the virtual loopback adaptor.
• Hwaddr—The Media Access Control (MAC) address of the network interface, written in hexadecimal. This is unique for
every device on the network, and each Pi has its own MAC address, which is set at the factory.
• inet addr—The internet protocol (IP) address of the network interface. This is how you find the Pi on the network if you’re
using it to run a network-accessible service, such as a web server or file server.
• Bcast—The broadcast address for the network to which the Pi is connected. Any traffic sent to this address will be
received by every device on the network.
• Mask—The network mask, which controls the maximum size of the network to which the Pi is connected. For most home
users, this will read 255.255.255.0.
• MTU—The maximum transmission unit size, which is how big a single packet of data can be before the system needs to
split it into multiple packets.
• RX—This section provides feedback on the received network traffic, including the number of errors and dropped packets
recorded. If you start to see errors appearing in this section, there’s something wrong with the network.
• TX—This provides the same information as the RX section, but for transmitted packets. Again, any errors recorded here
indicate a problem with the network.
• collisions—If two systems on the network try to talk at the same time, you get a collision which requires them to retransmit
their packets. Small numbers of collisions aren’t a problem, but a large number here indicates a network issue.
• txqueuelen—The length of the transmission queue, which will usually be set to 1000 and rarely needs changing.
• RX bytes, TX bytes—A summary of the amount of traffic the network interface has passed.
If you’re having problems with the network on the Pi, you should first try to disable and then re-enable the network interface.
The easiest way to do this is with two tools called ifup and ifdown.
If the network is up, but not working correctly—for example, if ifconfig doesn’t list anything in the inet addr section—start
by disabling the network port. From the terminal, type the following command:
sudo ifdown eth0
Once the network is disabled, make sure that the cable is inserted tightly at both ends, and that whatever network device the Pi
is connected to (hub, switch or router) is powered on and working. Then bring the interface back up again with the following
command:
sudo ifup eth0