linux ifconfig command output explained

8/1/2014 Linux ifconfig Command Output Explained

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Linux ifconfig Command Output

Following is a typical output that we get on executing the ifconfig command.

# ifconfig

eth0 Link encap:Ethernet HWaddr 00:0C:29:40:93:9C

inet addr:192.168.154.102 Bcast:192.168.154.255 Mask:255.255.255.0

UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

RX packets:1771 errors:0 dropped:0 overruns:0 frame:0

TX packets:359 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:138184 (134.9 KiB) TX bytes:49108 (47.9 KiB)

Interrupt:67 Base address:0x2000

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





The left margin displays the name of the interface which are eth0 and lo interfaces in our case. Lets have

a closure look at the output of eth0 interface.

Link encap:Ethernet HWaddr 00:0C:29:40:93:9C

Link Encap

This represents the frame type associated with this interface.

In this case, it is ethernet.

HWaddr

This represents the hardware address of the ethernet interface.

Hardware address is also commonly known as MAC address.

MAC address consists of 6 octets (48 bits) and is divided in two parts. First three octets (00:0C:29)

represents the manufacturer id and the last three octets (40:93:9C) represents the serial number

assigned to the device by the manufacturer.

MAC adddress is a global unique identifier for a network interface.



inet addr:192.168.154.102 Bcast:192.168.154.255 Mask:255.255.255.0

inet addr

IPv4 address assigned to the interface.

Bcast

Broadcast address of the network associated with the interface.

Mask

Network mask associated with the interface.

UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

UP

This flag indicates that the network interface is configured to be enabled.

BROADCAST

Indicates that the interface is configured to handle broadcast packets.

This is important for obtaining the IP address via DHCP server.

RUNNING

Indicates that the network interface is operational and is ready to accept the data.

MULTICAST

Indicates that the interface is configured to handle multicast packets.

MTU

The maximum transmission unit for which the interface is configured.

MTU is a link layer charcteristic which provides limit on the size of the Ethernet frame. If IP has a

datagram to send and the size of the datagram is larger than the link layers MTU then IP layer breaks

the datagram into smaller pieces (fragments), so that each is smaller than the MTU.

1500 is the default value for all ethernet devices.

Metric 1

Interface metric is used to compute the cost of a route. It tells the OS which interface a packet should be

forwarded to, when multiple interfaces could be used to reach the packets destination.


RX Packets



The number of packets received via the interface.

RX errors

The number of damaged packets received.

RX dropped

The number of dropped packets due to reception errors.

RX overruns

The number of received packets that experienced data overruns.

RX frame

The number received packets that experienced frame errors.


TX Packets

The number of packets transmitted via the interface.

TX errors

The number of packets that experienced transmission error.

TX dropped

The number of dropped transmitted packets due to transmission errors.

TX overruns

The number of transmitted packets that experienced data overruns.

TX carriers

The number received packets that experienced loss of carriers.


TX collisions

The number of transmitted packets that experienced Ethernet collisions. A nonzero value of this field

indicates possibility of network congestion.

txqueuelen

The field provides the information about the configured length of transmission queue.




RX bytes

The total bytes received over this interface.

TX bytes

The total bytes transmitted over this interface.

Interrupt:67 Base address:0x2000

Interrupt

This field provides the information about the Interface Request (IRQ) value assigned to this interface.

Base address

The I/O base address associated with this interface.

linux ifconfig command output explained

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