Router Network Interface Resolution Encyclopedia

Editor's note: We will introduce and analyze the router network interface in this article through an example.

router# Show Interface e0/0
Ethernet0/0 is up, line protocol are down
Hardware is AmdP2, address is 0009.4375.5e20 (BIA 0009.4375.5e20)
Internet address is 192.168.1.53/24
MTU 1500 bytes, BW 10000 kbit, DLY 1000, USEC,
Reliability 172/255, Txload 3/255, Rxload 39/255
Encapsulation ARPA, loopback not set
Keepalive Set (SEC)
ARP Type:arpa, ARP Timeout 04:00:00
Last input never, output 00:00:07, output hang never
Last clearing of the "show interface" counters never
Input queue:0/75/0/0 (size/max/drops/flushes); Total output
drops:0
Queueing Strategy:fifo
Output Queue:0/40 (Size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets Input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 input packets with dribble condition detected
Packets output, 3270 bytes, 0 underruns
Output errors, 0 collisions, 2 interface resets
0 babbles, 0 late collision, 0 deferred
Lost Carrier, 0 no carrier
0 output buffer failures, 0 output buffers swapped out

(1) interface and active state

In the above display, the content indicates that the hardware interface is active, and the software process that handles the line protocol believes that the interface is available. If the router operator dismantles This hardware interface, the first field displays the information is administratively down. If the router receives more than 5,000 errors during the active interval, the word disabled appears in this field to show that the router automatically disables the port. The Row agreement field also displays one of the three descriptions previously mentioned: up, down, administratively down. If the field item is up, then the processing line protocol and the software process believe that this interface is available because she is receiving keepalives's purpose as well, Other devices can determine whether an idle connection is still active. For Ethernet interfaces, the default value for Keepalives is 10s. We will soon notice that the keepalives settings can be obtained by using the show Interfaces command for a specific interface. You can use the KeepAlive interface command to change the keepalives settings. The format of this command is as follows: Keepalive seconds

(2) Hardware field to provide you with the interface of the hardware type

In the example above, the hardware is the Cisco Extended Bus (Cxbus) Ethernet, the 533-mbps data bus for the interface processor. Therefore, the hardware informs us that the high-speed Cxbus interface processor is used to support Ethernet connections. Also note that the Display field includes the MAC address of the interface. The Mac is 48-bit long. Because the first 24 bits of the MAC address represent the manufacturer ID, the hexadecimal number 00-10-79 is the identifier assigned to Csico by the IEEE.

(3) Internet address

If an interface is configured for IP routing, it is assigned an Internet address. This address is followed by his subnet mask. The IP address is 205.141.192.1/24. The backslash (/) indicates that the first 24 digits of this address represent the network, and he is equal to the subnet mask 255.255.255.0.

(4) MTU

The Maximum Transmission Unit (MTU) represents the maximum number of bytes that are supported by the information field of the protocol running on the interface. Because the maximum length of the information field for an Ethernet frame is 1500 bytes, its MTU is displayed as 1500 bytes. For almost all Ethernet applications, the default 1500-byte MTU should be valid. For token rings, the default MTU value is 8192 bytes, but it should be noted that the MTU value recommended by RFC1191 is 17914 for the 16-mbps token Ring and 4464 bytes for the 4-mbps token ring. The minimum MTU is 64 bytes, and the maximum value is 65535 bytes. If the IP datagram exceeds the maximum MTU, it is segmented, which adds extra overhead because each final datagram contains its own header. While in a high-speed LAN connection, there is usually no need to worry about the extra cost associated with fragmentation, this can be a more serious problem on a Low-speed serial interface. You can change the default MTU by using the Mtuinterface command, which is formatted as follows:

MTU bytes

The number of bytes can be from 64~6553.

(5) BW

Interface bandwidth (BW) typically refers to the running rate of the interface, expressed in kilobytes per second. Because the Ethernet runs at a speed of 10Mbps, the BW value is shown as 000Kb.

The information bandwidth value can be set with the bandwidth command, but it is not actually used to adjust the bandwidth of the interface, because bandwidth is fixed for certain types of media, such as Ethernet. For other media, such as serial lines, it is usually adjusted to adjust the hardware to the speed of the operation. For example, you can increase or decrease the running speed of the serial interface by setting different clock rates on the DSU/CSU. Therefore, the main purpose of the bandwidth command is to communicate the current bandwidth to the high-level Protocol. You can set the bandwidth value in the following command format, thousands representing the bandwidth expressed in thousands per second. Bandwidth kilobits

(6) DLY

This field represents the delay of the interface, expressed in microseconds. Ethernet Latency (DLY) is 1000s. You can use the delay interface command to set a delay value for an interface. The format of this command is as follows:

Delay Tens-of-microseconds