Interface show Commands

The router keeps track of lots of information about its interfaces: the number of packets sent, the number of errors, addresses, and so on. You can get most of this information by using one of the show commands.

5.10.1. Clearing the show Command Counters

Much of the information the router tracks is numeric, such as running counts of the number of packets that went out the interface. These counters aren't particularly meaningful unless you know when the counter started counting. To clear the counters that are displayed in the show interface commands, use the clear counters command. This command does not clear the values that are retrieved from SNMP commands, but only the values reported by the show commands discussed in this section. Here are some typical clear counters commands:

Router#clear counters ethernet0
Router#clear counters serial0
Router#clear counters

The first two commands clear the counters for a specific interface; the last command clears the counters for all the interfaces.

All counters are unsigned long integers, which means they can go up to about 4 billion before they roll over to 0 (232 - 1).

 

5.10.2. Listing All Interfaces

If you don't know what physical interfaces are available on your router, use the show version command. You'll find a list of interfaces at the end of its output. Here's what happens on a Cisco 2524:

Router>show version
...
cisco 2524 (68030) processor (revision J) with 6144K/2048K bytes of memory.
Processor board ID 08291960, with hardware revision 00000000
Bridging software.
X.25 software, Version 2.0, NET2, BFE and GOSIP compliant.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
FT1 CSU/DSU for Serial Interface 0
No module installed for Serial Interface 1
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read ONLY)

This router has one Ethernet port, two serial ports, and one built-in CSU/DSU installed on serial interface 0.

5.10.3. Using the show interface Commands

The show interface command displays protocol-specific statistics for the interface. All interfaces report both generic information and media-specific information. For example, here's what you get if you ask for information about an Ethernet segment:

Router>show interface ethernet0
Ethernet0 is up, line protocol is up
 Hardware is Lance, address is 0010.7b39.e28e (bia 0010.7b39.e28e)
 Description: Office Ethernet segment
 Internet address is 10.10.1.1/29
 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255
 Encapsulation ARPA, loopback not set, keepalive set (10 sec)
 ARP type: ARPA, ARP Timeout 04:00:00
 Last input 00:00:00, output 00:00:00, output hang never
 Last clearing of "show interface" counters never
 Queueing strategy: fifo
 Output queue 0/40, 0 drops; input queue 0/75, 0 drops
 5 minute input rate 2000 bits/sec, 3 packets/sec
 5 minute output rate 17000 bits/sec, 3 packets/sec
 11938498 packets input, 4102863937 bytes, 0 no buffer
 Received 60515 broadcasts, 0 runts, 0 giants, 0 throttles
 8 input errors, 0 CRC, 0 frame, 0 overrun, 8 ignored, 0 abort
 0 input packets with dribble condition detected
 12556989 packets output, 1981671402 bytes, 0 underruns
 0 output errors, 11702 collisions, 1 interface resets
 0 babbles, 0 late collision, 20150 deferred
 0 lost carrier, 0 no carrier
 0 output buffer failures, 0 output buffers swapped out

Table 5-4 shows how to interpret this information.

Table 5-4. Information from a show interface command

Field	Meaning
Up/down	Whether the interface is up and configured. If the interface is administratively down, the shutdown command has been applied to this interface. If the interface is down, it is not receiving any signal from the attached network cable.
Line protocol	Whether the encapsulation protocol is up or down for this interface. If your interface is up but the line protocol is down, check the encapsulation or see if the line has been unplugged.
Hardware	The type of interface (serial, Ethernet, etc.).
Internet address	The IP address and subnet mask for this interface.
MTU	The Maximum Transmission Unit for this interface (the maximum frame/packet size).
BW	The bit rate in kbps (default is 1544 for serial, 10000 for Ethernet). This value is actually the setting from the interface's bandwidth command, which is used in route metric calculations but has no other impact on the router. In particular, this value has nothing to do with the actual speed at which data is transferred.
DLY	The expected delay for a packet traversing this interface. Like the bandwidth, this parameter is used only for IGRP/EIGRP route metric calculations. Its value can be set with the delay interface command.
rely	The reliability of this link, as a number between 1 and 255. The value 255/255 indicates that the link is 100% reliable.
load	The traffic load on the segment, as a number between 1 and 255. The value 255/255 indicates that the link is at 100% of capacity. 1/255 is the lowest value.
Encapsulation	The encapsulation type for this link. For serial links, the encapsulation might be PPP or HDLC. For Ethernet, it might be ARPA.
loopback	Whether the interface is in the loopback state. If you cannot send packets across your link, you may have loopback set.
keepalive	Whether keepalives are active on this link.
ARP Type	Type of Address Resolution Protocol
Last input/last output	How long it has been since a packet was received or sent on this interface. This field is not an actual time value, but the number of hours, minutes, and seconds since the packet was received or sent. If the time exceeds 24 hours, the field overflows and asterisks are printed.
output hang	The time since this interface was last reset because of a transmission that took too long to complete. If the time exceeds 24 hours, the field overflows and asterisks are printed.
Last clearing of "show interface" counters	The time since a clear counters command has been run on this interface. (In other words, the time since counters were reset.)
Queueing strategy	The type of queuing that is enabled on this interface: First In First Out (FIFO), Weighted Fair Queuing (WFQ), Priority, Custom, and so on.
Output queue/input queue	The number of packets in both the input and output queues. The number is in the format "number in queue/max size of queue, number of drops."
5 minute	The five-minute average input and output rate. The rate is given in both bits per second and packets per second over the last five minutes.
packets input	Number of successful error-free packets this interface has received.
bytes input	Number of successful error-free bytes this interface has received.
broadcasts	Number of multicast or broadcast packets this interface has received.
runts	Number of packets this interface threw away because they were smaller than the minimum packet size.
giants	Number of packets this interface threw away because they were larger than the maximum packet size. Can be caused by a bad NIC card somewhere on the network.
throttles	Number of times the receiver on the port was disabled. This can occur because of buffer or processor overload.
input error	Total number of errors encountered by this interface. These errors can include runts, giants, CRC errors, overruns, ignored packets, aborts, buffer overflows, and frame errors.
CRC	The number of checksum failures encountered by this interface. A checksum failure occurs when the calculated checksum does not match the checksum sent by the sending device. Lots of CRC errors mixed with a low number of collisions on an Ethernet interface is an indicator of excessive noise, which points to cable issues.
frame	The number of frame errors encountered by this interface. These occur when a packet that is malformed or does not contain the correct number of bytes is delivered to the interface. Can be caused by cabling or duplex mismatch.
overrun	The number of overrun errors within this interface. This occurs when the low-level device driver fails to read a byte before the serialization hardware completes receiving the next byte.
ignored	The number of packets ignored by this interface. This occurs when the internal buffers are full and the interface ignores incoming packets because it has no place to store them. Can be caused by broadcast storms.
abort	The number of aborts on this interface. Occurs because of a timing problem between the router and serial device.
dribble condition detected	This counter increments every time a frame is too long. The frame is still accepted by the router.
packets output	The total number of packets this interface has transmitted.
bytes output	The total number of bytes this interface has transmitted.
underruns	The number of underrun errors on this interface. Occurs when the low-level device driver fails to provide the next byte to be serialized before the previous one has been completely transmitted. Can be caused by a device transmitting to the interface faster than it can handle.
output errors	The number of errors that occurred when this interface tried to transmit.
collisions	The number of times two hosts sent a packet at the same time; a small number is normal.
interface resets	The total number of times this interface reset due to errors.
babbles	The number of times that the Transmit Jabber Timer expired. A jabber is a frame that is longer than 1518 octets, but does not end with an even number of octets.
late collisions	The number of times a collision is detected late in the packet transmission process. This number should always be 0 on a properly configured network. If you see these, suspect a duplex setting or a hardware problem.
deferred	The number of frames that have been transmitted successfully after they had been waiting because the media was busy. Most often seen in half-duplex environments.
lost carrier	Number of times the interface lost carrier during a transmission. If you are seeing these on your interface, suspect a bad cable. (Check both sides of the connection.)
no carrier	Number of times no carrier was present on the interface. As in lost carrier, suspect a bad cable (on both sides) if you see these.
output buffer failures/ output buffers swapped out	The number of failed buffers and the number of buffers swapped out. These counters can be a normal sign of an overworked segment. It might mean that the buffers filled up and packets were dropped. If the segment isn't all that busy, look at the speed/duplex settings and see if they match the amount of traffic this interface is handling.

 

5.10.3.1. show interface accounting

Another interesting show command is show interface interfacename accounting. This command gives you a quick overview of the interfaces and their packet counts:

Firewall#show interface ethernet0 accounting
Ethernet0
 Protocol Pkts In Chars In Pkts Out Chars Out
 IP 10659150 62307981 13906422 3947809402
 ARP 272756 17240212 126066 7563960
 CDP 76294 23585301 186904 57192624

This command displays the accounting statistics for the ethernet0 interface. It shows the packets received (Pkts In), characters received (Chars In), packets transmitted (Pkts Out), and characters transmitted (Chars Out) for each protocol. On this router, the protocols in use are IP, ARP (Address Resolution Protocol), and CDP (Cisco Discovery Protocol).

5.10.3.2. show ip interface

The show ip interface command gives you detailed information about an interface's IP configuration. The related command show ip interface brief provides a summary of the IP configuration for all the router's interfaces. Here's the result of show ip interface ethernet0:

Router#show ip interface ethernet0
Ethernet0 is up, line protocol is up
 Internet address is 10.200.212.1/24
 Broadcast address is 255.255.255.255
 Address determined by non-volatile memory
 MTU is 1500 bytes
 Helper address is not set
 Directed broadcast forwarding is disabled
 Multicast reserved groups joined: 224.0.0.10
 Outgoing access list is not set
 Inbound access list is 145
 Proxy ARP is enabled
 Security level is default
 Split horizon is enabled
 ICMP redirects are always sent
 ICMP unreachables are always sent
 ICMP mask replies are never sent
 IP fast switching is disabled
 IP fast switching on the same interface is disabled
 IP multicast fast switching is disabled
 Router Discovery is disabled
 IP output packet accounting is disabled
 IP access violation accounting is disabled
 TCP/IP header compression is disabled
 Probe proxy name replies are disabled
 Gateway Discovery is disabled
 Policy routing is disabled
 Network address translation is disabled

Table 5-5 explains each line in the output.

Table 5-5. Explanation of show ip interface output

Output	Explanation
Internet address is 10.200.212.1/24.	Gives the IP address and subnet mask that are currently set for the interface. For this interface, the network mask is /24, which is equivalent to 255.255.255.0.
Broadcast address is 255.255.255.255.	Gives the broadcast address for this interface. The default is 255.255.255.255; it can be modified with the ip broadcast-address command.
Address determined by non-volatile memory.	Specifies the source from which the IP address for the interface was retrieved.
MTU is 1500 bytes.	Specifies the Maximum Transmission Unit for this interface. This can be modified with the ip mtu command.
Helper address is not set.	The ip helper-address command sets a destination address for UDP broadcasts. In this example, it is not set. It is normally used to forward BOOTP or other UDP services to a server.
Directed broadcast forwarding is disabled.	Specifies whether directed broadcasts are enabled. Directed broadcasts are normally disabled, but can be enabled using the ip directed broadcasts command. See the description of directed broadcasts earlier in this chapter.
Multicast reserved groups joined.	Lists the multicast group joined by this interface.
Outgoing access list is not set.	Shows the outgoing access list for the interface. The ip access-group number out command sets the access list.
Inbound access list is 145.	Shows the incoming access list for the interface. The ip access-group number in command sets the access list.
Proxy ARP is enabled.	Gives the status of proxy ARP, either enabled or disabled. See the ip proxy-arp description earlier in this chapter.
Security level is default.	Gives the IPSO security level for this interface.
Split horizon is enabled.	Gives the status of split horizon on this interface, either enabled or disabled. Use the command ip split-horizon to enable it. This topic is covered in Chapter 8.
ICMP redirects are always sent.	Shows the status of ICMP redirects, either allowed or not. The ip redirects command enables them.
ICMP unreachables are always sent.	Specifies whether ICMP unreachable messages are sent from this interface. The ip unreachables command enables this feature.
ICMP mask replies are never sent .	Specifies whether ICMP mask replies are sent. The ip mask-reply command enables this feature.
IP fast switching is disabled.	Specifies whether the fast-switching cache for outgoing packets is enabled. Use ip route-cache to enable it.
IP fast switching on the same interface is disabled.	Specifies whether the fast-switching cache for packets on the same interface is enabled. Use ip route-cache to enable it.
IP multicast fast switching is disabled.	Specifies whether the fast-switching cache for outgoing multicast packets is enabled. Use ip mroute-cache same-interface to enable it.
Router Discovery is disabled.	Specifies whether router discovery is enabled. Use the ip irdp command to enable it.
IP output packet accounting is disabled.	Specifies whether IP output packet accounting is enabled. If enabled, this line will also describe the accounting threshold. Use the ip accounting command to enable it.
IP access violation accounting is disabled.	Specifies whether access violation accounting is enabled. Use the ip accounting access-violations command to enable it.
TCP/IP header compression is disabled.	Specifies whether TCP header compression is enabled. Use the ip tcp header-compression command to enable it.
Probe proxy name replies are disabled.	Specifies whether the IP probe proxy is enabled. Use the ip probe proxy command to enable it.
Gateway Discovery is disabled.	Specifies whether gateway discovery is enabled. Use the ip gdp command to enable it.
Policy routing is disabled.	Specifies whether policy routing is enabled. The ip policy command enables it.
Network address translation is disabled.	Specifies whether NAT is enabled on this interface. The ip nat command enables address translation. However, it requires some extensive configuration. For more information, see Chapter 13.

Here's the output from show ip interface brief . The output is fairly straightforward, except for the meaning of the Method column. This column is the same as the Address determined by non-volatile memory field in Table 5-5.

Router#show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0 10.200.212.1 YES NVRAM up up
Ethernet1 10.200.210.30 YES NVRAM up up
Serial0 unassigned YES unset administratively down down
Serial1 unassigned YES unset administratively down down