show interfaces
Displays detailed status and statistics for all interfaces or a specific interface, used to verify interface operational state, errors, and performance.
show interfacesWhen to Use This Command
- Troubleshooting a down interface by checking line protocol and status
- Monitoring interface errors like CRC, collisions, or input/output drops
- Verifying bandwidth, MTU, and duplex settings after configuration changes
- Checking interface counters to identify network congestion or hardware issues
Command Examples
Basic show interfaces output for a GigabitEthernet interface
show interfaces GigabitEthernet0/0GigabitEthernet0/0 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is 0011.2233.4455 (bia 0011.2233.4455)
Internet address is 192.168.1.1/24
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full Duplex, 1000Mbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
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
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 1000 bits/sec, 2 packets/sec
5 minute output rate 500 bits/sec, 1 packets/sec
1000 packets input, 500000 bytes, 0 no buffer
Received 1000 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
500 packets output, 250000 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped outLine 1: Interface status (up/down) and line protocol (up/down). 'up/up' means operational. Line 2: Hardware type and MAC address. Line 3: IP address and subnet mask. Line 4: MTU (1500 default), bandwidth (1 Gbps), delay, reliability (255/255 = 100%), load (1/255 = minimal). Line 5: Encapsulation (ARPA = Ethernet). Line 6: Keepalive interval. Line 7: Duplex and speed. Line 8: Flow control. Line 9: ARP type and timeout. Line 10: Last input/output activity. Line 11: Last time counters cleared. Line 12: Input queue stats (size/max/drops/flushes) and total output drops. Line 13: Queueing strategy. Line 14: Output queue size/max. Lines 15-16: 5-minute average input/output rates. Lines 17-18: Total packets/bytes input, broadcasts. Lines 19-20: Error counters: runts (<64 bytes), giants (>1518 bytes), throttles, input errors, CRC errors, frame errors, overruns, ignored. Lines 21-22: Watchdog, multicast, pause input, dribble condition. Lines 23-24: Output packets/bytes, underruns. Lines 25-26: Output errors, collisions, interface resets. Lines 27-28: Unknown protocol drops, babbles, late collisions, deferred. Lines 29-30: Lost carrier, no carrier, pause output. Lines 31-32: Output buffer failures, swapped out.
show interfaces with a specific interface that has errors
show interfaces FastEthernet0/1FastEthernet0/1 is up, line protocol is down
Hardware is Fast Ethernet, address is 0011.2233.4456 (bia 0011.2233.4456)
Internet address is 10.0.0.1/24
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 200/255, txload 50/255, rxload 75/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Half Duplex, 100Mbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:05, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 10/75/5/0 (size/max/drops/flushes); Total output drops: 3
Queueing strategy: fifo
Output queue: 5/40 (size/max)
5 minute input rate 5000000 bits/sec, 1000 packets/sec
5 minute output rate 3000000 bits/sec, 600 packets/sec
500000 packets input, 300000000 bytes, 10 no buffer
Received 5000 broadcasts (0 IP multicasts)
50 runts, 20 giants, 5 throttles
100 input errors, 30 CRC, 15 frame, 5 overrun, 10 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
400000 packets output, 200000000 bytes, 2 underruns
20 output errors, 15 collisions, 5 interface resets
10 unknown protocol drops
2 babbles, 3 late collision, 1 deferred
1 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped outLine 1: Interface is up but line protocol is down (likely no keepalive or layer 2 issue). Line 4: Reliability 200/255 (~78%) indicates errors. Loads are higher (txload 50/255 ~20%, rxload 75/255 ~30%). Line 7: Half Duplex (may cause collisions). Line 12: Input queue has drops (5). Line 15-16: High input/output rates. Line 18: 10 no buffer (packets dropped due to lack of buffer). Line 19: Runts (50), giants (20), throttles (5). Line 20: 100 input errors, 30 CRC (likely cabling issue), 15 frame errors, 5 overruns, 10 ignored. Line 24: 2 underruns (transmit side). Line 25: 20 output errors, 15 collisions (high for half duplex), 5 interface resets. Line 27: 3 late collisions (indicates duplex mismatch or cable length). Line 28: 1 lost carrier. These errors suggest duplex mismatch or faulty cable.
Understanding the Output
The 'show interfaces' command output is divided into several sections. The first line shows the interface status (up/down) and line protocol (up/down). 'up/up' means the interface is operational; 'up/down' indicates a layer 2 problem; 'down/down' means no cable or shutdown. The hardware and MAC address follow. The IP address is shown if configured. MTU, bandwidth (BW), delay (DLY), reliability (255/255 = 100%), and load (txload/rxload, 255/255 = 100%) indicate performance. Encapsulation is typically ARPA for Ethernet. Duplex and speed are critical: mismatches cause errors. The counters section shows input/output rates (5-minute average), total packets/bytes, and error counters. Key errors: runts (frames <64 bytes), giants (>1518 bytes), CRC (frame check sequence errors, often cabling), frame (alignment errors), overrun (input rate too fast), ignored (interface dropped packet), collisions (normal on half-duplex but high indicates duplex mismatch), late collisions (bad cable or duplex mismatch), interface resets (hardware issues). High input errors or CRC suggest physical layer problems. High output errors or collisions suggest duplex mismatch. Watch for 'no buffer' (packet drops due to memory) and 'input queue drops' (congestion). The output also shows queueing strategy and queue sizes. In a real network, use this command to baseline interface performance and troubleshoot connectivity or performance issues.
CCNA Exam Tips
CCNA exam tip: Remember that 'show interfaces' shows both status and line protocol; 'up/up' is fully operational, 'up/down' means layer 1 is up but layer 2 is down (e.g., no keepalive).
CCNA exam tip: Be able to identify duplex mismatch: look for late collisions and CRC errors on one side, and collisions on the other.
CCNA exam tip: The 'reliability' field is 255/255 for perfect; lower values indicate errors. The 'load' fields show interface utilization (255/255 = 100%).
CCNA exam tip: Know that 'show interfaces' counters are cumulative since last 'clear counters' command; exam may ask about resetting counters.
Common Mistakes
Mistake 1: Confusing 'status' and 'line protocol' — 'up/down' means cable is connected but no layer 2 keepalive or protocol mismatch.
Mistake 2: Ignoring CRC errors — they often indicate cabling issues or duplex mismatch, not just noise.
Mistake 3: Assuming 'collisions' are always bad — on half-duplex links, some collisions are normal; excessive collisions indicate a problem.
Related Commands
clear counters
Resets interface counters (e.g., input/output errors, packets) to zero, typically used to clear statistics before monitoring or troubleshooting.
show interfaces description
Displays a summary of all interfaces with their status, protocol, and description, useful for quickly verifying interface connectivity and administrative notes.
show interfaces status
Displays a summary of all switch interfaces including their status, VLAN, duplex, speed, and type, used to quickly verify interface connectivity and configuration.
Practice for the CCNA 200-301
Test your knowledge with hundreds of CCNA practice questions covering all exam domains.
Practice CCNA Questions