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Muhammad Hassan

How to Set the Loopback to Specific Layer 3 Switch Interface

Please find the below show interface result of Layer 3 switch Port. Currently loopback not set to this interface. Please let me know how can i set the loopback to this particualr interface since loopback command not shown under this interface


sh int gigabitEthernet 0/23

GigabitEthernet0/23 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is a40c.c398.4541 (bia a40c.c398.4541)

Internet address is

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

reliability 255/255, txload 179/255, rxload 190/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:07:17, output 00:00:07, 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 74662000 bits/sec, 119491 packets/sec

5 minute output rate 70380000 bits/sec, 112017 packets/sec

287620166072 packets input, 22568453574431 bytes, 0 no buffer

Received 4601 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

274063186698 packets output, 21663572341938 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out


interface GigabitEthernet0/23

no switchport

ip address



SWITCH(config)#int gigabitEthernet 0/23



l2protocol-tunnel  lacp  link  load-interval  logging


Raju Sekharan
Cisco Employee

Hi Muhammad,

The loopback command is used on WAN interfaces.

It is not suported on normal ethernet interfaces. There are some ethernet SPA modules supporting it



Milan Rai

Dear Hassan,

Really you are confusing us could you configure loopback inside an Gig port.........

If you really want to configure loopback address then what about

SWITCH(config)#interface loopback 0

SWITCH(config-if)#ip add .............

If you mean to say anything else plz let me know....

And about the WAN interfaces (loopback address).......that is not supported on the l3 switch like c3560 Series.......

Thanks for your replies.

Actually, I saw loopback commad is supported on router ethernet interfaces. As you can see the above configuration we are using this partlicular port as layer 3 therfefore i expect it should support the same command on it.

Hi Hassan,

As I  mentioned earlier on some router modules it is supported

On which device are you trying this



Then, for what procedure do i need to follow in order to set this port as loopback.


Per my understanding, Ethernet OAM needs to be supported inorder to perform CFM or any loopback testing on ethernet ports. I remember working on 7600 platforms.

What platform and IOS version are you trying it?.



Ethernet Loopback is not supported on Switches.  You can use an external hard loop



Dear All,

I saw loopback command is shown under vlan interface but i need to set a particular Layer3 port.

SWITCH(config)#int vlan 1


link  load-interval  logging  loopback

Also, I need to perform remote loopback since there is no engineer at colo side to perform the hard loop.

Here are the IOS details:



Hassan Khan

I guess you may facing some P2P link issue with ISP, loopback on CKT always going to use by your ISP, what they do, they set soft loop or hard loop at your last mile ISP provided device after that you will get "loopback set" on sh interface command which is not showing currently

post that  you may try ping your own IP for checking purpose, this is troubleshooting process for checking error on CKT, please concern to your ISP and they will guide you accordingly.

I am looking for the same set of commands for a Cat 6500 switch

As I am no expert I was wondering if someone could explain to me what each type of loopback does

What I want is to run a test from the next hop component which in this case is a Genband MGW 4 port Gigabit Ethernet card to the Cisco 6500 switch and then back so that I can run a externalDataPath test on the Genband MediaGateway 15000 Passport.


+--+                   +-------+

| M |+-tx----rx-+|++    C   |

| G |                    |   |    6   |

| W |+-rx----tx-+|++   5    |

+--+                   |        0    |

                           |        0    |



Given my example above should I use

(config-if)# loopback


(config-if)# loopback internal


(config-if)# loopback mac


(config-if)# loopback driver


(config-if)# loopback external


Any help would be appreciated.



(config-if)# loopback