what is the meaning of "link type is auto"? in the output of show int fa1/0

Answered Question
Jan 27th, 2009

Hi, all

I wonder the meaning of "link type is auto"

that was shown in the output of command

"show int fa1/0"

GGJU4F_SSW_S4507#2#sh int fastEthernet 4/25

FastEthernet4/25 is up, line protocol is up (connected)

Hardware is Fast Ethernet Port, address is 001e.f7d9.ede8 (bia 001e.f7d9.ede8)

Description: ## Vlan 920 ##

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

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Carrier delay is 0 msec

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

input flow-control is unsupported output flow-control is unsupported

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

Last input never, output never, output hang never

Last clearing of "show interface" counters 00:20:48

Input queue: 0/2000/0/0 (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

1158 packets input, 92184 bytes, 0 no buffer

Received 0 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 input packets with dribble condition detected

1928 packets output, 152207 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 output buffer failures, 0 output buffers swapped out

I have this problem too.
0 votes
Correct Answer by Elly Bornstein about 6 years 1 month ago

Sorry i thought it was mdix at first glance and the previous comments on this thread.

4503-1(config-if)#do show run int g1/1

Building configuration...

Current configuration : 141 bytes

!

interface GigabitEthernet1/1

speed nonegotiate

end

4503-1(config-if)#do show int g1/1 | i Mb

Full-duplex, 1000Mb/s, link type is force-up, media type is 1000BaseSX

It has to do with 'speed nonegotiate'. I believe it has to do with if you copper to fiber conversion. Meaning you have this command available on fiber GBIC ports so you can attempt to negotiate with a remote copper end if necessary. Honestly, I am not 100% sure, but this command is only there on fiber ports and it does change the link type from auto.

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Giuseppe Larosa Wed, 01/28/2009 - 01:22

Hello Sanghee,

the meaning is that the port has not been hard coded for a specific speed and duplex but it will try to negotiate with the NIC of the device connected to it both speed and duplex.

if instead you configure

int fas0/1

speed 100

duplex full

in sh int fas0/1 you should see

link type is 100 Full

Hope to help

Giuseppe

Sanghee Han Wed, 01/28/2009 - 16:53

Thanks for your reply.

as you saying, I checked the configuration.

but it has been configured with speed 100 and duplex full already.

Um....

device is cat4507 with IOS_12.2(25)EWA10.bin

would you give me more explanation?

pauloroque Wed, 01/28/2009 - 17:42

Hi hsh7603,

There are switches with more than one type of media for an interface. For exemple, a single interface can have two connector: a SPF (gbic) or rj-45. In such type of interface you may want to indicate using a command which one you will use. The configuration you choose is reflected in "link type".

int f0/24

media-type sfp

end

Sanghee Han Wed, 01/28/2009 - 18:36

Thanks for your reply.

but the switch supports just RJ45 type.

I attatch the show module.

GGJU4F_SG_S4507#1#sh mod

Chassis Type : WS-C4507R

Power consumed by backplane : 40 Watts

Mod Ports Card Type Model Serial No.

---+-----+--------------------------------------+------------------+-----------

1 2 Supervisor IV 1000BaseX (GBIC) WS-X4515 JAE1126NBSK

2 2 Supervisor IV 1000BaseX (GBIC) WS-X4515 JAE1132SYPC

3 48 10/100BaseTX (RJ45) WS-X4148-RJ JAE1123KAJ7

5 6 1000BaseX (GBIC) WS-X4306-GB JAE1129R244

7 48 10/100BaseTX (RJ45) WS-X4148-RJ JAE1142070E

as you recommend

I try it, but media-type command are unseen.

Of course it is right because it doen't support any media-type except RJ45.

In this case,

Link type is shown as auto?

Um....I don't know....

Elly Bornstein Wed, 01/28/2009 - 18:45

mdix is probably what it is.

it is used to detect rx from tx incase you ran out of xover cables

'no mdix auto'

fjcardenas-1 Thu, 01/29/2009 - 07:00

I have read that command "show int fa1/0" does not give a clue about speed or duplex being AUTO. So, I don't think that refers to speed or duplex settings.

Can that "link type auto" be related to auto-negotiate trunking?

Sanghee Han Thu, 01/29/2009 - 17:18

So do I.

I can't find the "no mdix auto" in configuration.

It doen't seen in both global and interface configuration level.

I am finding the relationship with trunking.

Anyone knows about this issue??

Correct Answer
Elly Bornstein Thu, 01/29/2009 - 17:50

Sorry i thought it was mdix at first glance and the previous comments on this thread.

4503-1(config-if)#do show run int g1/1

Building configuration...

Current configuration : 141 bytes

!

interface GigabitEthernet1/1

speed nonegotiate

end

4503-1(config-if)#do show int g1/1 | i Mb

Full-duplex, 1000Mb/s, link type is force-up, media type is 1000BaseSX

It has to do with 'speed nonegotiate'. I believe it has to do with if you copper to fiber conversion. Meaning you have this command available on fiber GBIC ports so you can attempt to negotiate with a remote copper end if necessary. Honestly, I am not 100% sure, but this command is only there on fiber ports and it does change the link type from auto.

Sanghee Han Thu, 01/29/2009 - 18:10

Thanks for your reply.

It is very helpful to me.

I think it seems to be not necessary for fastehternet because it does not force interface into nonegotiate.

although I change the speed and duplex into 100/full, but "show interface" shows link type is auto.

so link type in fast-ethernet will seem to be auto always.(I am not 100% sure ^^)

Thanks a lot.

Fernando Cannizzo Fri, 01/30/2009 - 05:06

Maybe you have the "negotiation auto" configured in the port.

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