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Displaying operational state of auto-MDIX?

I have a LAN of 3560's with several small consumer grade switches attached to them at various locations. All of the 3560 ports have auto-MDIX enabled. I am trying to determine if MDIX is actually in effect, i.e. if the port has the send & receive pairs flipped.

According to the 3560 command ref, the "show controller ethernet <interface name> phy" displays the operational status of auto-MDIX. That's great, but that command displays "Auto-MDIX: On" no matter what is connected to the port. In fact, it displays the same thing enven if NOTHING is connected to the port. For example:

Switch#sho int f0/2 status

Port Name Status Vlan Duplex Speed Type

Fa0/2 notconnect 11 auto auto 10/100BaseTX

Switch#sho cont eth f0/2 phy

FastEthernet0/2 (gpn: 4, port-number: 2)


0000: 3100 Control Register : 0011 0001 0000 0000

0001: 7809 Control STATUS : 0111 1000 0000 1001

0002: 0013 Phy ID 1 : 0000 0000 0001 0011

0003: 78FF Phy ID 2 : 0111 1000 1111 1111

0004: 03E1 Auto-Negotiation Advertisement : 0000 0011 1110 0001

0005: 0000 Auto-Negotiation Link Partner : 0000 0000 0000 0000

0006: 0004 Auto-Negotiation Expansion Reg : 0000 0000 0000 0100

0007: 2001 Next Page Transmit Register : 0010 0000 0000 0001

0008: 0000 Link Partner Next page Rx Regi : 0000 0000 0000 0000

0010: 01A4 Port Configuration Register : 0000 0001 1010 0100

0011: 0100 Port Status Register : 0000 0001 0000 0000

0012: A000 Interrupt Enable Register : 1010 0000 0000 0000

0013: 0000 Interrupt Status Register : 0000 0000 0000 0000

0014: 9990 LED Configuration Register : 1001 1001 1001 0000

001B: EB00 Trim Enable Register : 1110 1011 0000 0000

Auto-MDIX : On [AdminState=1 Flags=0x00052248]

00-20-7B, 0F-0F, 01-00


Am I missing something here? I also found the "show interface <interface name> transceiver properties" command, which also displays the MDIX administrative and operational status. However, this command also always shows the operational status as "On". The display for the same port as above:

Switch#show int f0/2 trans prop

Diagnostic Monitoring is not implemented.

Name : Fa0/2

Administrative Speed: auto

Administrative Duplex: auto

Administrative Auto-MDIX: on

Administrative Power Inline: N/A

Operational Speed: auto

Operational Duplex: auto

Operational Auto-MDIX: on

Media Type: 10/100BaseTX

Anyone know how to see if MDIX is actually in effect?

TIA - Jeff


Re: Displaying operational state of auto-MDIX?

Hi Jeff,

Look carefully at the command:

Auto-MDIX : On [AdminState=1 Flags=0x00052248]

ADMINSTATE=1 means Auto-MDIX is enabled

ADMINSTATE=0 means Auto-MDIX is disabled on the interface with:

int x/x

no mdix auto

"Auto-MDIX : On" means the switch is REALLY crossing the cable (to get a linkup)

"Auto-MDIX : Off" means the cable is not being crossed to get a linkup

See also my article on my blog:

Please rate.

New Member

Re: Displaying operational state of auto-MDIX?

Hi, thanks for responding.

As I said in the original post, the display Auto-MDIX: On does NOT mean that the cable is being crossed. The output of the command always displays that if auto-MDIX is administratively enabled. It displays that if another switch is connected to the port as you would expect it to. However, it also displays "auto-MDIX: On" if a normal host is connected to the port which is incorrect. It also displays that if NOTHING is connected to the port when it clearly is not flipping any pairs. I suspect that this is a bug in the code. I tried it with 12.2(25)SEE and 12.2(44)SE2 with the same results.


Re: Displaying operational state of auto-MDIX?


Have you hard-coded all interfaces with speed or duplex settings ?

If you do so, Auto MDIX gets disabled automatically and status flags would report all the same. If possible, post the interface configuration of the ports.

New Member

Re: Displaying operational state of auto-MDIX?

No, no hard-coded speed or duplex. Here is the original interface config:

interface FastEthernet0/31

switchport access vlan 2

switchport trunk encapsulation dot1q

switchport trunk native vlan 21

switchport trunk allowed vlan 2-4094

switchport mode access

auto qos voip cisco-phone

spanning-tree portfast


And then just for grins I set it to the default configuration and it made no difference.

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