11-18-2008 01:48 PM - edited 03-06-2019 02:33 AM
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
Switch#
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
11-19-2008 12:40 AM
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:
http://mayafarm.no-ip.com/?p=23
Please rate.
11-19-2008 06:51 AM
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.
11-19-2008 11:58 AM
Hi,
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.
11-19-2008 12:48 PM
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
end
And then just for grins I set it to the default configuration and it made no difference.
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