IOS Command "show mac-address-table address" also accepts formats like "00-12-34-56-78-90" and "00:12:34:56:78:90"

Both "00-12-34-56-78-90" and "00:12:34:56:78:90" formats work in IOS.


Without help of other automatic-discovery tools when finding out "which PC is attached to which switch port", I use "show mac-address-table address" command to locate that port. The last parameter to this command is MAC address of the PC in question.

I used to know the MAC address should be in "0012.3456.7890" format. However, I found that it could also be in formats such as "00-12-34-56-78-90" and "00:12:34:56:78:90"!

It would be much easier for us to do the cut-and-paste on the screen results of "ipconfig" or "ifconfig" on Windows and Unix hosts, respectively.



The following is a typical imaginary screen capture when I use this command to locate the switch port which the PC is connected to. Assume the PC's MAC address is "0012.3456.7890".

Switch>show mac-address-table address ?
  H.H.H  48 bit mac address

Switch>show mac-address-table address 0012.3456.7890
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
 225    0012.3456.7890    DYNAMIC     Fa0/2
Total Mac Addresses for this criterion: 1
Switch>

Then, I know this PC is attached to "FastEthernet0/2". (Assume this is not a trunk link and no other dumb switch/hub could be attached to this port.)

What is the problem? See the result of "ipconfig /all":

C:\Documents and Settings\User>ipconfig /all
.....

Ethernet adapter Local Area Connection:

        Connection-specific DNS Suffix  . :
        Description . . . . . . . . . . . : Broadcom NetXtreme Gigabit Ethernet
        Physical Address. . . . . . . . . : 00-12-34-56-78-90
        Dhcp Enabled. . . . . . . . . . . : No
        IP Address. . . . . . . . . . . . : 1.2.3.4
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
.....

Well, Windows uses the format of "00-12-34-56-78-90"! If IOS does not accept it, we have to manually replace "-" characters to none or ":", by our hand.

Luckily, IOS accepts it!

Switch>show mac-address-table address 00-12-34-56-78-90
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
 225    0012.3456.7890    DYNAMIC     Fa0/2
Total Mac Addresses for this criterion: 1
Switch>

Furthermore, IOS even accepts this format, which we often find on Unix hosts.

Switch>show mac-address-table address 00:12:34:56:78:90
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
 225    0012.3456.7890    DYNAMIC     Fa0/2
Total Mac Addresses for this criterion: 1
Switch>

Conclusion

Just cut-and-paste the MAC address screen output and search!