Making your own Cisco Router Managment Cable

The management cable is what allows you to change settings to your router over Hyperterminal. This is critical if your router is malfunctioning or you have disabled your Telnet access to protect from outside hacking and viruses. Once you're done with changing settings, you can unplug your management cable for extra protection from hackers. You don't need it attached for day-to-day use of your router.

If you've lost your management cable for your Cisco 675 or 678, you can make your own or get an electrically-inclined friend to make it for you.

Ingredients:

  1. 3 to 5 feet (or whatever length you want) of cable with at least three separate conductors.
  2. One DB9 female (socket) cable plug
  3. One RJ45 (ethernet sized) cable plug
  4. 3 short pieces of shrink tube of small diameter (for each individual conductor)
  5. 1 short piece of shrink tube of larger diameter (for all three conductors together)

Tools:

  1. Soldering iron & solder
  2. RJ45 crimping tool
  3. Wire cutters/strippers

If you have the right tools (i.e. an RJ45 crimper tool), you can buy a new DB9 female connector and an RJ45 connector and make a brand new nice cable according to the connection table below. You can get the plugs (and tools for that matter) from www.digikey.com if your local Radio Shack doesn't carry them.

If you don't have access to new cable plugs and an RJ45 crimping tool, you can hack together a couple of pre-made cables you might have lying around. All you really need are one serial cable with at least one socket end (DB9 female connector), and one ethernet cable end (type RJ45) with at least the centermost 4 pins connected to wires so you can reach them for splicing. Then the crude way would be to splice the individual wires of two prefab cables together according to the connection table below.

Management Cable, PC end Management Cable, Router End
DB9 Female Connector RJ45 Ethernet-type Connector
  • 1: No connection
  • 2: Connect to C
  • 3: Connect to D
  • 4: No connection
  • 5: Connect to E
  • 6: No Connection
  • 7: No connection
  • 8: No connection
  • 9: No connection
  • A: No connection
  • B: No connection
  • C: Connect to 2
  • D: Connect to 3
  • E: Connect to 5
  • F: No connection
  • G: No connection
  • H: No connection
Sorry for the quality of the diagrams. I drew them up quickly after analyzing my own Cisco-made management cable.

The numbering indicates which pins should be connected to which.