Cisco 3600 Series Multiservice Platforms

Duplicate MAC Addresses on Cisco 3600 Series

May 27, 1997

Problem Description

Cisco 3600 Series routers manufactured prior to May 23, 1997 have the potential for a Media Access Control (MAC) address conflict with other Cisco 3600 series routers. These routers were assigned four MAC addresses per slot when they were manufactured (for a total of eight MAC addresses for the 3620 and sixteen MAC addresses for the 3640). However, all versions of Cisco IOS assign sixteen MAC addresses per slot.

This can cause a MAC address conflict between a LAN network module in slot 1 of a 3600 and a LAN network module in slot 0 of the next 3600 router off the manufacturing production line. If two routers with the same MAC address are connected, the MAC address conflict will cause loss of connectivity.

If you do not have a MAC address conflict, these routers will operate normally in your network. You can check the MAC addresses of each interface with the show interface command, as shown below:

router#show interface ethernet 3/0
Ethernet3/0 is up, line protocol is up 
  Hardware is AmdP2, address is 0060.8338.3f21 (bia 0060.8338.3f21)

Problem Resolution

All Cisco 3600 series manufactured on May 23, 1997 and later are assigned sixteen MAC addresses per slot. If you have a MAC address conflict between 3600 routers in your network, you can resolve the conflict using one of the methods listed below:

  • Configure a new MAC address on one of the interfaces with the conflict. Use the interface configuration command mac-address to assign the new address, as shown below:

    router#configure terminal
    Enter configuration commands, one per line.  End with CNTL/Z.
    router(config)#interface ethernet 3/0
    router(config-if)#mac-address 0060.8322.2222
  • Exchange the 3600 router for another 3600 with a different base MAC address. The MAC addresses in 3600s are assigned to the motherboard, not to the individual network modules.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

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