Changing the Default MAC Address

Each attachment to an FDDI network is identified by a unique 48-bit MAC address. By default, the first SunFDDI card takes the host-resident MAC address, which is stored in nonvolatile memory (NVRAM) on the motherboard of the machine. Each subsequent SunFDDI card adopts the card-resident MAC address stored in its own IDPROM.

In general, this convention is sufficient to ensure that each SunFDDI card installed in the machine has a unique MAC address. However, there may be a conflict with other LAN interfaces that also take the host-resident MAC address--for example, an Ethernet (le) interface or a SunFDDI 2.0 (bf) interface. In this event, change the default MAC address assigned to the first SunFDDI card installed in the system.

To Change the Default MAC Address with pf_macid or nf_macid

Use the pf_macid(1M) or the nf_macid(1M) utility to recover the card-resident MAC address, and then modify the system files to override the default MAC address:

1. Become superuser.

2. Use the pf_macid(1M)or nf_macid(1M)utility to recover the MAC address from the IDPROM on the SunFDDI interface identified by the instance number <inst>.

   ---

   # <basedir>/nf_macid nf<inst>
   <mac_address>
   

   ---

3. Modify the start-up file on your machine so that the MAC address is assigned correctly when the system is rebooted.

   1. Edit the /etc/rcS.d/S30rootusr.sh file to add the following if statement immediately after the ifconfig command that initializes the interface nf<inst>.

      If you are changing the MAC address of more than one interface, add one if statement for each interface.

      ---

      ifconfig $1 plumb
      	if [ $1 = "nf<inst>" ]; then
      			ifconfig nf<inst> ether <mac_address>
      	fi
      

      ---

      On most systems, the /etc/rcS.d/S30rootusr.sh file is a hard link to the /etc/rootusr file.

4. Reboot your machine to assign the new MAC address to the SunFDDI interface.

When a SunFDDI card takes the host-resident MAC address, it can be swapped to another system without affecting the existing network. However, once a station starts sending packets on the network, the Address Resolution Protocol (ARP) updates the ARP tables on other stations to include the MAC address of its interface. The ES-IS protocol performs the same function for SunFDDI OSI running over FDDI. If you swap SunFDDI cards that use the card-resident MAC address, you must wait until the ARP entries time-out, or remove the ARP entries from every active station manually before packets can be routed correctly.