Invalid MAC Address for SiS 900-Based NIC

I replaced a router performing Network Address Translation (NAT) at a site with a Cisco Pix 501 firewall. Once I had the Pix firewall configured, all of the other systems on the LAN were able to ping the firewall and access the Internet. However, the Windows Small Business Server (SBS) 2003 domain controller was not able to access the Internet nor even ping the firewall. Yet it could ping all the Windows XP systems on the LAN and the Solaris 10 server on the LAN. It was plugged into one of the ports on the firewall and could ping the other systems connected to the firewall, just not the firewall itself. Nor could I successfully ping the domain controller from the firewall.

Checking the configuration of the server, with ipconfig /all, I saw that its MAC address, i.e. the physical address, was all zeroes.

C:\Documents and Settings\Administrator>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : crystal
Primary Dns Suffix  . . . . . . . : example.com
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : example.com

Ethernet adapter Server Local Area Connection:

Connection-specific DNS Suffix  . :
Description . . . . . . . . . . . : SiS 900-Based PCI Fast Ethernet Adapter
Physical Address. . . . . . . . . : 00-00-00-00-00-00
DHCP Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 192.168.1.7
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1
DNS Servers . . . . . . . . . . . : 192.168.1.7
			            217.68.70.72
Primary WINS Server . . . . . . . : 192.168.1.7

When I monitored the network traffic between the firewall and server using Microsoft's Network Monitor, I could see ARP requests from the firewall and replies from the domain controller. Yet, when I checked the ARP table on the firewall with the show arp command, I did not see the domain controller's MAC address. The arp -a command on the domain controller did show the firewall's MAC address in its ARP cache, however.

I suspected the Pix firewall was not accepting a MAC address of all zeros. When I tried to manually enter the MAC address on the Pix firewall with the arp command, it declared the address to be invalid.

The ipconfig /all command showed the network adapter in the domain controller as a "SiS 900-Based PCI Fast Ethernet Adapter". Peforming a Google search on whether others had encountered a MAC address of all zeros with this adapter, I found that using the default driver Windows XP provides for this adapter yields an all-zero MAC address for the adapter. The same appears to be true for SBS 2003 systems. Responses to a posting at Anyone else with ideas for SIS 900 ethernet?1 , indicated that updating the driver for the network adapter might resolve the problem. This is apparently a common problem with motherboards that have this network adapter built-in^{2, 3}. I thought updating the driver might require a reboot. I didn't want to reboot the server, so I changed its MAC address, instead, to a valid MAC address, which resolved the problem. Once I did that, I could ping the firewall from the server and vice versa and access the Internet. The change did not require a reboot.

The steps to modify the MAC address are as follows:

Click Start.
Click on Connect To.
Select Show all connections.
Right-click on Server Local Area Connection and select Properties.
Click on Configure
Click on the Advanced button.

SiS 900-based NIC before MAC
change

Click on Network Address and select Value.
Put in an arbitrary network address (don't use any ":" or "-" between digits, just enter 12 hexadecimal digits, but not all "F's", that don't match any other MAC address on the LAN.

Note: putting in an arbitrary MAC address will confuse any utilities that check MAC addresses of all systems on a LAN and try to determine the model and manufacturer of the
NIC from MAC addresses, since specific ranges are assigned to network adapter manufacturer's, but otherwise it shouldn't matter what MAC address you use. I used 000CF1C89910 in this case. At linksys wusb v.2.6 - using on WinXP⁴, I saw the following address listed for the same adapter:
```
Description . . . . . . . . . . . : SiS 900-Based PCI Fast ethernet adapter
Physical Address. . . . . . . . . : 00-E0-18-82-79-A4
```
You could use that same address, since presumably it is a valid one for that adapter or just change the last digit.
Click on OK. You can then go to a command prompt and verify that Windows is now reporting a new non-zero MAC address with the ipconfig /all command. After I made the change, I saw the information below:
```
   Description . . . . . . . . . . . : SiS 900-Based PCI Fast Ethernet Adapter
   Physical Address. . . . . . . . . : 00-0C-F1-C8-99-10
```

I was then able to ping the firewall and access the Internet from the domain controller. Though I encountered the problem with a Pix firewall, it is likely other firewalls, routers, or switches might also reject an all-zero physical, aka MAC or Ethernet, address as well.

References: