The Boston Diaries

The ongoing saga of a programmer who doesn't live in Boston, nor does he even like Boston, but yet named his weblog/journal “The Boston Diaries.”

Go figure.

Friday, February 15, 2002

“I've got those cable MAC blues … ”

I finally got the firewall from Condo Conner moved to the Facility in the Middle of Nowhere, and just as I had feared, our cable connection wasn't passing traffic to it since the network card in the firewall had a different MAC address.

I know that it is possible to change the MAC address on a NIC but not having done it before I had to do some research. I found out that under Unix, it's easily done with one command:

ifconfig interface hw ether MAC address

Spring and I had to leave to meet some friends, but I gave the information to Rob for him to play around with it. The idea was to change the MAC address on the firewall interface to match the NIC in Rob's machine, and then change the MAC address on Rob's machine, or swap out the NIC.

Upon returning home, Rob had some success with it. He was able to set the MAC address on the firewall to match his computer and get traffic through, but with a 60% packet loss. Looking into the problem it turned out to be that the cable modem was set for 100Base-T while the NIC in the firewall is a 10Base-T interface. The fix for that was to power cycle the cable modem and allow it to sync at 10Mbs instead of 100Mbs.

But Rob didn't want to play around with changing MAC addresses—he wanted to get the cable modem to use the firewall's MAC address. He had attempted to call the cable provider but the technician he got did not understand what Rob wanted. We'll be using his box for the gateway for the time being.

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