Mac Geekery

I’m a tech support guy for a large ISP, and recently I came across a customer with a mac. He’s running ethernet directly to the cable modem. The mac is 10.4.9, and is recieving a valid IP. Modem is working nominally. I can ping the modem but no the mac. Firewall is turned off. Customer cannot ping out either, using DHCP, renewing produces the same IP. We sent one of our techs out there but I’m coming back to the problem, this is rare, most of the mac customers we have, never have this type of problem, soemthing happenign all the time with Windows customers. Where uninstalling the drivers and a reinstall resets tcp stack and settings etc. and they’re good to go. Is there an equivalent procedure with a Mac, Is creating a new location in network/ system preferences setting up a whole new stack for tcp or do all locations use the same one as my guess would be. Any help for future reference would be appreciated.