Couple of thoughts...
It's not really clear to me what piece of gear on your network is acting as your router/physical connection to the Comcast network.
Instead of entering the ip's for the Comcast DNS servers in MacTCP, have you considered just giving MacTCP a single DNS server address, being that of your router? This assumes that your router can be configured for DNS caching. I believe you would then have to enter the router address in both the gateway and ip address fields in the MacTCP client.
Do you have other utilities outside of MacTCP to do a traceroute from the Classic box to confirm it can get to the outside world by ip even if DNS is not working for you?
It would be a pain in the butt, but you could try a hosts file... if you hard wire a couple of outside websites with ip addresses and you can reach them, then you are probably right, you have a DNS issue.
But, perhaps it is actually a NAT issue. Kind of a WAG, but maybe your router doesn't know how to NAT MacTCP, or vice versa?
Here's a link to a page with some MacTCP info from Adam Engsts Internet Starter Kit. It has some info about the hosts, DNR and prep files which might be helpful. Plus some suggestions for MacTCP utilities.
http://emperor.tidbits.com/Personal/Adam/books/iskm/iskm3html/pt4/ch17/ch17.html#aa10
It's not really clear to me what piece of gear on your network is acting as your router/physical connection to the Comcast network.
Instead of entering the ip's for the Comcast DNS servers in MacTCP, have you considered just giving MacTCP a single DNS server address, being that of your router? This assumes that your router can be configured for DNS caching. I believe you would then have to enter the router address in both the gateway and ip address fields in the MacTCP client.
Do you have other utilities outside of MacTCP to do a traceroute from the Classic box to confirm it can get to the outside world by ip even if DNS is not working for you?
It would be a pain in the butt, but you could try a hosts file... if you hard wire a couple of outside websites with ip addresses and you can reach them, then you are probably right, you have a DNS issue.
But, perhaps it is actually a NAT issue. Kind of a WAG, but maybe your router doesn't know how to NAT MacTCP, or vice versa?
Here's a link to a page with some MacTCP info from Adam Engsts Internet Starter Kit. It has some info about the hosts, DNR and prep files which might be helpful. Plus some suggestions for MacTCP utilities.
http://emperor.tidbits.com/Personal/Adam/books/iskm/iskm3html/pt4/ch17/ch17.html#aa10