People use the Internet for a lot of different reasons. Its not
all client/server access. End-to-end communications occurs between
many applications. Its always interesting to watch what things
break when ISPs start filtering ports, even if it happens accidently.
A Comcast representative confirmed that the problem was with the cable
company. A routine upgrade of the software some Comcast routers use
inadvertently blocked access to certain server ports, the representative
said, adding that the problem was fixed late Monday. ISPs commonly use
port-blocking rules to restrict access to a server that may be generating
hacking attacks or other objectionable activity.