1. The most likely problem is that a rogue DHCP server has been introduced into the network and is handing this device an incorrect lease.

2. FTP uses both TCP ports 20 and 21 for the data channel and the control channel, respectively.

3. A DNS server uses TCP port 53 for zone transfers and UDP port 53 for name resolutions.

4. ICMP uses IP directly to build error-reporting packets that are transmitted back to the originating source host when issues arise during the delivery of data packets. ICMP is also used during ping and some Traceroute operations.

5. Quite simply, the service might not be running currently on that server. Another possibility might be that a firewall between the client and the server has blocked the protocol in question from passing.