There are two general types of network services, which are connection less and connection oriented.Connection oriented service performs connection establishment, data transfer, and connectiontermination.
Ping
The "ping" program uses ICMP echo message requests and listens for ICMP echo message replymessages from its intended host. Using the -R option with ping enables the record route feature. If thisoption is used ping will set the record route (RR) in the outgoing ICMP IP datagram
Traceroute
The "traceroute" program uses ICMP messaging and the time to live (TTL) field in the IP header. Itworks by sending a packet to the intended host with a TTL value of 1. The first router will send back theICMP "time exceeded" message to the sending host. Then the traceroute program will send a messagewith a TTL of 2, then 3, etc. This way it will get information about each router using the informationreceived in the ICMP packets. To get information about the receiving host, the message is sent to a portthat is not likely to be serviced by that host. A ICMP "port unreachable" error message is generated andsent back.
Telnet
Some telnet command codes and their meanings
Command Code Description
- 236 - EOF
- 237 - SUSP - Suspend the current process
- 238 - ABORT - Abort process
- 239 - EOR - End of record
- 240 - SE - Suboption end
- 241 - NOP - No operation
- 242 - DM - Data Mark
- 243 - BRK - Break
- 244 - IP - Interrupt process
- 245 - AO - Abort output
- 246 - AYT - Are you there
- 247 - EC - Escape character
- 248 - EL - Erase Line
- 249 - GA - Go ahead
- 250 - SB - Suboption begin
- 251 - WILL - Sender wants to enable option / Receiver says OK
- 252 - WONT - Sender wants to disable option / Receiver says not OK
- 253 - DO - Sender wants receiver to enable option / Receiver says OK
- 254 - DONT - Sender wants receiver to disable option / Receiver says not OK
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