Networking Services and Ports

There are two general types of network services, which are connection less and connection oriented. Connection oriented service performs connection establishment, data transfer, and connection termination.

Ping

The “ping” program uses ICMP echo message requests and listens for ICMP echo message reply messages from its intended host. Using the -R option with ping enables the record route feature. If this option 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. It works by sending a packet to the intended host with a TTL value of 1. The first router will send back the ICMP “time exceeded” message to the sending host. Then the traceroute program will send a message with a TTL of 2, then 3, etc. This way it will get information about each router using the information received in the ICMP packets. To get information about the receiving host, the message is sent to a port that is not likely to be serviced by that host. A ICMP “port unreachable” error message is generated and sent 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

On items 251 through 254 above, a third byte specifies options as follows:

ID        Name                          RFC

1          Echo                            857

3          Supress go ahead        858

5          Status                          859

6          Timing Mark              860

24        Terminal type                         1091

31        Window size               1073

32        Terminal speed           1079

33        Remote flow control 1372

34        Line mode                   1184

36        Environment variables 1408