Network Services

Network Services

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