CCNA Course II

Transport Layer: two important agreements TCP and the UDP

Tcp:

• Connection-oriented protocol: to establish a connection (three handshake of TCP) before transmitting user data
• Error checking
• Packet serialization
• Reliability transfer: The data sent requires confirmation by the recipient, which is done through the serial number and confirmation number in the header.
• Data recovery capabilities

Udp

• No Connection Agreement
• provides limited error checking
• Provide the best possible transfer
• No data recovery capability

UDP header is simpler than TCP header word, less function, but high transmission efficiency

² three layers corresponding to four layers look at the Protocol field in the IP header 6 = TCP, + = UDP

² Layer Four corresponds to the application layer to see the port number in the TCP and UDP headers, different port numbers correspond to different applications

Common Port numbers:

	Tcp		Udp
Ftp	20,21	Ntp	123
Ssh	22	Snmp	161
Telnet	23	Rip	520
HTTP	80	Tftp	69
HTTPS	443	Dns	53
Smtp	25
POP3	110
Dns	53

Cisco device habits first match:

router>en

Router#conf T

Router (config) #no IP domain lo//Turn off domain lookup

Router (config) #hos R1//Setting the hostname of the device

R1 (config) #line Co 0//Enter the console line only one line behind the console can only be followed by 0

R1 (config-line) #logg S//close log synchronization to prevent system logs from interrupting user input

R1 (Config-line) #exec-T 0//Set automatic kick-out time under console line for permanent not kicking out

R1 (Config-line) #end

r1#

Turn on the virtual Terminal line (can telnet remotely):

r1>en

R1#conf T

R1 (config) #line vty 0 4//Open and enter the Vty line, 0 to 41 open 5 lines

R1 (config-line) #password 111//Set the password under the line to enter the password for remote Telnet

R1 (Config-line) #login//Enable remote login function

{The parentheses do not have to be fitted.}

R1 (config-line) #transport input Telnet//set protocol that can be logged in (default all)

R1 (config-line) #transport output telnet//device can log out of protocol (default all)

}

R1 (Config-line) #end

CDP: Cisco Discovery Protocol (CDP:CISCO Discovery Protocol) Cisco Discovery Protocol CDP is basically used to obtain the protocol address of neighboring devices as well as the platform to discover these devices.

r1>en

R1#conf T

R1 (config) #cdp the CDP protocol for Run//open device

R1 (config) CDP protocol #no CDP Run//shutdown device

R1 (config) #int f0/0

R1 (CONFIG-IF) #cdp the Enable//Open Interface CDP function

R1 (config-if) CDP function #no CDP enable//off interface

R1 (config-if) #end

The default global and interface are all CDP-enabled. If the global shutdown, the optical interface Open is not useful.

CCNA Course II