Guia Ccna

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Cisco™ CCNA : OSI and TCP/IP
OSI MODEL
Application : Responsible for identifying and establishing the availability of desired
comm partner and verifying sufficient resources exist for comm. Ex: FTP, SMTP
TCP/IP MODEL

Presentation : Responsible for presenting the data in standard formats. Some
Presentation layer standards are JPEG, MPEG, MIDI, PICT, Quick Time, TIFF.Session : Responsible for co-ordinating communication between systems/nodes.
Some of the session layer protocols and interfaces: NFS, RPC, SQL, ASP, DNA SCP

Application : Defines TCP/IP application protocols and how
host programs interface with transport layer services to use
the network. Ex: FTP, SMTP, Telnet

Transport : Provides communication session management between
host computers. Ex:TCP, UDP

Transport : Responsible for multiplexing upper-layer applications, session mgmt
tearing down of virtual circuits, flow control and to maintain data integrity.

Network : Responsible for sending packets from the source network to the destination
network using routing methods. Routers work at network layer.

Datalink : Consists of LLC sublayer and MAC sublayer. LLC handles errorcontrol, flow
flow control, framing etc. MAC handles access to shared media such as ethernet.

Internet : Performs routing of IP datagrams.

Ex: IP, ARP, ICMP

Physical : Controls the hardware devices and media that make
up the network.

Physical : Responsible for ultimate transmission of data over network communications
media. Some of the standard interfaces at physical layer areEIA/TIA-232, V.24,V.35, HSSI

Port numbers used by TCP/UDP

Some important port numbers
FTP : Port 20-21
TFTP : Port 69

Telnet : Port 23
SMTP : Port 25

DHCP : Ports 67 and 68
DNS : Port 53

POP3 : Port 110
HTTP : Port 80

0-255 : Used for public applications
255-1023 : Assigned to companies
Above 1023 : Used by upper layers to set up sessions with other hosts and by
TCP to use assource and destination addresses.

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Cisco™ CCNA : IOS
Internal memory components of a cisco router

Router Cursor Commands

ROM : Memorycontaining micro-code for basic functions to start and maintain the router.
RAM/DRAM : Stores the running configuration, routing tables, and packet buffers.
NVRAM : Memory that does not lose information when power is lost. Stores the system’s
configuration file and the configuration register.
Flash Memory : Stores the compressed IOS image.

A: Move to the beginning of the command line
E:Move to the end of the command line
F: Move forward one character, same as using “Right Arrow”
B: Move backward one character, same as using “Left Arrow".
P: Repeat Previous command, same as using “Up Arrow”
N: Repeat Next (more recent) command, same as using "Down Arrow"
B: Moves to beginning of previous word.
F: Moves to beginning of next word.
R: Creates new command prompt,followed by all the
characters typed at the last one.

Router Default Boot Sequence for Cisco IOS

Router boot configuration commands

1. NVRAM
2. Flash (sequential)

boot system ROM : boots from system ROM
boot system flash : boots
IOS from flash memory
boot system tftp
: boots IOS from a tftp server

3. TFTP server
4. ROM

The router first looks at Startup Config file in NV
RAM,if not available, it falls back to Flash, then
to TFTP and then to ROM.

Configuration Register Command

Router modes of operation include

Router(config)# config-register 0x10x (where that last x is 0-F in hex), when the last x is: 0 = boot
into ROM Monitor mode; 1 = boot the ROM IOS; 2 - 15 = look in startup-config file in NVRAM.

Cisco router configurable locations

Router...