Studying for CCNA
OSI Model
7
Layers (7 - Application, 6 - Presentation, 5 - Session, 4 - Transport, 3 -
Network, 2 - Data Link, 1 - Physical)
Differences between
HUB and Switch
HUB
= 1 Single Collision Domain
HUB
= 1 Single Broadcast domain
HUB
= Half Duplex
HUB
= Works at the Physical layer of the OSI model, sends signals
Switches
= each port is a separate collision domain
Switches
= have a single Broadcast domain if no VLANs are configured
Switches
= Full Duplex
Switches
uses ASICS chips allows
Switches
= Creates a CAM (Content Accessible Memory) table where all MAC addresses is
stored
Switches
work at the Data Link Layer of the OSI model sends phases
Type of Communications
Unicast
= One to one communication between source and destination
Broadcast
= A communication which is sent to all devices connected to a Network segment
Multicast
= A communication which is sent to a group of devices
ARP (Address Resolution Protocol) =
Broadcast message
Connecting to switch
to configure
Open
putty
Click
on "Serial"
Connection
Settings
Baud
Rate = 9600
Data
Bits: 8
Parity:
none
Stop
bit: 1
Flo
Control: none
Cisco Command modes:
User
EXEC mode - Switch - > (BAsic mode)
Enable
- Privileged EXEC mode - switch# (Full access)
Config
terminal - Global Configuration Mode – Switch (config)# (Full Configuration
Mode)
Configure Cisco Switch
Setup switch name:
# hostname
switch1
Set Switch's IP address for Management
You
need to setup the IP for the default VLAN, or VLAN interface 1
# interface
vlan 1
# ip
address 192.168.1.1 255.255.255.0
# no
shutdown
Setup default gateway at Global Config
Mode
# ip
default-gateway 192.168.1.1
Saving Configuration
# copy
running-config startup-config
How to show the version of IOS running
# show
version
Protecting User Privileged mode
Note: this is not secure
# enable
password cisco123
# enable
secret cisco1234
Note: this password is
encrypted within the configuration file
If
you have enable password and enable secret, enable secret will override enable
password
If you have enable password set, just
remove it with
# no enable
password
Password protect your Console mode
# line
console 0
# password
cisco123
# login
Set password for telnet
# line vty
0 4
# login
# password
cisco123
# service
password-encryption (to encrypt all passwords)
# banner
motd C
#################
Private
#################
C
Setup SSH
# username
renato password cisco1234
# ip
domain-name e-networks4real.co.uk
# crypto
key generate rsa 1024
# ip ssh
version 2
# line vty
0 4
# transport
input ssh
Port Security
How
many devices can be plugged onto each port? If anyone plugs a different device
port is disabled
# Show ip
interface brief
How to show all messages displayed on
the terminal
# Terminal
monitor
MAC address security
#
switchport mode access
#
switchport port-security
#
switchport port-security maximum 1
#
switchport port-security violation
#
interface fastEthernet 0
# show
port-security interface fastethernet <port>
Duplex mismatch
# interface
fastethernet 0/2
# speed 100
# duplex
full
Fixing console text wrapping
# line
console 0
# logging
synchronous
# line vty
0 4
# logging
synchronous
Setting IDLE time
# line console
0
#
exec-timeout 30 0
# line
vty 0 4
#
exec-timeout 30 0
Fixing Domain resolution annoying
problem
# no ip
domain-lookup
Troubleshooting Cisco Switches
# Show ip
interface brief
# show
interface fastEthernet 0/2
tx
load = Sending data
rx
load = receiving data
5
min input rate
5
min output rate
High
level of broadcast is considered to be 20%
Runt
is a packet considered to be too small
Late
collision means the cable length is greater than 100M
Check
for duplex mismatch
# show run
Type of Wireless
Networks
PAN
- Personal Area Network
LAN
- Local Area Network
MAN
- Metropolitan Area Network
WAN
- Wide Area Network
Wireless
is shared and Half-Duplex
The
more people connected the less Bandwidth available
Uses
Unlicensed BANDS of Radio Frequency (RF)
WIFI
operates at the Physical and Data Link layer of OSI model
WIFI
uses CSMA/CA (Carrier Sense Multiple Access/Collision Avoidence
Interference
is a problem and causes connectivity issues
WIFI Frequencies
·
900MHZ Range - 902 - 928
·
2.4-6GHz Range - 2.400 - 2.483
·
5-gGHz Range - 5.150 to 5350
The
lower Frequency the bigger is the range but the bandwidth is also low
Higher
frequency supports higher data rate
WiFi Standards
802.11B
1999
Up
to 11Mbps
2.45GHz
Three
channels
802.11A 1999
Up
to 54Mbps
5.8GHz
12 -
23 Channels
802.11G
2003
54Mbps
2.4GHz
Three
channels
802.11N
100+Mbps
using MIMO and multiple antenas
WIFI Channels
Range of Frequencies
The
channel defines a section of the 2.4GHz range of frequency
If
AP are in the same channel they will cause conflict and
802.11B
3 Clean Channels
802.11A
up to 23 Channels considered Clean or not overlapping
300Feet
without obstructions on the way
ITU-R
IEEE
WI-FI
Alliance
WIFI Security
Remember
it is an open door to the world
Authentication
Encryption
Intrusion
Prevention System
Pre-shared
key WEP (Use the same key)
Pre-shared
keys WPA1 using encryption methot called TKIP
WPA
and 802.1x Authentication (standard to request username and
Password
or pass-through to a server for checking the credentials)
WPA2
(802.11I) and 802.1x
SSID
(Service Set Identifier)
* Multiple
SSIDs
*
Used for public
*
used for internal or private
RF
10-15% overlaps in your frequency area
Repeaters
should have around 50%
BSS
Basic Service Set (Roaming with service drop)
ESS
Extended Service Set (Roaming without service loss)
Setting up redundant links
We
need to use spanning tree protocol
Ports
Well
known ports are 1-1023
A
socket is a combination of an IP address plus a port number:
192.168.20.22:80
Clients
use ramdon ports above 1024 as their source ports for example:
192.168.33:55667
Important Port
Numbers
20:
FTP
21:
FTP
22:
SSH
23:
TELNET
25:
SMTP
53:
DNS
80:
HTTP
110:
POP3
443:
HTTPS
69:
TFTP
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