Friday, October 24, 2014

Discussion

OSI Reference Model

Network Cabling Standards


IPv4 - IP Addressing


STP - Spanning Tree Protocol



VTP - VLAN Trunking Protocol

OSPF Network Types

OSPF Router Types

Important Port Numbers

Cisco Network Interview Questions

2950 Password Recovery

GNS3 Labs - Static route



GNS3 Labs - Default route


Saturday, October 4, 2014

Spanning Tree Protocol

STP helps to prevent loops in switched network. It works by selecting one root bridge, every non root bridge will select one root port and each network segment will select one designated port.  For selecting the root bridge it has some criteria’s first it will check the priority, if the priority is same it will check the Lowest MAC address and it will elected as a root bridge.

Root Port: Lowest path cost to root bridge, if cost is same lowest sender bridge ID (MAC)

Designated Port: Lowest path cost to root bridge, if cost is same lowest sender bridge ID (MAC)

 1. Lowest Bridge ID
 2. Lowest path cost to root bridge
 3.Lowest sender bridge ID
 4.lowest port priority
 5.Lowest Port ID.


Default Priority is 32768

STP and RSTP Difference


States:
STP                              RSTP

Disabled                              
Blocking                               Discarding
Listening                             
Learning                               Learning
Forwarding                           Forwarding              

RSTP will wait for 3 missed BPDU’s then it will go to learning to forwarding state


STP Convergence:

(Hello = 2 Sec)
Max Age (Blocking) = 20 secs
Listening = 15 secs
Learning = 15 secs
2*forward Delay +Max Age (2*15+20) = 50 secs to convergence


RSTP Convergence:

3 missed BDPUs @ 2 sec each = 6 secs
Learning (no listening) = 15 secs
= 21 secs to convergence


OSI Reference Model



It’s a logical model which is allowing us to think about where the problem may be. If we don’t know about the problem it will give us the idea where to start.

(It helps us to identify the problem and issue is related to which layer and from where to start the troubleshooting etc.)

Application ----- Where users are interacting with the information (like IE, Chrome etc.., ) If any issues with applications like IE or Chrome is not working it will be called as application layer problem.

Presentation ----- User interact with Application Layer it will sends the information to Presentation Layer it will convert it to system level language (conversion and Compression), OS will work at this layer. If any issues with drivers or OS (corrupted) issues it will be called as presentation layer problem.

Session ----- It will deals with the communication between two computers, it will create the session between source computers to destination computer.

Transport ---- It will decide how much communication we can able to communicate with the client and how much information client can communicate with us. This layer is responsible for delivering the packets at the destination.

Network ---- This is the layer were router will work based on IP address. It will decide the route to (Best path) reach the destination.

Data Link ---- Switch will work at this layer based on MAC Address, Layer 2 switching LLC and MAC layer will work at this layer.


Physical ----- All the physical stuffs which connects to the computer to network. Like cables, patch card, etc… There is no configuration at this layer.

Network Cables

Types Of Cabling

Straight Cabling - To connect Different Systems
Crossover Cabling - To connect Similar Devices
Rollover Cabling - To connect Aux port


STRAIGHT CABLE STANDARD 

OW                  OW
O                     O
GW                  GW
G                     G
BW                  BW
B                     B
BrW                 BrW
Br                    Br

CROSS CABLE STANDARD

OW                   GW
O                      G
GW                   OW
B                      B
BW                   BW
G                      O
BrW                  BrW
Br                     Br



ROLLOVER CABLE STANDARD

OW                   BrW
O                      Br
GW                   BW
G                      B
BW                   GE
B                      G
BrW                  OW
Br                     O

Pins 1, 2, 3, 6 are crossed to  3, 6, 1, 2 in cross cable respectively

OW - Orange White
O    - Orange
GW - Green White
G    - Green
BW - Blue White
B   - Blue
BrW- Brown White
Br  - Brown

IP Addressing - IPV4

Internet Protocol address, an IP address is an address of a computer or other network device on a network using TCP/IP.

Five classes of available IP ranges:

Class A - 1.0.0.1 to 126.255.255.254 - Supports 16 million hosts & 127 networks

Class B - 128.1.0.1 to 191.255.255.254 - Supports 65,000 hosts & 16,000 networks

Class C - 192.0.1.1 to 223.255.254.254 - Supports 254 hosts & 2 million networks

Class D - 224.0.0.0 to 239.255.255.255 - Reserved for multicast groups

Class E - Reserved for future use & Research and Development Purposes


Class A, B & C are commonly used