OSPF LSA AND AREA TYPES

OSPF LSA TYPES

LSA type 1 – Router LSA’s (Generated by each router)

LSA type 2 – Network LSA’s (Generated by DR)

LSA type 3 – Summary LSA’s (Generated by an ABR)

LSA type 4 – Summary LSA’s which advertises path to an ASBR to reach external networks. (Generated by an ABR)

LSA type 5 – External LSA’s which advertises external routes from another routing domain (Generated by an ASBR)

LSA type 7 – NSSA LSA, which allows an ASBR inside an OSPF stubby area, which will get converted to LSA type 5 at nearest ABR

OSPF AREA TYPES

1) Stub Areas – Allow only LSA type 1, 2 and 3 to propogate.

2) Totally Stub Areas – Allow only LSA type 1 and 2 to propogate. The ABR will inject a Defualt Route to the routers inside Totally Stub area.

3) NSSA Areas – Same as Stub, but allow LSA type 7 also to propogate. These type 7 LSA’s will get converted to type 5 LSA’s at nearest ABR.

4) Totally NSSA Areas – Same as Totally Stub areas, but allow LSA type 7 also to propogate. These type 7 LSA’s will get converted to type 5 LSA’s at nearest ABR. The ABR also will inject a Defualt Route to the routers inside Totally NSSA area.

5) Normal Areas - An area in which routers are connected usually, which allows all types of LSA.

6) Backbone Area - An area which connects two normal area , where all LSA's are supported

REMOTE ACCESS OF CISCO ROUTERS USING TELNET & SSH

Many have doubts on  how to get access of a Cisco router's Command Line interface through remote access protocols. Actually there are two such ways to get access remotely to a Cisco device. they are TELNET and SSH. 

TELNET stands for Teletype Network , which is a protocol used to get access to a remote device without encryption in data transfer . 

SSH  stands for Secured Shell, which is a cryptographic protocol used to get access to a remote device with encryption in data transfer . 

Among the two, the most secured way of access is SSH.

Now we are going to see a short and simplified tutorial on how to do these things. 

See the above topology, In that we have two routers R1 and R2. Among these we are going to access  R2 router from R1, using remote access protocols like TELNET and SSH.

Assign IP address for the interfaces Fa 0/0 of R1 with 10.0.0.1/8 and Fa 0/0 of R2 with 10.0.0.2 . Then proceed as directed below,

R2#conf t

R2(config)#hostname vignesh

You must also configure a domain name:

vignesh(config)#ip domain-name internetworkershub

Generate an RSA keypair with a key length of 1024 bits using the following sequence of commands:

vignesh(config)#crypto key generate rsa

The name for the keys will be: vignesh.internetworkershub (where vignesh is R2's hostname)Choose the size of the key modulus in the range of 360 to 2048 for your  General Purpose Keys. Choosing a key modulus greater than 512 may take a few minutes.How many bits in the modulus [512]: 512% Generating 512 bit RSA keys ...[OK]

Create a username in the router’s local database for SSH authentication using the following command

vignesh(config)#username admin secret p@ssword

Enable login authentication against the local database when logging in to a terminal line using SSH and TELNET with the following commands:

vignesh(config)#line vty 0 4vignesh(config)#transport input ssh telnetvignesh(config-line)#login local

Enable SSHv2 and the previously configured keypair with the following commands:

vignesh(config)#ip ssh version 2vignesh(config)#ip ssh rsa keypair-name vignesh.internetworkershub (where vignesh is your R2's hostname)

Attempt to login using SSH from other router R1 ,

R2# ssh -l admin -v 2 10.0.0.2 (where -l is login name, -v is version)
password : p@ssword
vignesh>
Now you got the access using SSH for R2 router which has hostname of vignesh.
Don't close the session instead press CTRL+SHIFT+6 ~ x to go to your router R1 again, now try accessing using TELNET

R1# telnet 10.0.0.2

User access verfication

Username :adminpassword:p@ssword
vignesh>

Now you got the access using TELNET for R2 router which has hostname of vignesh.
Don't close the session instead press CTRL+SHIFT+6 ~ x to go to your router R1 again.

R1# show sessions

Conn Host           Address       Byte  Idle Conn Name

   1 10.0.0.2      10.0.0.2         0     6 10.0.0.2

*  2 10.0.0.2       10.0.0.2         0     0

Telnet command will be supported by windows cmd . But,ssh will not be supported by cmd. so , you need tools like Putty to access using SSH from windows. In linux there is no problem both will work fine.

I believe, Now you guys know how to remotely access Cisco routers using telnet and ssh.

 

DIFFERENCES BETWEEN VIRUS, WORMS, RANSOMWARE, TROJANS, BOTS, MALWARE, SPYWARE.

Everyone might have a confusion on these terms like malware, virus, worms, Trojans, etc. we might wonder each time when we see our antivirus flush these stuffs out of the systems.

Who are they ? what they are going to cause?

To know the answer just scroll down.😉





Malware

Malware is the generic term for the software which carries the stuffs like Virus, Trojans, Ransomware, bots , spyware.etc

Worm

Worms are not harmful as you think but they are known for occupying the hardisk space. They are like spies with secret mission of replicating themselves in a large number and spreading to many computers as possible using networks. Their process of replication will happen without the knowledge of the users of the computer as they are as confidential as possible.

Virus

Unlike worms virus is going to affect files on the system thereby continuing their process of replicating . The only relief among users is that virus need coordination from the host program where it is attached  to replicate and infect files. Usually virus can be found attached to music, videos and other executable files .  They spread when we download or share content which is having virus in it.

There are many types of viruses , we will see one by one.

Boot Sector Virus
These virus are famous for deleting the master boot record and very difficult to remove. mostly the solution will be formatting the full system. They usually spread through removable media.

Direct Action Virus
It is easy to remove virus, and will not hide from the anti virus. They are not that much harmful.

Resident virus
Unlike direct action virus, they are going to install themselves automatically and replicates by themselves. they work when original source is eradicated . they are of two types (i.e) fast infector and slow infector. fast infector affects the files quickly and easier to be recognized. slow infector cannot be recognized easily and will not affect quickly. They have capabilities to attach to antivirus program and infects every file and program of the system.

Multipartite Virus
They are virus which uses all spreading methods possible. They can attack both boot sector and files.
once deleted from the system , they will regenerate from the boot sector after power on.

Polymorphic Virus
They are the challenge for any antivirus. Antivirus need to create routine of detection to detect a polymorphic virus. they change their binary pattern for each replication , so antivirus finds it as different virus therefore will not be found in blacklisted virus program.

Overwrite Virus
These type of virus has capabilities to delete any files or software which it has infected. to remove the virus the only way is to delete that file or software. They cannot be found nowadays, but prevails.

Space-filler Virus

They are also called as cavity virus, it is a rare type which attempts to install itself into a file by filling in the empty sections of a file. But problem is they file size will not differ making it difficult for a anti virus program to find it.

Trojan

Trojan's main aim is to provide backdoor entry for a malicious software  to get installed without our knowledge to steal data and valuables.

Adware

They are responsible for unwanted ads in computer's desktop and inside any software. They are attached to open source software to display ads to create and income.

Spam

Unwanted emails from unknown senders are spams or junks. They may contain some malware. They are they cause of  commercial advertisements through mails. 

Bot 

They may be called as intelligent worms who carry an automated process for attacking and infecting the entire host making them join a central server which is the command center for all bots . All such infected hosts connected to a Central command center form a network  called as botnet. Bot are created  with a lot hard work by the malignant creators. They provide way for other malicious applications such as key-loggers, network traffic analyzer and even can cause Denial of Service attack.

Ransomware

It is a type of malware which can attack a system and encrypts the files and make them inaccessible by  the owner or user of the system. They further display  a warning message that , if you need your access you should make a payment.

CIRCUIT SWITCHING (VS) PACKET SWITCHING

Circuit Switching

      Circuit Switching allows temporary connections to be established, maintained, and terminated between message sources and message destinations. For example in the case of the voice- based phone network with which most people are familiar, a call is routed through a central office piece of equipment known as a switch, which creates a temporary circuit between the source phone and the phone of the party to whom one wishes to talk. This connection or circuit only lasts for the duration of the call. This switching technique is known as circuit switching and is one of two primary switching techniques employed to deliver messages from here to there. In a circuit switched network, a switched dedicated circuit is created to connect the two or more parties, eliminating the need for source and destination address information such as that provided by picketing techniques.

            The switched dedicated circuit established on circuit switched networks makes it appear to the user of the circuit as if a wire has been run directly between the phones of the calling parties. The physical resources required to create this temporary connection are dedicated to that particular circuit for the duration of the connection. If system usage should increase to the point where insufficient resources are available to create additional connections, users would not get connected.

Packet Switching

               The other primary switching technique employed to deliver messages from here to there is known as packet switching. Packet switching differs from circuit switching in several key areas. First, packets travel one at a time from the message source through a packet switched network, otherwise known as a public data network, to the message destination.The physical path which any packet takes may be different than other packets and in any case, is unknown to the end users. 

              Remember that packets are specially structured groups of data, which include control, sequence, source address, destination address information in addition to the data itself. These packets must be assembled (control and address information added to data) somewhere before entry into the packet switched network and must be subsequently dis-assembled before delivery of the data to the message destination.