Category - blog

What is an IP classful and classlessnetwork

Classful addressing: 

In the classful addressing system  all the IP addresses that are available are divided into the five  classes A,B,C,D and E, in which class A, B and C address are frequently  used because class D is for Multicast and is rarely used and class E is  reserved and is not currently used. Each of the IP address belongs to a  particular class that’s why they are classful addresses. Earlier this addressing system did not have any name, but when classless addressing system came into existence then it is named as Classful addressing system. The main disadvantage of classful addressing is that it limited the flexibility and number of addresses that can be assigned to any device. One of the major disadvantages of classful addressing is that it does not send subnet information but it will send the complvce network address. The router will supply its own subnet mask based on its locally configured subnets. As long as you have the same subnet mask and the network is contiguous, you can use subnets of a classful network address.


1) In Classful addressing, it divides IP address into network ID and host ID

for example, Class A:- has the first octet as network ID and last three octets as Host ID

Class B:- has first two as network ID and last three two as Host ID

Class C:- has first three as network ID and last  octet as Host ID

2) Here class A, B, and C are used whereas class D is used for multicasting and class D for research

3) The disadvantage is that it limits the number of networks that can be provided to the network

4) Example RIP(Routing Information Protocol) protocol uses classful addressing

5) Class A: \8 as (1 octet is network ID), Class B:-\16 , Class C: \24

6) The same Subnet mask is used in complvce network


Classless Addressing:

Classless addressing system is also known as CIDR(Classless Inter-Domain Routing). Classless addressing is a way to allocate and specify the Internet addresses used in inter-domain routing more flexibly than with the original system of Internet Protocol (IP) address classes. What happened in classful addressing is that if any company needs more than 254 host machines but far fewer than the 65,533 host addresses then the only option for the company is to take the class B address. Now suppose company needs only 1000 IP addresses for its host computers then in this (65533-1000=64533) IP addresses get wasted. For this reason, the Internet was, until the arrival of CIDR, running out of address space much more quickly than necessary. CIDR effectively solved the problem by providing a new and more flexible way to specify network addresses in routers. A CIDR network address looks like this:


1) It allows us to use variable-length subnet mask so also known as VLSM (Variable Length Subnet Mask)

2) Different subnet mask used in the same network.

3) In this, there is no boundary on host id and network id

4) Classless Addressing also is known as CIDR(classless interdomain routing)

5) There is no default subnet mask in classless routing.

6) Example: BGP(Border Gateway Protocol), RIPv2


What is ROMMON mode

If you have worked with Cisco devices for some time, you must have heard about ROMMON or ROM Monitor.

ROMMON or also known as bootstrap program is you can say a mini operating system in the Cisco devices that helps to initialize the processor hardware and boot the operating system software (Cisco IOS).

  • It’s the mode that allows you change the configuration registry and most commonly used to recover login password

Difference between L2 VPN and L3 VPN

If you want to access the specific resources, you need to use L3 VPN.
If you want to access the entire resources, you need to use L2 VPN.


Example 1: 

With a L2 VPN, site A and site B, look act and feel like they are on the common L2 network together.   A router at site A can be an OSPF neighbor with a router at site B, as they appear directly connected.

With a L3 VPN, we don’t have a direct connection between sites at L2.    With a L3 VPN, we peer with the SP edge, and by learning routes from the SP, we have L3 connectivity between sites A and B.


Example 2:

Purpose of both the way of VPN connectivity is same, to connect two different site. The only difference is the way we connect both the site together for intercommunication.

In both the VPN stlye we use Service provider network to traverse from one site to other.

L3 VPN: Here we make direct connectivity with edge device of service provider, and this we have to do at both the end. Next we have to share our local routes with Service provider, which eventually transmitted to the other end of your VPN (i.e. your other site). So here service provider knows about our local routes. This way both the site have each others routes, making it L3 connectivity (As we have L3 routes)

L2 VPN: Connectivity in L2 VPN looks like both the site are on same L2 network together. To achive this Service provider make a predefined virtual connection in their network, known as pseudowire connection, between your two sites. So here we don’t have to share our local routes with service provider, so service provider stays transparent with about our internal routes. In L2 VPN communication happens in the same way we do at our single site local network.

Copyright ©2010 - 2022 | Privacy Policy | Terms & Conditions