Difference Between Classful Routing and Classless Routing

Classful and classless routing are two different ways through which the IP addresses are managed and structured in a network. Classful Routing is an older approach whereby the IP addresses are divided by fixed classes such as A, B, C, and the rest all with a preset mask. This way, the subnet mask information is not carried in routing updates and it is a simple system with less flexibility.

Classless routing, however, supports VLSM and thus allows variable-length subnet masking. This ensures that many IP addresses are efficiently utilized by carrying the subnet mask information in the routing updates. This provides greater flexibility and scalability and so is more appropriate for modern networks.

What is Classful Routing?

Classful Routing does not import subnet mask. In this also subnet mask is also provided after the route update. In classful routing, the subnet mask is the same throughout and does not vary for all devices, we can see it in the given picture. In classful routing, VLSM (Variable Length Subnet Mask) is not supported, and neither is CIDR (Classless Inter-Domain Routing).

Advantages of Classful Routing

Simplicity: Classful routing is simple and easy to understand; hence, it is relatively easier to implement and manage.
Compatibility: Most older routing protocols and devices support only classful routing; hence, it remains a standard in legacy systems.
Automatic Subnet Mask Assignment: Each class has a default subnet mask, which diminishes the need for manual configuration.

Disadvantages of Classful Routing

Classful Routing and Classless Routing

Inefficient IP Address Utilization: This technique of routing makes use of the concept of a fixed-size block of IP addresses, which again causes a wastage of address spaces.
Lack of Flexibility: It does not support VLSM—Variable Length Subnet Masking . Creation of the subnets is done on fixed-size blocks that are, at times, very large for the exact requirements.
Limited Scalability: Because of the rigid structure of classful routing, it might end up being inefficient in terms of IP address usage and managing larger networks when the networks start growing.

What is Classless Routing?

Classless Routing imports subnet mask and in this, triggered updates are used. In classless routing, VLSM (Variable Length Subnet Mask) is supported and also CIDR (Classless Inter-Domain Routing). In classless routing, hello messages are used for checking status. In classless routing, subnet mask is not same throughout, it may vary for all devices, we can see it in the given picture.

Advantages of Classless Routing

Efficient IP Address Utilization: Supports VLSM, allowing more efficient, finer-grain allocation of IP addresses without address space wastage.
Scalability: Enhanced flexibility in growing networks since created subnets exactly fit the number of necessary addresses to be used, thus very useful in large and complex networks.
Supports Modern Routing Protocols: This classless routing works well with modern protocols like OSPF and EIGRP , which are designed for efficient and dynamic routing.

Disadvantages of Classless Routing

Complexity: The classless routing requires more minute information on subnetting and IP address allocation. Hence, it can be configured and managed only with a greater degree of complexity.
Needs More Processing Power: The added burden of processing more detailed routing information, such as subnet masks, can be resource-intensive for routers.
Non-Compatibility with Older Systems: Classless routing capability may not be supported by older devices and protocols; hence, there are chances of incompatibility within a mixed environment.

Difference Between Classful Routing and Classless Routing

Classful Routing	Classless Routing
In classful routing, VLSM (Variable Length Subnet Mask) is not supported.	While in classless routing, VLSM (Variable Length Subnet Mask) is supported.
Classful routing requires more bandwidth.	While it requires less bandwidth.
In classful routing, hello messages are not used.	While in classless routing, hello messages are used.
Classful routing does not import subnet mask.	Whereas it imports subnet mask .
In classful routing, address is divided into three parts which are: Network , Subnet and Host .	While in classless routing, address is divided into two parts which are: Subnet and Host.
In classful routing, regular or periodic updates are used.	Whereas in this, triggered updates are used.
In classful routing, CIDR(Classless Inter-Domain Routing) is not supported.	While in classless routing, CIDR (Classless Inter-Domain Routing) is supported.
In classful routing, subnets are not displayed in other major subnet.	While in classless routing, subnets are displayed in other major subnet..
In classful routing, fault can be detected easily.	While in classless routing, fault detection is little tough.

Conclusion

Classful routing is easier and was adequate when IP address allocation was simpler, but it is profligate in IP address use and lacks scalability. Classless routing, supporting VLSM, permits very fine granularity in IP address allocation and is, therefore, much more desirable for today’s complex and large-scale networks.

Difference Between Classful Routing and Classless Routing – FAQs

What is the critical difference between classful and classless routing?

In classful routing, fixed subnet masks are used based on predefined IP address classes. It includes A, B, C classes. On the other hand, classless routing is variable-length and hence provides greater flexibility in the allocation of IPs.

Why is classless routing preferred over classful routing?

Classless routing is favored for a number of reasons: it is more efficient in terms of the usage of IP addresses; it supports subnetting; and it is scalable, which makes it more accommodative for large networks in use nowadays.

Can classful and classless routing be used together?

No, they are incompatible. Classful routing doesn’t include subnet mask information in routing updates, and classless routing depends on this information so that proper routing decisions are made.

Is classful routing still used today?

Classful routing is largely a deprecated scheme and very seldom in use today, because of inefficiency and due to the wide proliferation of the classless routing protocols like OSPF and EIGRP.

What are examples of classless routing protocols?

Examples for classless routing protocols include OSPF—Open Shortest Path First, EIGRP—Enhanced Interior Gateway Routing Protocol, and BGP—Border Gateway Protocol.

Does classless routing really improve IP address utilization?

Yes, classless routing does provide an improvement in IP address utilization because it allows just the number of IP addresses required by a given subnet to be used.