In computer networking, what is the basic difference between routable and non routable protocols?

Introduction / Context:
When designing or troubleshooting networks, you may encounter the terms routable and non routable protocols. This classification affects whether traffic using a given protocol can pass through routers and reach remote networks or whether it must stay confined to a local segment. Understanding this distinction is important in both legacy networking environments and in understanding why some protocols work across networks while others are local only.

Given Data / Assumptions:

• We are comparing protocols that operate at or above the network layer.
• Routers forward packets based on network layer addressing, such as IP addresses.
• Non routable protocols historically lacked network layer addresses that routers could interpret.
• The question asks for the basic difference between routable and non routable protocols.

Concept / Approach:
A routable protocol includes network layer addressing and routing information in its packet format so that routers can examine the header and decide where to forward the packet next. Protocols like IP are routable because they include source and destination addresses and support routing tables. Non routable protocols do not provide network layer addressing that routers can use. As a result, they can be forwarded only within a single broadcast domain or must be encapsulated inside another routable protocol to travel between networks.

Step-by-Step Solution:
Step 1: Recall that routers operate at the network layer and make forwarding decisions based on network layer addresses.Step 2: Understand that a routable protocol must include network layer address fields and routing related information in its header.Step 3: Recognize that non routable protocols do not provide such addresses in a form that routers can interpret directly.Step 4: As a result, routers cannot forward pure non routable protocol frames to other network segments without additional encapsulation or tunneling.Step 5: Conclude that the main difference is the presence or absence of network layer addressing that enables routing across multiple networks.

Verification / Alternative check:
Historically, examples of non routable protocols include NetBEUI, which was intended for small local networks and did not support routing across multiple IP networks without encapsulation. In contrast, IP is designed as a routable protocol and is used throughout the Internet. Routers examine IP headers to determine paths, but they cannot do the same with non routable frames unless those frames are transported over IP or another routable protocol. This practical history supports the conceptual distinction.

Why Other Options Are Wrong:
Option B is incorrect because both routable and non routable protocols can appear in local area networks, and routable protocols are also used on the Internet. Option C is wrong because reliability is determined by transport layer or upper layer mechanisms, not by whether a protocol is routable. Option D is incorrect because the type of cable used is independent of whether a protocol is routable; both protocol types can run over copper or fiber as long as the underlying physical and data link layers support them.

Common Pitfalls:
Students sometimes confuse routability with security or quality of service, assuming that non routable protocols are more secure or higher quality simply because they are local. In reality, routability only indicates whether routers can forward the protocol based on network layer addressing. Another pitfall is thinking that non routable protocols are no longer relevant; they still appear in legacy systems and in theoretical discussions, so understanding the concept remains useful.

Final Answer:
The key difference is that routable protocols include network layer addressing so routers can forward them between networks, while non routable protocols lack such addressing and are confined to a single local segment.