Routable and Routed Protocols

Hi,

I would be grateful if you could tell me the difference between routable and routed protocols.

What I have learned so far, and I may be wrong, is that a router uses routable protocols and that it is defined at layer 3 of the OSI model. I have also learned that the layer 3 of the OSI model uses routed protocols for data packets.

I having some difficulty to understand the difference between the routable and routed protocols.

Thank you.

Patrick Ng

Hi Patrick,

Your question seemed simple initially but when I thought about it carefully, I found myself a little bit of puzzled too!

As what I understand, routable protocols are protocols that can be routed between routers in layer 3 network. All routed protocols are routable.

In layer 3 operation, routed protocols are used to carry our data packets across the network. Examples of routed protocols are IP & IPX. Accidentally, before that can be done, routers need to determine the (best) routes in the network. In this case, it uses different protocols and that’s called routing protocol (eg, RIP, IGRP).

Yes, both routed and routing protocols are operated at layer 3 but I don’t know if I should classify routing protocols as routable protocols? Can anyone tell me?

NetBIOS is an example of non-routable protocol and it’s strictly for LAN.

Anyone can correct me if I’m wrong.

Hi Guys,

The terms "routeable" and "routed" seems to be used by a fair few people in IT industry to explain different characteristics of protocols or how routers work.

This has led to a confusion for most of us and as a result, its become somewhat unclear as to what we are talking about when we use these terms.

Let's get a few things in prospective to help us understand what term is used in each case.

Steelben, your right about the "Routing Protocols" term. Routers use "Routing Protocols" in order to find the best path to the destination which they want to send a packet. Routing protocols are used only by routers, servers or any host/device which needs to pass packets from one network to another. Routing protocols are usually found in WAN's and not so often within LAN's.

So in a WAN, the routers that connect between each other use these Routing Protocols to share information about the paths they know e.t.c. This information is NOT passed to the LAN's these routers might connect to.

On the other hand, a protocol is said to be "Routed" when it contains information that will allow it to triverse networks. As steelben said, this information is added to the protocol when it reaches the 3rd OSI layer, also known as the Network Layer.

A Non-routed protocol does not contain any Network Layer information, in plain english, its payload dosent have any information about the IP address to which the packet is surpose to goto.

NetBios is a prime example of a non-routeable protocol because it hasnt got any Network Layer information. If you check the RFC's for the protocol you will be able to clearly see this within the packet structure, or shall I say datagram structure.

This is also why all windows machines have the "Bind/Enable Netbios over tcp/ip" option in their network settings. This option uses TCP/IP to encapsulate Netbios and get it to its destination!

I Hope this helps clear up your questions. If I've got anything wrong, let me know! I'm only human [img]images/smiles/icon_smile.gif[/img]

Cheers Guys,

Hi Guys,

First of all thank you very much for devoting some of your precious time to reply to my message.

I understood quite well the routing protocols and was coming to the conclusion that all routed protocols are routable protocols. This has now been confirmed .

The reason of all this confusion in my head is that I was reading two books.

One about Networking +. In that book when talking about routers for the first time the author mentionned that routers rely on two types of protocols to make the "magic" happen. Routable and routing protocols. The author describes routable protocols as protocols capable of identifying networks as well as uniquely identify the hosts connected to these network, example given for a routable protocol is TCP/IP and IPX/SPX.

The second book I read was by Todd Lammle on CCNA. In that book at the OSI model layer 3, the author said that routers use routed protocols to move data packets and routing protocols for updates. Example given for routed protocol is IP. So it was then that everything started in my mind. I wanted to know the difference between routable and routed protocols as in my mind, routable protocols is the suite and IP is a routed protocol. Since IP is in the TCP/IP suite that means that IP is also a routable protocol. Am I right ?