In networking, there is often terminology used to refer to various concepts that sound similar. This can occasionally be confusing especially to greener techs that are just coming into the field. One particular distinction that can potentially perplex less experienced networking professionals is the difference between routed and routing protocols.
In this article, we’ll help to clarify the meaning of the terminology used to clear up any misunderstandings concerning the meanings of these terms.
Context of Discussion
Networking is a broad field, and terms like “routing” and “routed” can refer to multiple concepts and approaches.
Both routing and routed protocols are primarily related to the Network Layer of the OSI model.
Therefore, for the purposes of this article, we will confine our discussion to the realm of TCP/IP where the primary Network Layer protocols being used are IPv4 and IPv6.
What Are Routing Protocols
Let’s start with routing protocols, as this term is much more well-defined, as you will see later on. Routing protocols are used by routers to dynamically discover, advertise, and learn about routes to specific networks.
These protocols allow routers to communicate and share routing information with each other to determine the best path that should be traveled for any particular destination.
Routing protocols define how routers communicate, what information they share, the algorithms that are used to determine the best path, and additional configuration parameters that can enable things like equal cost load balancing as well as backup routes.
The fundamental purpose of routing protocols is to allow a router to create a routing table. A routing table is a construct that is maintained in the memory of a router, that lists the destination networks that the router has learned about.
For each entry, it also defines a next-hop address and/or an exit interface. So when a router receives an IPv4 or IPv6 packet, it examines the destination address, and compares it with the entries in the routing table. When it finds a match, it knows where to send that packet based on the next hop IP or the exit interface.
A router may run multiple routing protocols and may learn about routes to destinations from multiple sources. The following is an example of a routing table found within a Cisco IOS router that has entries learned from multiple routing protocols including routes learned via OSPF as well as EIGRP:
Router# show ip route
Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2, E – EGP
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route, H – NHRP, l – LISP
a – application route
+ – replicated route, % – next hop override
Gateway of last resort is 10.0.0.1 to network 0.0.0.0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.1, 00:00:03, GigabitEthernet0/0
C 192.168.1.0/24 is directly connected, GigabitEthernet0/1
L 192.168.1.1/32 is directly connected, GigabitEthernet0/1
D 10.1.2.0/24 [90/30720] via 192.168.2.2, 00:00:03, GigabitEthernet0/2
O 10.1.3.0/24 [110/229840] via 192.168.3.2, 00:00:03, GigabitEthernet0/3
C 10.0.0.0/8 is directly connected, GigabitEthernet0/0
L 10.0.0.2/32 is directly connected, GigabitEthernet0/0
Examples of routing protocols include RIP (Routing Information Protocol), OSPF (Open Shortest Path First), EIGRP (Enhanced Interior Gateway Routing Protocol), BGP (Border Gateway Protocol), and IS-IS (Intermediate System to Intermediate System), to name the most prominent.
What Are Routed Protocols
Routed protocols on the other hand, are those protocols that actually carry user data to its destination. They are the protocols used to send user data from source to destination.
They carry the user data and can be used to transport traffic between different networks. Typically, routed protocols exist within the Network Layer of the OSI model, but they may also be part of upper-layer protocols depending on your definition of the term.
Examples of routed protocols at the Network Layer include IPv4 and IPv6, but can also include others such as IPX and AppleTalk.
The two latter protocols are no longer in any substantial usage, but are just listed here for completeness.
Routed protocols are responsible for transporting user data, and are involved in the process of encapsulation, where data from the application layer of the OSI model is wrapped in headers from each subsequent layer.
The routed protocol headers contain the destination address that is then leveraged by routing protocols to decide how to get the packet to its intended destination.
The Difference Between Routed vs Routing Protocols
The key difference between the two is in their roles within a network.
Routed protocols are used to transmit user data, while routing protocols are used to determine how that data gets successfully to its destination.
Another way of looking at it is that routing protocols function on the control plane, where communication takes place between intermediary network devices (such as routers) for the purpose of enabling the operations and functionality of the network, while routed protocols function on the data plane, where the source and destination of such data are the actual hosts that are being served by the network.
Issues Involved in this Terminology
One of the problems with this comparison is the fact that we are not comparing two equal things. We’re kind of comparing apples to oranges.
Why? Well, routing protocols are a well-defined group of protocols that perform a specific function. As mentioned before, these include OSPF, EIGRP, IS-IS, BGP, and RIP, to name the most prominent ones. These are further subdivided into distinct categories based on how they operate.
On the other hand, the term “routed protocol” is a somewhat more loosely used term to refer to those protocols that are served by routing protocols.
There’s no standardized list of such protocols, although the most commonly referred to routed protocols include IPv4, IPv6, IPX and AppleTalk as mentioned before.
However, some may also consider higher layer protocols to be routed as well, such as TCP, UDP, HTTP, and FTP, since these too depend upon routing protocols to be routed over the network. But this depends on your definition of the term.
For this reason, you will most likely come across the term “routing protocols” much more often than “routed protocols,” the former being much more well-defined, while the latter may have various meanings depending upon the context.
|Routing Protocols||Routed Protocols|
|Examples include OSPF, EIGRP, RIP, IGRP, IS-IS||Examples include IPv4, IPv6, IPX, Appletalk|
|Allow routers to determine the best path to reach a destination network.||Are used to deliver user data to hosts being served by the network.|
|Based on routing algorithms (running on the network routers) in order to help the routers build their routing table.||Based on an addressing scheme (e.g IP address) to identify each host/node on the network,|
|Help the Routed Protocol to successfully find the destination of a packet.||They are directed by a routing protocol in order to deliver data packets.|
As with many concepts in networking, the context from which you are describing things plays an important role in understanding.
Routing protocols are well-defined control plane entities that allow routers to determine the best path to reach a particular network.
Routed protocols on the other hand operate on the data plane and deliver user data to hosts being served by the network. Routed protocols depend upon routing protocols to get their data where they want it.
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