It’s important to remember that a routed protocol is not the same as a routing protocol. When thinking about routed protocol, the first and only thing that should come to mind is IP, the most widely and commonly used routed protocol today. With IP, routers are able to identify and deliver data packets.
In some cases a data packet may not belong on a certain network. When this occurs, routers use routing tables to decide what should be done with the packet. The routing tables used are created using specific routing protocols. To be successful in section 1.5, it’s important to know of the basic routing protocols and how each of them functions on a network.
- Link state Link state is the most commonly used type of routing protocols. These routing protocols are able to identify information about a packet including what it’s connected to, where it is, the speed of it, and so on. Using link state protocols, all of this information is sent in LSAs (link state advertisements) and using the LSAs, routers are able to build a network map. Each router will have the same map and is therefore able to decide what should be done with the packet.
- OSPF – Open shortest path first (OSPF) is the go to link state routing protocol as it is suitable for all network types and sizes. Looking at its name, it’s safe to assume that the protocol is an open protocol that uses the SPF algorithm and isn’t proprietary. OSPF is so widely used because it is able to converge on a network even when a sudden change occurs which means that when a routing table needs to be changed, the action can be completely quite quickly when using OSPF. Usually the change takes no more than a few seconds.
- IS-IS – Intermediate system to intermediate system (IS-IS) is not a commonly used link state routing protocol today. IS-IS too uses the SPF algorithm in order to decide where a packet should be delivered but the system uses a complex level system in order to obtain network topology. IS-IS, in the past, has been used by large service providers but rarely government or commercial networks.
- Distance vectorThe name describes the basic function of distance vector protocols. In this case distance refers to how far a packet needs to go and vector goes along with determining the direction of said packet. Distance and direction are both observed and compared against routing tables when using distance vector protocols.
- RIP – Routing information protocol (RIP) today is mostly obsolete though it does stand as the first distance vector ever created and used, but today it has since been replaced by RIPv2, OSPF, and other routing protocols. RIP works by having the routers broadcast the information they know regarding the network every 30 seconds, the main fallback with the protocol. RIP is also classful and the hop count used is severely flawed, therefore making it unusable for efficient network management.
- RIPv2 – Routing information protocol version 2 (RIPv2) is the more improved version of RIP. The protocol was able to fix some of the biggest flaws with RIP but it still does not perfect the original protocol. RIPv2 does not broadcast every 30 seconds and instead uses multicast addressing which makes the protocol much more efficient. Unlike RIPv1, RIPv2 can be made to be classless which means it can be used on a more complex network. The only flaw that exists is the fact that RIPv2 still uses a hop count.
- BGP – Border gateway protocol (BGP) is not a widely discussed topic on the Network+ exam. For your own knowledge, it may be important to know that BGP can be used on an autonomous network where all network devices are under the same control no matter of their location. Connecting to the Internet is an example of BGP.
- Hybrid There is only one notable hybrid routing protocol worth knowing for the Network+ test, EIGRP. As a hybrid routing protocol, EIGRP is truly a distance vector but it acts and works like a link state protocol.
- EIGRP – Enhanced interior gateway routing protocol, combines both technologies of distance vectors and link state protocols. EIGRP is a very advanced protocol because it is a hybrid and makes great use of the fast convergence of link state protocols. EIGRP does not use a hop count; instead it uses a metric that involves the bandwidth and delay of a connection, meaning how much time traffic needs to travel on a network path. The only downfall with EIGRP is that it is a Cisco proprietary and can only be used on Cisco routers and switches.
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