Routing protocols have far-reaching effects on the performance and reliability of your network, but sorting out the differences between them can be a challenge. Choose the best one for your network by taking a look at this detailed comparison.
Many of us work on networks we didn’t have the luxury of designing—with routing protocols we weren’t given the chance to choose. But you may be starting a new network, or you may have the opportunity to redesign your existing one. If you’re tasked with selecting the best routing protocol for your network, which will you choose?
While there is often a “right tool for the job,” all routing protocols have their strengths and weaknesses, and I don’t believe that there is a clear-cut best routing protocol that is the right tool for every network. Thus, to help you select the most appropriate routing protocol for your network, I am going to examine the pros and cons of the best-known routing protocols and offer some guidance on when it makes sense to use one or the other.
RIP V1—Routing Information Protocol
Origin: Based on RFC 1058
Type of protocol: Distance vector, based on the Bellman-Ford distance vector algorithm
Metric: Hop count
Methodology: Selects routers with the lowest hop count; updates other routers by broadcasting the entire routing table to all routers every 30 seconds
Ideal topology: Smaller networks that aren’t very dynamic, have fewer than 15 hops, and are not subnetted from classful boundaries (see Weaknesses)
Strengths:
Weaknesses:
RIP V2—Routing Information Protocol
Origin: Based on RFC 1388
Type of protocol: Distance vector, based on the Bellman-Ford distance vector algorithm
Metric: Hop count
Methodology: Selects routers with the lowest hop count; updates other routers by multicasting the entire routing table to all routers every 30 seconds
Ideal topology: Smaller networks that aren’t very dynamic, have fewer than 15 hops
Strengths:
Weaknesses:
IGRP—Interior Gateway Routing Protocol
Origin: Based only on Cisco’s implementation, not an Internet RFC
Type of protocol: Distance vector, based on the Bellman-Ford distance vector algorithm
Metric: Delay, bandwidth, reliability, and load
Methodology: Sends hello packets every five seconds to neighbors to see if the neighbor is still available; updates other routers by notifying them only when routes change
Ideal topology: Any network, small to very large; all routers must be from Cisco. Cannot subnet network beyond classful boundaries.
Strengths:
Weaknesses:
Convergence: The process that a routing protocol goes through to alert all routers on the network of the next available path when the primary path becomes unavailable.
EIGRP—Enhanced Interior Gateway Routing Protocol
: Based only on Cisco’s implementation, not an Internet RFC
Type of protocol: Hybrid distance vector
Metric: Delay, bandwidth, reliability, and load, using the Diffusing Update Algorithm (DUAL)
Methodology: Sends hello packets every five seconds to neighbors (can interoperate with IGRP) to see if the neighbors are still available; updates other routers by notifying them only when routes change
Ideal topology: Any network, small to very large; all routers must be Cisco
Strengths:
Weaknesses:
OSPF V2—Open Shortest Path First
[Note that version 1 of OSPF was never implemented.]
Origin: Based on RFC 2328
Type of protocol: Link-state, runs the Dijkstra algorithm to calculate the shortest-path first (SPF) tree
Metric: Calculates the cost to traverse router links to get to the destination, taking the bandwidth of the links into account
Methodology: Develops adjacencies with its neighbors, periodically sending hello packets to neighbors, flooding changes to neighbors when a link’s status changes, and sending “paranoia updates” to neighbors every 30 minutes of all recent link state changes
Ideal topology: Any network, small to very large
Strengths:
Weaknesses:
Final word
Just to clarify this comparison, one way routing protocols are classified is according to how they are used. Interior routing protocols are used within a single domain on your interior network. Also called an Interior Gateway Protocol (IGP), this is the type of routing protocol you usually think of using for your internal network. The protocols we looked at in this article are all IGPs. Note that I omitted a few of the lesser-known interior routing protocols to keep the discussion reasonably short. These include IS-IS, NLSP, RTMP, and IPX RIP.
Another type of routing protocol is an exterior routing protocol, or Exterior Gateway Protocol (EGP). These protocols maintain routing information for networks that are external to your network. An EGP doesn’t know how to deliver data within your network, just how to deliver data outside your network. While a variety of IGPs are currently used, about the only EGP in use today is the Border Gateway Protocol (BGP). This is the routing protocol of the Internet.
From talking with administrators who manage a variety of networks, the consensus is that OSPF is becoming the most popular interior routing protocol today. I would recommend OSPF or EIGRP for any new network, based on their popularity, flexibility, and fast convergence. Of course, the choice is yours based on the requirements of your network. This article should help you get a better understanding of your options.
Additional references
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