Routing & Switching: Routing Protocols | CompTIA Network+ N10-007 | 1.3c

In this video you will learn about routing protocols such as: distance-vector, link-state, hybrid, static, dynamic, & default protocols.

Routing Protocols

A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes on a computer network.  Routers perform the traffic directing functions on the Internet; data packets are forwarded through the networks of the internet from router to router until they reach their destination computer.  Routing algorithms determine the specific choice of route.  Each router has a prior knowledge only of networks attached to it directly.  A routing protocol shares this information first among immediate neighbors, and then throughout the network.  This way, routers gain knowledge of the topology of the network.  The ability of routing protocols to dynamically adjust to changing conditions such as disabled connections and components and route data around obstructions is what gives the Internet its fault tolerance and high availability.

Routing Protocols

Distance-Vector Routing Protocol

A distance-vector routing protocol in data networks determines the best route for data packets based on distance.  Distance-vector routing protocols measure the distance by the number of routers a packet has to pass, where one router counts as one hop.  Some distance-vector protocols also take into account network latency and other factors that influence traffic on a given route.  To determine the best route across a network, routers, on which a distance-vector protocol is implemented, exchange information with one another, usually routing tables plus hop counts for destination networks and possibly other traffic information.  Distance-vector routing protocols also require that a router informs its neighbors of network topology changes periodically.

Distance-Vector Routing Protocol
  • RIP (Routing Information Protocol)
    • The Routing Information Protocol is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric.  RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination.  The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support.
Routing Information Protocol
  • EIGRP (Enhanced Interior Gateway Routing Protocol)
    • Enhanced Interior Gateway Routing Protocol is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration.  The protocol was designed by Cisco Systems as a proprietary tool, available only on Cisco routers.  Functionality of EIGRP was converted to an open standard in 2013.  EIGRP is used on a router to share routes with other routers within the same autonomous system.  Unlike other well known routing protocols, such as RIP, EIGRP only sends incremental updates, reducing the workload on the router and the amount of data that needs to be transmitted.  EIGRP ultimately eases the workload on a network administrator so they don’t have to configure changes to the routing table manually.

Link-State Routing Protocols

Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the other being distance-vector routing protocols.  The link-state protocol is performed by every switching node in the network.  The basic concept of link-state routing is that every node constructs a map of the connectivity to the network, in the form of a graph, showing which nodes are connected to which other nodes.  Each node then independently calculates the next best logical path from it to every possible destination in the network.  Each collection of best paths will then form each node’s routing table.  This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors; in a link-state protocol the only information passed between nodes is connectivity related.  Link-state algorithms are sometimes characterized informally as each router, “telling the world about its neighbors.”

Link-State Routing Protocol
  • OSPF (Open Shortest Path First)
    • Open Shortest Path First is a routing protocol for Internet Protocol (IP) networks.  It uses a link-state routing algorithm and falls into the group of interior gateway protocols, operating within a single autonomous system.  Routing protocols like OSPF calculate the shortest route to a destination through the network based on an algorithm.
OSPF Protocol

Hybrid Routing Protocol (HRP)

Hybrid Routing Protocol, commonly referred to as balanced-hybrid routing, is a combination of distance-vector routing, which works by sharing its knowledge of the entire network with its neighbors and link-state routing which works by having the routers tell every router on the network about its closest neighbors.  Hybrid routing protocols use distance-vectors for more accurate metrics to determine the best paths to destination networks, and report routing information only when there is a change in the topology of the network.  Hybrid routing allows for rapid convergence but requires less processing power and memory as compared to link-state routing.

  • BGP (Border Gateway Protocol)
    • Border Gateway Protocol is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems on the Internet.  BGP is classified as a path-vector routing protocol, and it makes routing decisions based on paths, network policies, or rule-sets configured by a network administrator.
    • Another way to think about BGP is to think of it as the postal service of the Internet.  When someone drops a letter into a mailbox, the postal service processes that piece of mail and chooses a fast, efficient route to deliver that letter to its recipient.  Similarly, when someone submits data across the Internet, BGP is responsible for looking at all of the available paths that data could travel and picking the best route, which usually means hopping between autonomous systems.
BGP Protocols

Routing Types

Static Routing

Static routing is a form of routing that occurs when a router uses a manually-configured routing entry, rather than information from dynamic routing traffic.  In many cases, static routes are manually configured by a network administrator by adding entries into a routing table, though this may not always be the case.

Static Routing
  • Advantages
    • No routing overhead for router CPU which means a cheaper router can be used to do routing.
    • It adds security because only administrators can allow routing to particular networks only.
    • No bandwidth usage between routers.
  • Disadvantages
    • For a large network, it is a hectic task for an administrator to manually add each route for the network in the routing table on each router.
    • The administrator should have good knowledge of the topology.  If a new administrator comes, then he has to manually add each route so he should have very good knowledge of the routes of the topology.

Dynamic Routing

Dynamic routing is a process where a router can forward data via a different route or given destination based on the current conditions of the communication circuits within a system.  The term is most commonly associated with data networking to describe the capability of a network to ‘route around’ damage, such as loss of a node or a connection between nodes, so long as other path choices are available.  Dynamic routing allows as many routes as possible to remain valid in response to the change.

Dynamic Routing
  • Advantage
    • Easy to configure.
    • More effective at selecting the best route to a destination remote network and also for discovering remote networks.
  • Disadvantages
    • Consumes more bandwidth for communicating with other neighbors.
    • Less secure than static routing.

Default Routing

Default routing is a configuration of the Internet Protocol that establishes a forwarding rule for packets when no specific address of a next-hop host is available from the routing table or other routing mechanisms.  The default route is generally the address of another router, which treats the packet the same way:  if a route matches, the packet is forwarded accordingly, otherwise the packet is forwarded to the default route of that router.  The device to which the default route points is often called the default gateway, and it often carries out other functions such as packet filtering, or proxy server operations.

Default Routing