Routing Protocols Charles Warren

What is Routing? Routing refers to the process of taking a packet from one device and sending it through the network to another device on a different network. Static Routing - Harder to manage on a large scale, simpler to implement on few devices. Dynamic Routing - Easier to implement on a large network.

Static Routing Static routes can be used for specific instances such as breaking a general flow of traffic or configuring a gateway of last resort. Ex. ip route 0.0.0.0 0.0.0.0 192.168.1.254 This example says that if a route is unknown this device will send all traffic to the common interface associated with the IP 192.168.1.254

Dynamic Routing The first split in the dynamic protocol branch is the division of interior gateway protocols (IGPs) and exterior gateway protocols (EGPs). Interior Gateway Protocols Exterior Gateway Protocols

Interior Gateway Protocols IGPs deal with traffic that is contained within a single autonomous system or the same administrative domain. Routing protocols are broken into two different categories: Distant Vector: RIPv1 & 2, IGRP Link State: OSPF, IS-IS Distance Vector: Each time a packet goes through a router, it equals something we call a hop, and the route with the fewest hops to the destination network will be chosen as the best path to it. Link State: Using link state protocols, also called shortest path first protocols, the routers each create three separate tables. One of these tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the actual routing table.

RIP v1 & v2 Routing Information Protocol RIP uses only one thing to determine the best way to a remote network—the hop count. With default settings RIP only supports 15 hops to try and optimize routes. It functions by sending out a complete routing table out of all active interfaces every thirty seconds. This is the epitome of a distance vector protocol. Vocab: Classful and Classless: refers to if networks can be of VLSMs. VLSMs: Variable Length Subnet Masks. Remember that if a “classful routed network” requires that all subnet masks be the same length, then it follows that a “classless routed network” would allow us to use Variable Length Subnet Masks (VLSMs).

OSPF Open Shortest Path First Open Shortest Path First (OSPF) is an open-standard routing protocol that’s been implemented by a wide variety of network vendors. First, a shortest-path tree is constructed, and then the routing table is populated with the resulting best paths. OSPF converges quickly (although not as fast as EIGRP), and it supports multiple, equal-cost routes to the same destination.

EIGRP Enhanced Interior Gateway Routing Protocol EIGRP is a classless, enhanced distance vector Cisco proprietary protocol. Neighbor Table: Stores the address and interface of common interfaces Topology Table: Contains all destinations advertised by neighboring routes Feasible Successors / Successor: Holds paths whose reported distance is less than the feasible (best) distance, and it is considered a backup route. The best route is known as the successor.

IS-IS Intermediate System-to-Intermediate System IS-IS is a link state routing protocol, meaning it operates by reliably flooding topology information throughout a network of routers. Each router then independently builds a picture of the network’s topology, just as they do with OSPF. Level 1 intermediate systems route within an area. When the destination is outside an area, they route toward a Level 2 system. Level 2 intermediate systems route between areas and toward other ASs.

Exterior Gateway Protocols EGPs bridge the gap between different administrative domains. ISPs use BGP for its ability to make classless routing and summarization possible. These capabilities help to keep routing tables smaller and more efficient at the ISP core. We will be touching on these more at a later date, but for now these are not of concern to us