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Network+(N10-005) Cram Notes

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1.4 Explain the purpose and properties of routing and switching.

Routing is the process of directing the messages generated at source host towards the destination host over a computer network. The path may consist of several nodes that forward the messages (packets) towards the destination. Due to complexity of the protocols, and user requirements, several routing protocols have come in to existence. Most popular among these protocols are 1. RIP v1 and v2, OSPF, EIGRP, and BGP. Routing protocols should not be confused with routed protocols such as TCP and UDP. Routed protocols typically carry user data, whereas routing protocols provide the route information for user data packets. For most part, routing protocols are transparent to the end user. Routing protocols may be classified as below:

  • Distance Vector: Distance vector routing determines the direction and distance to any link in the internetwork. Smaller the metric, better the path. Distance vector routing is useful for smaller networks. Ex: RIP and IGRP.

  • Link State: Also known as SPF algorithms, SPF generates the exact topology of the entire network for route computation by listening to the first hand information. Bandwidth and delay are the most widely used metrics. Ex: OSPF and NLSP.

  • Balanced Hybrid: Balanced Hybrid combines some aspects of Link State and Distance Vector routing protocols. It uses distance vectors with more accurate metrics to determine the best paths to destination networks. Ex: EIGRP

   Routing protocols may also be classified as IGP and EGP routing protocols.

IGP(Interiror Gateway Protocols)

  • Handles routing in one domain (Automonus system) that is they send routing information between routers on the same internal network.

  • These fall in two categories : Distance Vector Protocol and Link State Protocol

  • RIP, OSPF are examples of IGP.

EGP(Exterior Gateway Protocols)

  • Handles routing outside Autonomous network it takes you from your network through ISP on to another network.

  • BGP is an examples of EGP protocol.

   Static And Dynamic Routing

Static Routing

1. location of the remote resource is specified at design time

2. administrator constructs the routing table in every router by putting in the entries for every network that could be a destination.

3. Static routes to network destinations are unchangeable.

Dynamic routing

1. location of the remote resource is decided at run time.

2. Routing protocol operating on the router is responsible for the creation, maintenance and updating of the dynamic routing table.

3. enables routers to select paths according to real-time logical network layout changes.

   Routing metrics

It is unit calculated by a routing algorithm for selecting or rejecting a routing path for transferring data/traffic.

  • Hop count: It is the number of nodes between starting node and destination node.

  • MTU(Maximum Transmission Unit): It is size of largest protocol data unit that can be transmitted. It is measured in bytes and is associated with a communications interface

  • Latency: It refers to several kinds of delays that come in network transmission

  • Costs

  • Bandwidth

   EIGRP (Enhanced Interior Gateway Protocol, a Cisco proprietary protocol)

Important terms used in EIGRP

  • Successor: A route (or routes) selected as the primary route(s) used to transport packets to reach destination. Note that successor entries are kept in the routing table of the router.

  • Feasible successor: A route (or routes) selected as backup route(s) used to transport packets to reach destination. Note that feasible successor entries are kept in the topology table of a router.

  • DUAL (Diffusing Update Algorithm): Enhanced IGRP uses DUAL algorithm to calculate the best route to a destination

  • For IGRP routing, you need to provide AS (Autonomous System) number in the command. Routers need AS number to exchange routing information. Routers belonging to same AS exchange routing information.

   OSPF(Open Shortest Path First) Routing Protocol:

  • OSPF is a link state technology that uses Dijkstra algorithm to compute routing information.

  • An OSPF area is a collection of networks and routers that have the same area identification.OSPF process identifier is locally significant.

   OSPF Area Types

  • Backbone Area (Area 0) - The backbone area is the central area to which all other areas in OSPF connect.

  • Standard Area : Default OSPF area type -Standard areas are defined as areas that can accept intra-area, inter-area and external routes. Intra-area routes refer to updates that are passed within the area. Inter-area routes refer to updates that are passed between areas. External routes refer to updates passed from another routing protocol into the OSPF domain by the Autonomous System Border Router (ASBR).

  • Stub Area : These areas do not accept routes belonging to external autonomous systems (AS); however, these areas have inter-area and intra-area routes. In order to reach the outside networks, the routers in the stub area use a default route which is injected into the area by the Area Border Router (ABR). A stub area is typically configured in situations where the branch office need not know about all the routes to every other office, instead it could use a default route to the central office and get to other places from there. Hence the memory requirements of the leaf node routers is reduced, and so is the size of the OSPF database.

  • Totally Stubby Area : These areas do not allow routes other than intra-area and the default routes to be propagated within the area. The ABR injects a default route into the area and all the routers belonging to this area use the default route to send any traffic outside the area.

  • Not So Stubby Area (NSSA) : This type of area allows the flexibility of importing a few external routes into the area while still trying to retain the stub characteristic.

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