CCNP 1 v3.0 Module 3 Routing Overview

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CCNP 1 v3.0 Module 3Routing Overview

Cisco Networking Academy


Objectives

• Routing – Static and Dynamic

• Default Routing

• Floating Static Routes

• Convergence

• Route Calculation


Routing Fundamentals


Static Routing

• Static routing is useful in networks that have a single path to any destination network.

• Static routing reduces the memory and processing burdens on a router.

• To configure static routing on a Cisco router, use the ip route command. This command uses the following syntax:

Router(config)#ip route destination-prefix destination-prefix-mask {address | interface} [distance] [tag tag] [permanent]


Dynamic Routing

There are several different methods of classifying routing protocols:

1. Interior vs. Exterior

2. Distance Vector vs. Link-state

3. Classful vs. Classless


Configuring Dynamic Routing

• Dynamic routing of TCP/IP can be implemented using one or more protocols which are often grouped according to where they are used.

• Routing protocols designed to work inside an autonomous system are categorized as interior gateway protocols (IGPs). – RIP, IGRP, EIGRP, OSPF

• Protocols that work between autonomous systems are classified as exterior gateway protocols (EGPs). – BGP, ISIS

• Protocols can be further categorized as either distance vector or link-state routing protocols, depending on their method of operation.


Distance Vector Routing Protocols

• Routing protocols may be classified as either distance vector or link-state routing protocols.

These classifications describe the algorithm, or formula, that routers use to calculate and exchange routing information.

Distance vector routing protocols are based on the Bellman-Ford algorithm.

Distance vector routing protocols are concerned with the distance and vector, or direction, of destination networks (the exiting interface).

Distance (metric) is the proximity to the destination network which is calculated as either hop-count or bandwidth.


Distance Vector Routing Protocols

• Simple distance vector routing protocols offer two primary advantages over link-state protocols. 1. Relatively easy to configure.

2. Generally use less memory and processing power.


Link-state Routing Protocols

• Offer greater scalability and faster convergence than distance vector protocols.

• Require more memory and processing power from the router.

• Based on Dijkstra’s algorithm (OSPF).

• Builds a complete database of all the link states of every router in its area.

• Benefits include faster convergence and improved bandwidth utilization over distance vector protocols.

• May overtax low-end hardware.

• Require more complex administration.


Hybrid Routing Protocol: EIGRP

• EIGRP is considered a hybrid routing protocol because it has characteristics of both distance-vector and link-state routing protocols.

• Some of the advantages of EIGRP are:

Rapid convergence

Event-driven updates

Loop-free routing

Multiprotocol support (IPv4, IPv6, IPX)


Default Routing

• Default routing sends packets to a configured next-hop address (or exiting interface) if the destination network address is not in the routing table.

• Default routes can be configured statically or learned dynamically through a routing protocol (redistributed into the routing protocol).

Router(config-router)# redistribute static

Or

Router(config-router)# default-information originate


Default Routing Overview

200.100.50.1


Configuring Static Default Routes


Default Routing with IGRP

To configure default routing for IGRP, use the global configurationcommand, ‘ip default-network [network number]’ at the border router.

RTB(config)#ip defaut-network 207.21.20.0


Floating Static Routes

• Floating static routes are static routes that are configured with a higher administrative distance then the routing protocol being used on the router.

• Floating static routes are used as a backup route to a route that is already known by the router through a routing protocol.

• The floating static route will not show up in the routing table until the same route known by the routing protocol goes down.


Administrative Distances


Configuring Floating Static Routes

Learned via RIPBackup Route


Convergence Issues

• Factors affecting the convergence time include the following:

Routing protocol used

Distance of the router, or the number of hops from the point of change

Number of routers in the network that use dynamic routing protocols

Bandwidth and traffic load on communications links

Load on the router

Traffic patterns in relation to the topology change


The Initiation of Routing Updates

• Routing protocols can instruct a router to update neighbors after a specific amount of time has passed, after a certain event has occurred, or both.

• Time-driven routing protocols wait for the update timer to expire and then send an update.

Periodic updates

• Protocols that are event-driven do not require the router to update neighbors until the router detects a change in the network topology.

Triggered updates or incremental updates

• Routing protocols that are exclusively time-driven react poorly to topology changes.

• Routing protocols that are exclusively event-driven could go for extended periods of time without sending updates.


Routing Metrics

• A routing metric is a value that measures distance to a destination network.

• Some routing protocols use only one factor to calculate a metric while others base their metric on two or more factors, including hop count, bandwidth, delay, load, reliability, and maximum transmission unit (MTU) – these are called composite metrics

• The more factors that make up a metric, the greater the ability is to adapt network operation to meet specific needs.


Summary

CCNP 1 v3.0 Module 3 Routing Overview

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