CCNA 2 v3.1 Module 6

Module 6 Routing & Routed Protocols CCNA 2 Module 6 Routing & Routed Protocols

Introducing Routing Routers must learn the direction to remote networks in order to forward packets. There are 2 ways to learn this information: Dynamic Routing Static Routing Routers use the routing process to Forward packets toward the destination network Decisions based upon the destination IP address Dynamic routing Routers learn information from other routers Scalable – each change learned from another router Static routing

Static Routing or next hop Configured manually by the network administrator Add and remove static routes when topology changes Static Route Operations are divided into three parts: Network administrator configures the route Router installs the route in the routing table Packets are routed using the static route Command Router#config terminal Router(config)#ip route 172.16.1.0 255.255.255.0 s0 Router(config)#ip route destination subnet outgoing network mask interface or next hop

Static Routes using Outgoing Interface Specifies Outgoing Interface

Static Route Using Next Hop Specifies Next Hop

The Difference between the 2 options is Administrative distance Administrative distance assigned to the route Administrative distance Optional Measures the reliability of the route (0 – 255) The lower the number the more reliable the route Set to 1 for next hop Set to 0 for outgoing interface Routers choose the route with the lowest administrative distance

To set a static route that is not 1 or 0 Static routes ip route 192.21.121.0 255.255.255.0 192.21.122.1 130 Static routes Can be used as a backup if dynamic route fails Must have higher admin no. to dynamic route Try the interactive media lab CCNA 2 Module 6 Page 6.1.2 Try the interactive media lab CCNA 2 Module 6 Page 6.1.3

Configuring a Default Route Default routes Route packets with destinations that do not match any of the other routes in the routing table Often used for internet-bound traffic Non-directly connected networks Special form of a static route ip route 0.0.0.0 0.0.0.0 [next-hop-address or outgoing if] Example ip route 0.0.0.0 0.0.0.0 s0 Try the interactive media lab CCNA 2 Module 6 Page 6.1.4

Verifying static route configuration show running-config Views the active configuration in RAM to verify that the static route was entered correctly show ip route Make sure that the static route is present in the routing table Ping <ip address> check a connection Traceroute <ip address> Shows the path to the ip address Can be used to identify where the connection fails Try Interactive media labs CCNA 2 Module 6 Page 6.1.5

Dynamic Routing

Allow routers to share information with other routers regarding Routing Protocols Allow routers to share information with other routers regarding the networks it knows about its proximity to other routers Used to build and maintain a routing table Examples: Routing Information Protocol - RIP Interior Gateway Routing Protocol - IGRP Enhanced Interior Gateway Routing Protocol -EIGRP Open Shortest Path First - OSPF

Routed Protocol Directs user traffic Provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme Internet Protocol (IP) Internetwork Packet Exchange (IPX)

Autonomous Systems A collection of networks under a common administration – e.g., MBNA_Europe sharing a common routing strategy American Registry of Internet Numbers -ARIN Assigns an identifying number to each AS It is a 16 bit number IGRP and EIGRP have autonomous system numbers

Purpose of a routing protocol and autonomous systems Learns all available routes Places the best routes into the routing table Removes routes that are no longer valid Router use information in the routing table To forward routed protocol packet Routing protocols change/update routing tables When the network topology changes Internetwork is converged when All routers in an internetwork are operating with the same knowledge Fast convergence is desirable

Classes of routing protocols Distance vector Uses distance and direction Link-state Shortest path first Recreates the exact topology of the entire internetwork

Distance vector routing protocol features Router passes periodic copies of a routing table to directly connected router These updates communicate topology changes Updates do not allow router to know exact internetwork topology it only sees its neighbours routers Also called Bellman-Ford algorithms When a router receives an update where there is an information change It uses this information to alter the distance and update the routing table

Distance Vector Concept

Link-state routing protocol features Link-state algorithms are also known as Dijkstras algorithm or SPF (shortest path first) algorithms A link-state routing algorithm Maintains a complete database of the topology A full knowledge of distant routers and how they interconnect

Link State Routing use Link-state advertisements (LSAs) A small packet of routing information sent between routers Topological database A collection of information gathered from LSAs. SPF algorithm (shortest path first) A calculation performed on the database resulting in the SPF tree Routing tables A list of the known paths and interfaces

Link State Routing Protocol Features Network discovery processes for link state routing LSAs are exchanged between directly connected routers with information about directly connected networks These LSAs are accumulated on each router and a topological database is constructed The SPF algorithm uses this database to calculate shortest path It then builds a tree, with itself as the root, consisting of all possible paths to each network It sorts these paths Shortest Path First (SPF) Lists the best paths and ports to these destination networks in the routing table

To achieve convergence Each router keeps track of its neighbor routers Router, Name, Interface status, Cost of the link The first router to become aware of a topology change Forwards the information to all other routers Using a Link State Advertisement (LSA) When a router receives a LSA it It adds the information to the routers database and the SPF algorithm is run again Link-state concerns: Processor overhead Memory requirements Bandwidth Consumption

Path determination A router determines the path using: A path determination function A switching function Path determination Occurs at network layer Router uses the routing table to determine the best path Switching Router accepts a packet on one interface and forward it to a second interface on the same router Router encapsulates the packet in the appropriate frame type for the next data link

Routing Configuration To enable IP routing protocol on a router Setting global parameters and routing parameters Global tasks Selecting a routing protocol (RIP, IGRP, EIGRP or OSPF) Specify the network Routing metric Help routers find the best path to each network

<protocol> e.g., rip, igrp, ospf… Command Layout Router(config)#router <protocol> <option> Router(config-router)#network <network no> <protocol> e.g., rip, igrp, ospf… <option> e.g., autonomous system no <network no> directly connected network Commands Router(config)# router rip Router(config-router)#network 192.101.1.0 Try lab activity CCNA 2 Module 6 Page 6.3.2

Routing Protocols RIP – Distance vector interior routing protocol IGRP – Cisco's distance vector interior routing protocol OSPF – A link-state interior routing protocol EIGRP – Cisco’s advanced distance vector interior routing protocol BGP – A distance vector exterior routing protocol

Routing Information Protocol (RIP) Originally specified in RFC 1058 Interior gateway protocol Distance vector routing protocol Metric for path selection is hop count If hop count is greater than 15, packet discarded Routing updates broadcast every 30 seconds Interior Gateway Routing Protocol (IGRP) Proprietary protocol developed by Cisco Metrics used are Bandwidth, load, delay and reliability Routing updates broadcast every 90 seconds

Open Shortest Path First (OSPF) Nonproprietary CISCO protocol Link-state routing protocol Originally described in RFC 2328. Uses SPF algorithm to calculate the lowest cost to a destination Routing updates are flooded as topology changes occur

EIGRP - Enhanced Interior Gateway Routing Protocol Cisco proprietary protocol Enhanced distance vector routing protocol Uses load balancing Combination of distance vector and link-state Calculates shorted path first using Diffused Update Algorithm (DUAL) Routing updates Broadcast every 90 seconds or as triggered by topology changes

Border Gateway Protocol (BGP) Exterior Gateway Protocol Distance vector routing protocol Used between ISPs or ISPs and clients Used to route Internet traffic between autonomous systems Try Interactive Lab CCNA 2 Module 6 Page 6.3.3

Exterior Gateway Protocols EGP designed for use between two different networks that are under the control of different organizations, ISPs. In order for routing to begin you need: A list of neighbor routers with which to exchange routing information A list of networks to advertise as directly reachable The autonomous system number of the local router Try interactive lab CCNA 2 Module 6 Page 6.3.4

Distance vector (RIP or IGRP) Known as Bellman-Ford algorithm Routing decisions based upon information provided by its neighboring routers Inform neighbors of your routing table on periodic basis Advantages use few resources Disadvantages Slow convergence Metrics don’t scale well Decisions made based on Finding the distance (number of hops) and vector (direction) to any link on the internetwork

Link-state (OSPF or IS-IS) Shortest Path First algorithm Flood routing information to all routers Each router gets a complete view of internetwork Routing updates sent on topology change (LSA) They are event triggered Resulting in quick convergence Quick convergence Prevents routing loops Prevents routing errors Use more system resources Expensive to implement but scalable