1. CCNA 2 v3.1 Module 6

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

3. 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

4. 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 s0
Router(config)#ip route destination subnet outgoing
network mask interface or
next
hop

5. Static Routes using Outgoing Interface
Specifies
Outgoing
Interface

6. Static Route Using Next Hop
Specifies
Next Hop

7. 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

8. To set a static route that is not 1 or 0 Static routes
ip route
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

9. 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 [next-hop-address or outgoing if]
Example ip route s0
Try the interactive media lab CCNA 2 Module 6 Page 6.1.4

10. 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

11. Dynamic Routing

12. 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

13. 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)

14. 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

15. 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

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

17. 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

18. Distance Vector Concept

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. <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
Try lab activity CCNA 2 Module 6 Page 6.3.2

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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