Routing refers to the way routing tables are created to help in forwarding (Ref. FOROUZAN DCN). This slide describes the delivery,forwarding and routing of IP packets.

1. Routing Protocols:RIP, OSPF, and BGP
Amitava Nag
Assistant Professor
amitava.nag@aot.edu.in
April 11, 2012
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2. What is routing?
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3. What is routing?
Finding a path to a destination address
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4. What is routing?
Finding a path to a destination address
Routing is performed for many kinds of networks, including the
telephone network (Circuit switching) , electronic data networks (such
as the Internet).
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 2 / 23

5. What is routing?
Finding a path to a destination address
Routing is performed for many kinds of networks, including the
telephone network (Circuit switching) , electronic data networks (such
as the Internet).
In computer networking a Routing table, or Routing Information Base
(RIB), is a data structure in the form of a table-like object
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 2 / 23

6. What is routing?
Finding a path to a destination address
Routing is performed for many kinds of networks, including the
telephone network (Circuit switching) , electronic data networks (such
as the Internet).
In computer networking a Routing table, or Routing Information Base
(RIB), is a data structure in the form of a table-like object
A Routing table is stored either in a router or a networked computer
that lists the routes to particular network destinations.
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 2 / 23

7. What is routing?
Finding a path to a destination address
Routing is performed for many kinds of networks, including the
telephone network (Circuit switching) , electronic data networks (such
as the Internet).
In computer networking a Routing table, or Routing Information Base
(RIB), is a data structure in the form of a table-like object
A Routing table is stored either in a router or a networked computer
that lists the routes to particular network destinations.
The routing table contains information about the topology of the
network immediately around it.
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8. Common Fields Of Routing Table
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9. IP Routing Basics
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10. Static or Dynamic
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11. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
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12. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 5 / 23

13. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Fixes routes at boot time
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14. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Fixes routes at boot time
Useful only for simplest cases
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 5 / 23

15. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Fixes routes at boot time
Useful only for simplest cases
2 Dynamic Routing - A routing protocol is ”trying” to find the best way
to a given destination
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 5 / 23

16. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Fixes routes at boot time
Useful only for simplest cases
2 Dynamic Routing - A routing protocol is ”trying” to find the best way
to a given destination
entries are learned by routing protocols
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 5 / 23

17. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Fixes routes at boot time
Useful only for simplest cases
2 Dynamic Routing - A routing protocol is ”trying” to find the best way
to a given destination
entries are learned by routing protocols
Table initialized at boot time
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 5 / 23

18. Static or Dynamic
1 Static routing - YOU are defining the way packets are going
Entries are configured manually
Fixes routes at boot time
Useful only for simplest cases
2 Dynamic Routing - A routing protocol is ”trying” to find the best way
to a given destination
entries are learned by routing protocols
Table initialized at boot time
Necessary in large internets
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19. INTRA- AND INTERDOMAIN ROUTING
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20. INTRA- AND INTERDOMAIN ROUTING
An Autonomous system(AS) is a group of networks and routers under
the authority of a single administration.
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21. INTRA- AND INTERDOMAIN ROUTING
An Autonomous system(AS) is a group of networks and routers under
the authority of a single administration.
Routing inside an autonomous system is referred to as intradomain
routing.
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22. INTRA- AND INTERDOMAIN ROUTING
An Autonomous system(AS) is a group of networks and routers under
the authority of a single administration.
Routing inside an autonomous system is referred to as intradomain
routing.
Routing between autonomous systems is referred to as interdomain
routing.
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23. Autonomous systems
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24. Popular routing protocols
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25. Intradomain (Intra-AS) Routing
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26. Intradomain (Intra-AS) Routing
also known as Interior Gateway Protocols (IGP)
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27. Intradomain (Intra-AS) Routing
also known as Interior Gateway Protocols (IGP)
most common Intradomain routing protocols:
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28. Intradomain (Intra-AS) Routing
also known as Interior Gateway Protocols (IGP)
most common Intradomain routing protocols:
RIP: Routing Information Protocol
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29. Intradomain (Intra-AS) Routing
also known as Interior Gateway Protocols (IGP)
most common Intradomain routing protocols:
RIP: Routing Information Protocol
OSPF: Open Shortest Path First
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30. Intradomain (Intra-AS) Routing
also known as Interior Gateway Protocols (IGP)
most common Intradomain routing protocols:
RIP: Routing Information Protocol
OSPF: Open Shortest Path First
IGRP: Interior Gateway Routing Protocol (Cisco proprietary)
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31. DISTANCE VECTOR ROUTING
In distance vector routing,
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32. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

33. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

34. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
After powering-up each router only knows about directly attached
networks
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

35. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
After powering-up each router only knows about directly attached
networks
Routing table is sent periodically to all neighbour-routers
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

36. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
After powering-up each router only knows about directly attached
networks
Routing table is sent periodically to all neighbour-routers
Received updates are examined, changes are adopted in own routing
table
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

37. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
After powering-up each router only knows about directly attached
networks
Routing table is sent periodically to all neighbour-routers
Received updates are examined, changes are adopted in own routing
table
Metric information (originally) is number of hops
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

38. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
After powering-up each router only knows about directly attached
networks
Routing table is sent periodically to all neighbour-routers
Received updates are examined, changes are adopted in own routing
table
Metric information (originally) is number of hops
Use ”Bellman-Ford” algorithm
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 10 / 23

39. DISTANCE VECTOR ROUTING
In distance vector routing,
The least cost route between any two nodes(routers) is the route with
minimum distance.
Each router maintains a vector (table) of minimum distances to every
node
After powering-up each router only knows about directly attached
networks
Routing table is sent periodically to all neighbour-routers
Received updates are examined, changes are adopted in own routing
table
Metric information (originally) is number of hops
Use ”Bellman-Ford” algorithm
Examples: RIP, RIPv2, IGRP (Cisco)
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40. Initialization of tables in distance vector routing
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41. Updating in distance vector routing
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42. Distance vector routing tables
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43. Two-node instability
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44. Count to infinity
In this example we see what would happen if network link between router x
and router A crashes. Immediately, router A has no more information
about this net. What would happen if router B sends a routing update
now?
Now router A receives a routing update from router B including reach
ability information about router x. Because router A has no information
about router x, A adds this information in his routing table and continuous
sending his normal routing updates to router B, hereby increasing the hop
count by 1.
Either router A or router B has information about the router x, both
router will increase the hop count by 1 every routing update. Count to
infinity occurs. Now Update packets are caught in a routing loop.
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45. Example: Two-node instability
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46. Example: Two-node instability
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47. Split Horizon
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48. Split Horizon
A router will not send information about routes through an interface
over which the router has learned about those routes - Exactly THIS
is split horizon
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49. Split Horizon
A router will not send information about routes through an interface
over which the router has learned about those routes - Exactly THIS
is split horizon
Idea: ”Don’t tell neighbor of routes that you learned from this
neighbor”
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 18 / 23

50. Split Horizon
A router will not send information about routes through an interface
over which the router has learned about those routes - Exactly THIS
is split horizon
Idea: ”Don’t tell neighbor of routes that you learned from this
neighbor”
That’s what humans (almost) always do: Don’t tell me what I’ve told
you !
Amitava Nag (Academy of Technology) Routing Protocols April 11, 2012 18 / 23

51. Split Horizon
A router will not send information about routes through an interface
over which the router has learned about those routes - Exactly THIS
is split horizon
Idea: ”Don’t tell neighbor of routes that you learned from this
neighbor”
That’s what humans (almost) always do: Don’t tell me what I’ve told
you !
Cannot 100
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52. Split Horizon with Poison Reverse
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53. Split Horizon with Poison Reverse
Declare learned routes as unreachable
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54. Split Horizon with Poison Reverse
Declare learned routes as unreachable
”Bad news is better than no news at all”
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55. Split Horizon with Poison Reverse
Declare learned routes as unreachable
”Bad news is better than no news at all”
Stops potential loops due to corrupted routing updates
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56. Example: Split Horizon With Poison Reverse
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57. Link State Routing
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58. Link State Routing
Each node in the domain has the entire topology of the domain
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59. Link State Routing
Each node in the domain has the entire topology of the domain
the node can use Dijkstras algorithm to build a routing table
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60. Link State Routing
Each node in the domain has the entire topology of the domain
the node can use Dijkstras algorithm to build a routing table
link-state: each router exchanges information about its
neighborhood with all routers in the network when there is a change
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61. Concept of Link State Routing
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62. The End
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