1. Routing Protocols
Lecture # 6
Obaid Khan

2. Routed Protocol Definition
Routed Protocol – used to transmit user data (packets) through an internetwork. Routed protocols are assigned to an interface and determine the method of packet delivery.
Examples: IP, IPX, AppleTalk, DECNet, Banyan Vines, SNMP.

3. Routing Protocol Definition:
Defines Logical Addressing.
Routing protocol – any protocol that defines algorithms to be used for updating routing tables between routers. Basically, a routing protocol determines the path of a packet through an internetwork.
Examples: RIP, RIPv2, IGRP, EIGRP, OSPF, IS-IS, BGP

4. Approaches to Routing Distance Vector Routing protocol.
Link State Routing Protocol.

5. Distance-vector
Also known as Distributed Bellman-Ford or RIP (Routing Information Protocol)
Each node (router or host) exchange information with neighboring nodes
Neighbors are both directly connected to same network
Node maintains vector of link costs for each directly attached network and distance and next-hop vectors for each destination
Requires transmission of lots of information by each router
Distance vector to all neighbors
Contains estimated path cost to all networks in configuration
Changes take long time to propagate

6. Distance Vector Algorithms (1)
Dest
Next
Metric B 2 1 D A C D B
Dest
Next
Metric 1 C 2 D 3 A
Dest
Next
Metric C 3 B 2 1 B A
Dest
Next
Metric 1 C D 2

7. Distance Vector Algorithms (2)
Node A will learn of Node C’s shorter path to Node D and update its routing table A
Dest
Next
Metric 1 B D A C D B
Dest
Next
Metric 1 C D 2 B

8. Link-State Algorithms
Used Dijkstra’s Algorithm for shortest path.
Each node shares its link information so that all nodes can build a map of the full network topology
Link information is updated when a link changes state (goes up or down)
Link state determined by sending small “hello” packets to neighbors
Given full topology information, a node can determine the next best hop or a route from the source

9. Link-State Algorithms (1)
A-B
Link
B-C
C-D
A-B
Link
B-C
C-D
A-B
Link
B-C
C-D A C D
Assuming the topology is stable for a sufficiently long period, all nodes will have the same topology information B
A-B
Link
B-C
C-D

10. Link-State Algorithms (2)
A-B
Link
B-C
C-D
A-C
A-B
Link
B-C
C-D
A-C
A-C
A-C
A-B
Link
B-C
C-D
A-C A C D
A-C B
A-B
Link
B-C
C-D
A-C
Nodes A and C propagate the existence of link A-C to their neighbors and, eventually, to the entire network

11. Comparison of Distance Vector & Link State Routing Protocols
• Entire routing table is sent as an update • Distance vector protocol send periodic update at every 30 or 90 second • Update are broadcasted • Updates are sent to directly connected neighbor only • Routers don't have end to end visibility of entire network.
•Routing Loops.
Link state
• Updates are incremental & entire routing table is not sent as update • Updates are triggered not periodic • Updates are multicast • Update are sent to entire network & to just directly connected neighbor • Routers have visibility of entire network. • No routing loops • Convergence is fast because of triggered updates.

12. Static Routing Typically used in hosts
Enter subnet mask, router (gateway), IP address
Perfect for cases with few connections, doesn’t change much
E.g. host with a single router connecting to the rest of the Internet
Internet R1
IP: H1 H2 H3
For H1
Next Hop:

13. Dynamic Routing Most routers use dynamic routing
Automatically build the routing tables
As we saw previously, there are two major approaches
Link State Algorithms
Distance Vector Algorithms
First some terminology
AS = Autonomous System
Contiguous set of networks under one administrative authority
Common routing protocol
A connected network
There is at least one route between any pair of nodes

14. Application of IRP and ERP

15. Intra-AS Routing
Also known as Interior Router Protocols (IRP) or Interior Gateway Protocols (IGP)
Most common:
RIP: Routing Information Protocol
OSPF: Open Shortest Path First
IGRP: Interior Gateway Routing Protocol (Cisco proprietary)

16. Shortest Path Algorithm
Dijkstra’s Algorithm
Shortest Path Algorithm
Weighted Graphs

17. Shortest Path Algorithm Negative Weighted Graphs
Bellman-Ford’s Algorithm
Shortest Path Algorithm
Negative Weighted Graphs 6 7 s z y 8 -3 2 9 -2 x t -4 5 5 s z y 6 7 8 -3 2 9 -2 x t -4 6 7 s z y 8 -3 2 9 -2 x t -4 5 6 4 7 2 s z y 8 -3 9 -2 x t -4 5

18. ………….Bellman-Ford’s Algorithm6 4 7 2 s z y 8 -3 9 -2 x t -4 5 2 4 7 s z y 6 8 -3 9 -2 x t -4 5 2 4 7 s z y 6 8 -3 9 -2 x t -4 5 2 4 7 -2 s z y 6 8 -3 9 x t -4

19. Types Of Routing Protocol
Reactive (On-demand) protocols
Discover routes when needed
Source-initiated route discovery
Example: Ad-hoc on demand distance vector (AODV), Dynamic Source Routing (DSR).
Proactive protocols (Table Driven)
Traditional distributed shortest-path protocols
Based on periodic updates. High routing overhead
Example : Highly Dynamic Destination-Sequenced Distance Vector routing protocol (DSDV), Optimized Link State Routing Protocol (OLSR), Open Shortest path first (OSPF), RIP.

20. Routing Types Nodes must determine how to forward packets
Source routing
Routing decision is made at the sender.
In source routing complete route information from source to destination is included in the data packets .
Not feasible to the large scale network Hop-by-hop routing: Routing decision is made at each intermediate node.
Hop-by-hop Routing:
In hop-by-hop routing each data packet contains next hop address and destination address.
Routing decision is made at each intermediate node.

21. Proactive Routing Protocol
Table driven routing protocol

22. RIP ( Routing Information Protocol)
Distance vector algorithm
Proactive Routing Protocol
Distance vectors: exchanged every 30 sec via Response Message (also called advertisement)
Each advertisement: route to up to 25 destination nets

23. RIP (Routing Information Protocol)z w x y A D B C
Destination Network Next Router Num. of hops to dest.
w A 2
y B 2
z B 7 x
…. …
Routing table in D

24. RIP: Link Failure and Recovery
If no advertisement heard after 180 sec  neighbor/link declared dead
routes via neighbor invalidated
new advertisements sent to neighbors
neighbors in turn send out new advertisements (if tables changed)
link failure info quickly propagates to entire net

25. OSPF (Open Shortest Path First)
Uses Link State algorithm
LS packet dissemination
Topology map at each node
Route computation using Dijkstra’s algorithm
OSPF advertisement carries one entry per neighbor router
Advertisements disseminated to entire AS (via flooding)
Conceived as a successor to RIP

26. Destination Sequence Distance Vector Routing (DSDV)
DSDV is Proactive (Table Driven)
DSDV is Destination Based
Each node maintains routing information for all known destinations
Routing information must be updated periodically
Maintains routes which are never used
Traffic overhead even if there is no change in network topology

27. DSDV FUNCTIONALITY Route Advertisements Route Selection
Advertise to each neighbor own routing information which consist of :
Destination Address
Metric = Number of Hops to Destination
Destination Sequence Number
Rules to set sequence number information
On each advertisement increase own destination sequence number
If a node is no more reachable (timeout) increase sequence number of this node by 1 and set metric = 
Route Selection
Update information is compared to own routing table
Select route with higher destination sequence number (This ensure to use always newest information from destination)
Select the route with better metric when sequence numbers are equal.
Respond to Topology Changes
Immediate advertisements
Information on new Routes, broken Links, metric change is immediately propagated to neighbors.
Full/Incremental Update:
Full Update: Send all routing information from own table.
Incremental Update: Send only entries that have changed. (Make it fit into one single packet)

28. DSDV (Tables) A B C 1 2 Dest. Next Metric Seq A A-550 B 1 B-100 C 3
A-550 B 1
B-100 C 3
C-586
Dest.
Next
Metric
Seq A 1
A-550 B
B-100 C 2
C-588
Dest.
Next
Metric
Seq. A B 1
A-550 2
B-100 C
C-588

29. DSDV (Route Advertisement)
B increases Seq.Nr from 100 -> 102
B broadcasts routing information to Neighbors A, C including destination sequence numbers
(A, 1, A-500)
(B, 0, B-102)
(C, 1, C-588)
(A, 1, A-500)
(B, 0, B-102)
(C, 1, C-588) 1 1 A B C
Dest.
Next
Metric
Seq A
A-550 B 1
B-102 C 2
C-588
Dest.
Next
Metric
Seq A 1
A-550 B
B-102 C
C-588
Dest.
Next
Metric
Seq. A B 2
A-550 1
B-102 C
C-588

30. DSDV (New Node)
2. Insert entry for D with sequence number D-000 Then immediately broadcast own table
1. D broadcast for first time Send Sequence number D-000
(D, 0, D-000) A B C D
Dest.
Next
Metric
Seq. A
A-550 B 1
B-104 C 2
C-590
Dest.
Next
Metric
Seq. A 1
A-550 B
B-104 C
C-590
Dest.
Next
Metric
Seq. A B 2
A-550 1
B-104 C
C-590 D
D-000

31. DSDV (New Node cont.) A B C D
3. C increases its sequence number to C-592 then broadcasts its new table.
4. B gets this new information and updates its table…….
(A, 2, A-550)
(B, 1, B-102)
(C, 0, C-592)
(D, 1, D-000)
(A, 2, A-550)
(B, 1, B-102)
(C, 0, C-592)
(D, 1, D-000)
……… A B C D
Dest.
Next
Metric
Seq. A
A-550 B 1
B-104 C 2
C-590
Dest.
Next
Metric
Seq. A 1
A-550 B
B-102 C
C-592 D 2
D-000
Dest.
Next
Metric
Seq. A B 2
A-550 1
B-102 C
C-592 D
D-000

32. DSDV (no loops, no count to infinity)
2. B does its broadcast -> no affect on C (C knows that B has stale information because C has higher seq. number for destination D) -> no loop -> no count to infinity
1. Node C detects broken Link: -> Increase Seq. Nr. by 1 (only case where not the destination sets the sequence number -> odd number)
(D, 2, D-100)
(D, 2, D-100) D A B C
Dest.
Next
Metric
Seq. … D B 3
D-100
Dest.c
Next
Metric
Seq. … D C 2
D-100
Dest.
Next
Metric
Seq. … D 
D-101

33. DSDV (Immediate Advertisement)
3. Immediate propagation B to A: (update information has higher Seq. Nr. -> replace table entry)
2. Immediate propagation C to B: (update information has higher Seq. Nr. -> replace table entry)
1. Node C detects broken Link: -> Increase Seq. Nr. by 1 (only case where not the destination sets the sequence number -> odd number)
(D, , D-101)
(D, , D-101) D A B C
Dest.
Next
Metric
Seq. …
... D B 3
D-100 
D-101
Dest.
Next
Metric
Seq. … D B 4
D-100
Dest.c
Next
Metric
Seq. …
... D C 2
D-100 
D-101
Dest.c
Next
Metric
Seq. … D C 3
D-100
Dest.
Next
Metric
Seq. … D B 1
D-100
Dest.
Next
Metric
Seq. … D 1
D-100 
D-101

34. Reactive Routing Protocol
On-Demand routing protocol

35. AODV Concepts (1)
AODV: Ad hoc On-demand Distance Vector routing protocol
Pure on-demand routing protocol
A node does not perform route discovery or maintenance until it needs a route to another node or it offers its services as an intermediate node
Nodes that are not on active paths do not maintain routing information and do not participate in routing table exchanges
Uses a broadcast route discovery mechanism
Uses hop-by-hop routing
Routes are based on dynamic table entries maintained at intermediate nodes
Similar to Dynamic Source Routing (DSR), but DSR uses source routing

36. AODV Concepts (2)
Local HELLO messages are used to determine local connectivity
Can reduce response time to routing requests
Can trigger updates when necessary
Sequence numbers are assigned to routes and routing table entries
Used to maintain freshness of route
Every node maintains two counters
Node sequence number
Broadcast ID

37. AODV Route Request (1)
Initiated when a node wants to communicate with another node, but does not have a route to that node
Source node broadcasts a route request (RREQ) packet to its neighbors
broadcast_id
dest_addr
type
flags
hopcnt
resvd
dest_sequence_#
source_addr
source_sequence_#

38. AODV Route Request (2) Sequence numbers
Source sequence indicates “freshness” of reverse route to the source
Destination sequence number indicates freshness of route to the destination
Every neighbor receives the RREQ and either …
Returns a route reply (RREP) packet, or
Forwards the RREQ to its neighbors
(source_addr, broadcast_id) uniquely identifies the RREQ
broadcast_id is incremented for every RREQ packet sent
Receivers can identify and discard duplicate RREQ packets

39. AODV Route Request (3) If a node cannot respond to the RREQ
The node increments the hop count
The node saves information to implement a reverse path set up (AODV assumes symmetrical links)
Neighbor that sent this RREQ packet
Destination IP address
Source IP address
Broadcast ID
Source node’s sequence number
Expiration time for reverse path entry (to enable garbage collection)

40. AODV Example (1) Node 1 needs to send a data packet to Node 74 6 1 7 5 3 2
Node 1 needs to send a data packet to Node 7
Assume Node 6 knows a current route to Node 7
Assume that no other route information exists in the network (related to Node 7)

41. AODV Example (2) Node 1 sends a RREQ packet to its neighbors4 6 1 7 5 3 2
Node 1 sends a RREQ packet to its neighbors
source_addr = 1
dest_addr = 7
broadcast_id = broadcast_id + 1
source_sequence_# = source_sequence_# + 1
dest_sequence_# = last dest_sequence_# for Node 7

42. AODV Example (3) 4 6 1 7 5 3 2
Nodes 2 and 4 verify that this is a new RREQ and that the source_sequence_# is not stale with respect to the reverse route to Node 1
Nodes 2 and 4 forward the RREQ
Update source_sequence_# for Node 1
Increment hop_cnt in the RREQ packet

43. AODV Example (4) RREQ reaches Node 6, which knows a route to 71 7 5 3 2
RREQ reaches Node 6, which knows a route to 7
Node 6 must verify that the destination sequence number is less than or equal to the destination sequence number it has recorded for Node 7
Nodes 3 and 5 will forward the RREQ packet, but the receivers recognize the packets as duplicates

44. AODV Route Reply (1)
If a node receives an RREQ packet and it has a current route to the target destination, then it unicasts a route reply packet (RREP) to the neighbor that sent the RREQ packet
dest_addr
type
flags
hopcnt
rsvd
dest_sequence_#
source_addr
lifetime
prsz

45. AODV Route Reply (2)
Intermediate nodes propagate the first RREP for the source towards the source using cached reverse route entries
Other RREP packets are discarded unless…
dest_sequence_# number is higher than the previous, or
destination_sequence_# is the same, but hop_cnt is smaller (i.e., there’s a better path)
RREP eventually makes it to the source, which can use the neighbor sending the RREP as its next hop for sending to the destination
Cached reverse routes will timeout in nodes not seeing a RREP packet

46. AODV Example (5) 4 6 1 7 5 3 2
Node 6 knows a route to Node 7 and sends an RREP to Node 4
source_addr = 1
dest_addr = 7
dest_sequence_# = maximum(own sequence number, dest_sequence_# in RREQ)
hop_cnt = 1

47. AODV Example (6) 4 6 1 7 5 3 2
Node 4 verifies that this is a new route reply (the case here) or one that has a lower hop count and, if so, propagates the RREP packet to Node 1
Increments hop_cnt in the RREP packet

48. AODV Example (7) 4
Dest
Next
Hops 7 4 3 6 1 7 5 3 2
Node 1 now has a route to Node 7 in three hops and can use it immediately to send data packets
Note that the first data packet that prompted path discovery has been delayed until the first RREP was returned

49. AODV Route Maintenance
Route changes can be detected by…
Failure of periodic HELLO packets
Failure or disconnect indication from the link level
Failure of transmission of a packet to the next hop (can detect by listening for the retransmission if it is not the final destination)
The upstream (toward the source) node detecting a failure propagates an route error (RERR) packet with a new destination sequence number and a hop count of infinity (unreachable)
The source (or another node on the path) can rebuild a path by sending a RREQ packet

50. AODV Example (8) Assume that Node 7 moves and link 6-7 breaks4 6 1 7 5 3 2 7
Assume that Node 7 moves and link 6-7 breaks
Node 6 issues an RERR packet indicating the broken path
The RERR propagates back to Node 1
Node 1 can discover a new route

51. Dynamic Source Routing (DSR)

52. Hierarchical Algorithms (1)
Scalability – MANET protocols often do not perform well for large networks (especially if not dense)
Global topology is based on the connectivity of each mobile node
Clusters can be used to provide scalability
Clusters are formed (dynamically, of course) to provide hierarchy
Global routing is done to clusters
Local routing is done to nodes within a cluster
Clusters of clusters (super-clusters) can be formed to extend hierarchy
Similar in principle to IP subnets

53. Hierarchical Algorithms (2)
A special node, called the cluster-head, is designated in each cluster
Responsible for routing data to or from other clusters
May be a special node, or may be designated through a clustering algorithm
Algorithms
Clustering -- form clusters
Cluster-head identification -- may be an integral part of the clustering algorithm
Routing -- some routing algorithm is still needed
Applied at each level of the hierarchy

54. Hierarchical Algorithm Example
Cluster 2
Cluster 1
Cluster 3