1) Each router maintains a routing table containing the outgoing link and distance to reach each destination node. 2) Routers periodically share their routing tables with neighbors so each can update its own table. 3) This allows routers to continuously determine the shortest paths to all destinations as network conditions change.

1. MADE BY
MOHIT AGARWAL – 161080107026
SUBJECT – COMPUTER NETWORKS

2. • Each router maintains a routing table, where each node in the
network has an entry in the table.
• Each entry contains two parts, the outgoing line for the destination
(node) and the distance (time, cost) to the destination.
• Each router knows the distance to its neighbors.
• In a certain period of time, each router sends the table to each of its
neighbors.
• When a router receives a table from each of its neighbors, it updates
its routing table, determines the new minimum distance and the
outgoing link for the destination.

3. Routing table for A To cost via
A 0 -
B 12 B
C 25 B
D 40 B
E 14 E
F 23 E
G 18 B
H 17 J
I 21 E
J 9 J
K 24 J
L 29 J

4. A B C D E A B C D E
# # # # 1 2 3 4
1 # # # 3 2 3 4
1 2 # # 3 4 3 4
1 2 3 # 5 4 5 4
1 2 3 4 5 6 5 6
7 6 7 6
7 8 7 8
: : : :
Count to infinity problem shows that good news
propagates fast, bad news propagates slow.

5. In link state routing each node follows certain steps :
a) Discover its neighbors
b) Measure the cost to its neighbors
c) Broadcast a packet with this information to all other nodes
d) Compute the shortest paths to every other router

6. 1. Each router establishes a relationship with its neighbors
2.Each router generates Link State Advertisements (LSAs)
which are distributed to all routers
LSA = (link id, state of the link, cost, neighbors of the link)
3. Each router maintains a database of all received LSAs
(topological database or link state database), which describes
the network has a graph with weighted edges
4. Each router uses its link state database to run a shortest path
algorithm (Dijkstra's algorithm) to produce the shortest path
to each network

7. Received
LSAs
IP Routing
Table
Dijkstra’s
Algorithm
Link State
Database
LSAs are flooded
to other interfaces

8. DISTANCEVECTOR ROUTING LINK STATE ROUTING
It is used to calculate shortest cost path. It is used to calculate link state cost.
Sends message to their neighbors.
(As we see in count to infinity problem)
Sends message to every other node in the
network.
It is decentralized routing algorithm. It is centralized global routing algorithm.
Sends larger updates only to neighboring
routers.
Sends small updates everywhere.
Requires less CPU power and less memory
space.
Requires more CPU power and more
memory space.
Simple to implement and support. Expensive to implement and support.

9.  With distance vector routing, each node has
information only about the next hop:
 Node A:To reach F go to B
 Node B:To reach F go to D
 Node D:To reach F go to E
 Node E: Go directly to F
 Distance vector routing makes poor routing
decisions if directions are not completely
correct (e.g., because a node is down).
 If parts of the directions incorrect, the routing may
be incorrect until the routing algorithms has
re-converged.
A B C
D E F

10.  In link state routing, each node has a complete
map of the topology
 If a node fails, each node can calculate
the new route
 Difficulty:All nodes need to have a consistent
view of the network
A B C
D E F
A B C
D E F
A B C
D E F
A B C
D E F
A B C
D E F
A B C
D E F
A B C
D E F