RIP is a distance-vector routing protocol that uses hop count as its routing metric. It operates at the OSI application layer and uses port 520. The maximum number of hops in a RIP route is 15. There are three versions of RIP with RIP v2 being classless and supporting authentication. RIP timers include the update, invalid, hold down, and flush timers. OSPF is a link-state routing protocol that uses the SPF/Dijkstra algorithm to calculate the shortest path. It has five message types including hello, database description, link-state request, link-state update, and link-state acknowledgement messages.

1. RIP PROTOCOL

2. 1. What do you understand by Routing Information Protocol (RIP) in the
context of networking?
Answer:
The Routing Information Protocol (RIP) is a dynamic routing protocol that
finds the optimum path between the source and destination networks by using
hop count as a routing metric. It is a distance-vector routing protocol with an
AD value of 120 that operates at the OSI application layer. The RIP protocol uses
port 520. The number of routers between the source and destination networks
is referred to as the hop count. The path with the fewest hops is selected the
best route to a network and is entered into the routing table. The number of
hops allowed in a path between source and destination is limited by RIP, which
eliminates routing loops. The maximum number of hops allowed by RIP is 15,
and a hop count of 16 is considered unreachable by the network.

3. RIP versions :
There are three versions of routing information protocol – RIP Version1, RIP Version2,
and RIPng.
Features of RIP
1. Updates of the network are exchanged periodically.
2. Updates (routing information) are always broadcast.
3. Full routing tables are sent in updates.
4. Routers always trust routing information received from neighbor routers. This is also
known as Routing on rumors.
5. RIP v1 is known as Classful Routing Protocol because it doesn’t send information of
subnet mask in its routing update.
6. RIP v2 is known as Classless Routing Protocol because it sends information of subnet
mask in its routing update.

4. RIP v1 RIP v2 RIPng
Sends update as broadcast Sends update as multicast Sends update as multicast
Broadcast at
255.255.255.255
Multicast at 224.0.0.9
Multicast at FF02::9 (RIPng
can only run on IPv6
networks)
Doesn’t support
authentication of updated
messages
Supports authentication of
RIPv2 update messages
–
Classful routing protocol
Classless protocol updated
supports classful
Classless updates are sent

5. RIP timers:
Update timer: The default timing for routing information being exchanged by the routers
operating RIP is 30 seconds. Using an Update timer, the routers exchange their routing
table periodically.
Invalid timer: If no update comes until 180 seconds, then the destination router considers
it invalid. In this scenario, the destination router mark hop counts as 16 for that router.
Hold down timer: This is the time for which the router waits for a neighbor router to
respond. If the router isn’t able to respond within a given time then it is declared dead. It is
180 seconds by default.
Flush time: It is the time after which the entry of the route will be flushed if it doesn’t
respond within the flush time. It is 60 seconds by default. This timer starts after the route
has been declared invalid and after 60 seconds i.e time will be 180 + 60 = 240 seconds.
R1(config-router)# timers basic
R1(config-router)# timers basic 20 80 80 90

6. Difference between Border Gateway Protocol (BGP) and Routing
Information Protocol (RIP)
1. Border Gateway Protocol (BGP):
In BGP, Transmission Control Protocol is used. It is a type of mesh topology or design. It works by two
independent networks (Autonomous Systems or AS) exchanging routing information. The two routers agree to
exchange information about how to reach certain IP-ranges. BGP uses Transmission Control Protocol (TCP) port
179.
2. Routing Information Protocol (RIP):
RIP stands for Routing Information Protocol in which distance vector routing protocol is used for data/packet
transmission. In Routing Information Protocol (RIP), the maximum number of hops is 15, because it prevents
routing loops from source to destination. Mechanism like split horizon, route poisoning, and holdown are used to
prevent incorrect or wrong routing information. Sally Floyd and Van Jacobson [1994] suggested that, without slight
randomization of the timer, the timers are synchronized overtime. Compared to other routing protocols, RIP
(Routing Information Protocol) is poor and limited in size i.e. small network. The main advantage of using RIP is
that it uses the UDP (User Datagram Protocol).

7. Difference between Border Gateway Protocol (BGP) and Routing Information Protocol (RIP) :
S. No. Border Gateway Protocol Routing Information Protocol
1. BGP stands for Border Gateway Protocol. RIP Stands for Routing Information Protocol.
2. It initially came in the year 1989. It was defined in the year 1988.
3. It works on Best path algorithm. RIP works on Bellman Ford algorithm.
4.
It is basically used for very larger size organizations as
compared to RIP.
It is basically used for smaller size organizations.
5. It is an external gateway protocol. It is an industry standard dynamic routing protocol.
6. It is a more intelligent routing protocol than RIP. It is not a very intelligent dynamic routing protocol.
7. The networks are classified as areas and tables.
The networks are classified as areas, sub areas,
autonomous systems and backbone areas.
8. It calculates the metric in terms of Hop Count. It calculates the metric in terms of Bandwidth.
9. It is hybrid type. It is a Vector State type.
10. There is no such restriction on the hop count. It allows a maximum of 15 hops.
11. It has design type- Fully meshed. It has design type- Flat network.
12. It consumes more bandwidth for two purposes-
It consumes more bandwidth because of the sending
of whole routing table after every 90s (by default)

8. Difference between Distance vector routing and Link State
routing
Distance Vector Routing –
•It is a dynamic routing algorithm in which each router computes a distance between itself and each possible
destination i.e. its immediate neighbors.
•The router shares its knowledge about the whole network to its neighbors and accordingly updates the table
based on its neighbors.
•The sharing of information with the neighbors takes place at regular intervals.
•It makes use of Bellman-Ford Algorithm for making routing tables.
•Problems – Count to infinity problem which can be solved by splitting horizon.
– Good news spread fast and bad news spread slowly.
– Persistent looping problem i.e. loop will be there forever.
Link State Routing –
•It is a dynamic routing algorithm in which each router shares knowledge of its neighbors with every other router in
the network.
•A router sends its information about its neighbors only to all the routers through flooding.
•Information sharing takes place only whenever there is a change.
•It makes use of Dijkstra’s Algorithm for making routing tables.
•Problems – Heavy traffic due to flooding of packets.
– Flooding can result in infinite looping which can be solved by using the Time to live (TTL) field.

9. Comparison between Distance Vector Routing and Link State Routing:

10. Unicast Routing – Link State Routing
Unicast – Unicast means the transmission from a single sender to a single receiver. It is a
point-to-point communication between sender and receiver. There are various unicast
protocols such as TCP, HTTP, etc.
TCP is the most commonly used unicast protocol. It is a connection-oriented protocol that
relies on acknowledgement from the receiver side.
HTTP stands for HyperText Transfer Protocol. It is an object-oriented protocol for
communication.
There are three major protocols for unicast routing:
•Distance Vector Routing
•Link State Routing
•Path-Vector Routing

11. Link State Routing –
Link state routing is the second family of routing protocols. While distance-vector routers
use a distributed algorithm to compute their routing tables, link-state routing uses link-
state routers to exchange messages that allow each router to learn the entire network
topology. Based on this learned topology, each router is then able to compute its routing
table by using the shortest path computation.
Features of link state routing protocols –
•Link state packet – A small packet that contains routing information.
•Link state database – A collection of information gathered from the link-state packet.
•Shortest path first algorithm (Dijkstra algorithm) – A calculation performed on the database
results in the shortest path
•Routing table – A list of known paths and interfaces.

12. Calculation of shortest path –
To find the shortest path, each node needs to run the famous Dijkstra algorithm.
This famous algorithm uses the following steps:
Step-1: The node is taken and chosen as a root node of the tree, this creates the
tree with a single node, and now set the total cost of each node to some value
based on the information in Link State Database
Step-2: Now the node selects one node, among all the nodes not in the tree-like
structure, which is nearest to the root, and adds this to the tree. The shape of the
tree gets changed.
Step-3: After this node is added to the tree, the cost of all the nodes not in the tree
needs to be updated because the paths may have been changed.
Step-4: The node repeats Step 2. and Step 3. until all the nodes are added to the
tree

13. Link State protocols in comparison to Distance Vector protocols have:
1. It requires a large amount of memory.
2. Shortest path computations require many CPU circles.
3. If a network uses little bandwidth; it quickly reacts to topology changes
4. All items in the database must be sent to neighbors to form link-state packets.
5. All neighbors must be trusted in the topology.
6. Authentication mechanisms can be used to avoid undesired adjacency and problems.
7. No split horizon techniques are possible in the link-state routing.
•Open Shortest Path First (OSPF) is a unicast and intradomain routing protocol.
•It is an open-source protocol.
•OSPF is a classless routing protocol. Updates are multicasts at specific addresses (224.0.0.5 and 224.0.0.6).
•IP datagram that carries the messages from OSPF sets the value of the protocol field to 89
•OSPF is based on the SPF algorithm, which sometimes is referred to as the Dijkstra algorithm
•OSPF has two versions – version 1 and version 2. Version 2 is used mostly

14. Routing Loop
A routing loop is an issue that occurs when the routers forward
packets such that the same single packet ends up back at the same
router repeatedly in the network because of the unusual behavior of
the routing table when the data packets keep getting routed again
and again between two or more routers.
For example, it’s where traffic is being received from one connection
or one device (a router typically or a layer 3 switch) it sees traffic
coming from an interface and it sends this traffic to this host and
then that host receives the traffic and it sends this traffic to the
interface and it is receiving traffic from the host and it is sending it
right back to host so essentially the traffic goes in a loop.

15. How routing loops affect network performance?
If a routing loop exists then there is some problem in the routing table which is
called the poisoning of the routing table which can cause high damage to networks
like a failure of the network or slowness in the network as inaccurate data is being
added to the routing table and this causes abundance loss of data packets and the
waste of bandwidth.
If there are two hosts and the network trying to communicate or a big file is to be
transferred via this network and there’s a routing loop also. Due to the presence of
a routing loop every packet just keeps getting replicated so that it starts putting
load and strain on the network and at some point, a network outage can occur
because of these routing loops.

16. How to avoid Routing loops?
The following techniques are used to avoid Routing Loops.
1. Split Horizon
A split horizon is a technique to avoid routing loops by disabling the router from sending
information about a failed route in the routing table through the same interface that it
learned about the route from. This method includes Routing Information Protocol (RIP),
The virtual private LAN service (VPLS), and Enhanced Interior Gateway Routing Protocol
(EIGRP).
2. Hold-down Timers
It is a method that is used to prevent regular update messages from reinstating a route
that may have gone bad. Imagine a router receives an update from a neighbor indicating
that a previously accessible network is not working and is inaccessible then the hold-down
timer will start if a new update arrives from a neighbor with a better metric then hold
down is removed and data is passed otherwise it will ignore that new update.

18. OSPF PROTOCOL

19. OSPF Messages – OSPF is a very complex protocol. It uses five different
types of messages. These are as follows:
1. Hello message (Type 1) – It is used by the routers to introduce themselves to the other
routers.
2. Database description message (Type 2) – It is normally sent in response to the Hello
message.
3. Link-state request message (Type 3) – It is used by the routers that need information
about specific Link-State packets.
4. Link-state update message (Type 4) – It is the main OSPF message for building Link-State
Database.
5. Link-state acknowledgement message (Type 5) – It is used to create reliability in the
OSPF protocol.