GATE CSE 2017 | Set 2 | Question: 09

Question

Consider the following statements about the routing protocols. Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) in an $\textsf{IPv4}$ network.

1. RIP uses distance vector routing
2. RIP packets are sent using UDP
3. OSPF packets are sent using TCP
4. OSPF operation is based on link-state routing

Which of the above statements are CORRECT?

• A. I and IV only
• B. I, II and III only
• C. I, II and IV only
• D. II, III and IV only

Comments

The above is taken from kurose & Ross.

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Some Important Notes :

⇒ ICMP, IGMP, OSPF → protocols neither use TCP nor UDP as Transport layer protocol.

⇒RIP uses the UDP as its transport protocol with port no 520..

⇒ Unicast routing protocol => RIP, OSPF , BGP (Interdomain)

⇒ Multicast routing protocol => IGMP 

Why OSPF doesn't uses TCP and UDP ?

Reason : given in best answer

Answer 1

Statement $1$ is CORRECT because RIP is one of the Oldest DVR(Distance Vector Routing) Protocols which employ the hop count as a routing metric.

Statement $2$ is CORRECT because RIP uses the UDP as its transport protocol with port no $520.$

Statement $3$ is INCORRECT because OSPF doesnot use a transport protocol such as UDP or TCP but encapsulates its data directly into IP Packets.

Statement $4$ is CORRECT because OSPF is a routing protocol which uses Link State Routing(LSR) and works within a single Autonomous System.

PS: 

OSPF needs to perform reliable multicasting because it needs to talk to multiple possible neighbors on the same network segment. Now, TCP does not support multicast and UDP is not reliable Therefore, OSPF implements its own transport mechanism that allows both for reliability (acknowledgements and retransmissions of lost segments) and multicasting, bypassing both TCP and UDP.

Hence, Option C is CORRECT.

Comments

Link to more detailed explanation: Solved: OSPF and ICMP not use Transport protocol - Cisco Community

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Nice

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These 3 protocols neither use TCP nor UDP as Transport layer protocol,

1) ICMP

2) IGMP

3) OSPF

Answer 2

we all know RIP->Distance vector

and  OSPF->Link state routing

so 1 and 4 sure correct .

now agian RIP is used in UDP as in UDP 520 port

so 2 is also correct

so  1,2,4 correct

C is correct answer here

Answer 3

i)RIP uses distance vector routing, hence this is correct option .

ii)RIP is implemented as a process that uses the services of UDP on the well port number 520.so this is also correct.

iii)OSPF is implemented as a program in network layer,using service of the IP for propagation.but in option it is given TCP.hence wrong.

iv)OSPF is based on Link State Routing protocol.hence correct.

so answer is option C.

Comments

.this is what u meant OSPF runs directly on top of IP; it does not use TCP or User Datagram Protocol (UDP). OSPF performs its own error correction by means of checksums in its packet header and LSA

Answer 4

1. RIP uses distance vector routing (True)
2. RIP packets are sent using UDP(True)
3. OSPF packets are sent using TCP(False because it doesn't require TCP or UDP it directly added in IP Datagram)
4. OSPF operation is based on link-state routing(True).                    

Answer 5

COMMENT BELOW IF YOU HAVE ANY DOUBT

Comments

• RIP (Routing Information Protocol): Think of "Rest In Peace".
  • It’s old and slow (slow convergence).
  • It only cares about Distance (how many steps/hops to the grave).
  • UDP Connection: Imagine someone "Urgently Delivering Post" (UDP) to a graveyard.
• OSPF (Open Shortest Path First): Think of "OS" as "Overall Site".
  • It looks at the Link-State (the state of every "link" or road on the whole site).
  • It is Fast and complex.