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GATE CSE 2003 | Question: 27

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Which of the following assertions is FALSE about the Internet Protocol (IP)?

  1. It is possible for a computer to have multiple IP addresses
  2. IP packets from the same source to the same destination can take different routes in the network
  3. IP ensures that a packet is discarded if it is unable to reach its destination within a given number of hops
  4. The packet source cannot set the route of an outgoing packets; the route is determined only by the routing tables in the routers on the way

11 Answers

Best answer
60 60 votes

In computer networking, source routing, also called path addressing, allows a sender of a packet to partially or completely specify the route of the packet takes through the network. In contrast, in non-source routing protocols, routers in the network determine the path based on the packet's destination.

http://en.wikipedia.org/wiki/Source_routing

Answer is D.

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38 38 votes
The correct answer is Option D.

Let’s go option wise

Option A). Yes it is possible for the  computer to have multiple addresses, assumed that the computer using DHCP protocol so new IP addresses each time when its connected to network.

hence option A is True.

Option B). IP packets can take different path from same  source to same destination, as IP is connection less based protocol packet have authority to take different path to reach the destination.

hence option B is also True.

Option C).In IP header there is a field known as Time to Live field, this field is limit for packet which says that number of intermediate router can packets traverse, it’s value is decremented by 1 when it passes one intermediate router, and when this field reaches 0 then the packet has been discarded by the router.

But when this field becomes 0 when packets receiving at destination then it will not get discarded, it has been accepted by the destination.

hence IP ensures a packet is discarded if it is not reaching the destination within a given number of hops(Intermediate Router).

hence option C is also True.

Option D).

In IP header’s option field, there is an option known as Strict Source Routing(SSR) it tells the packet to follow the route that has mentioned in this field, means packet has to traverse those router which is mentioned in it , if packet reaches the destination and it has not been traversed all the router as mentioned in SSR field then that packet get discarded even it reaches the correct destination, and this field is set by Source only.

So , it is incorrect that packet source cannot route the packet.

hence option D is False.
9 9 votes

Option-D

  1. The packet source cannot set the route of an outgoing packets; the route is determined only by the routing tables in the routers on the way
  2. Bcz in strict source routing or lose source routing path is set by the source not by router and main task of router is to check outgoing path with the help of forwording table inside it.
3 3 votes

Option A: It is possible for a computer to have multiple IP addresses

This statement is true.  
A single host may possess multiple network interfaces (e.g., Ethernet, Wi-Fi, loopback, virtual interfaces), each with its own assigned IP address. Additionally, a single interface may be configured with multiple IP addresses through address aliasing. This is standard practice in servers, firewalls, and multi-homed systems.

 


 

Option B: IP packets from the same source to the same destination can take different routes in the network

This statement is true.  
IP is a connectionless, best-effort protocol. Each packet is routed independently by intermediate routers based on their current routing tables. Routing tables may change dynamically due to link failures, load balancing, or policy updates. As a result, packets belonging to the same flow may follow different paths through the network. This behavior is inherent to IP’s design and is not considered an error.

Option C: IP ensures that a packet is discarded if it is unable to reach its destination within a given number of hops

This statement is true.  
The IPv4 header includes an 8-bit Time-to-Live (TTL) field, which is decremented by one at each router. When the TTL reaches zero, the packet is discarded, and an ICMP Time Exceeded message may be generated. This mechanism prevents indefinite looping of packets in the network and ensures bounded delivery attempts. Thus, IP enforces a maximum hop limit.

Option D: The packet source cannot set the route of an outgoing packet; the route is determined only by the routing tables in the routers on the way

This statement is false.

While it is true that in normal operation, routing decisions are made solely by routers using their forwarding tables, the IP protocol does permit the source host to influence the path through the use of source routing options.

Specifically, IPv4 supports two source routing options:

  • Loose Source and Record Route (LSRR) specifies a list of intermediate routers the packet must pass through, with flexibility in intermediate hops.
  • Strict Source and Record Route (SSRR) requires the packet to pass through each specified router in exact sequence, with no intermediate routers allowed.

Although these options are rarely used in modern networks due to security concerns (e.g., route manipulation, spoofing), and are often filtered by firewalls, they remain part of the official IP specification.

Therefore, the assertion that “the packet source cannot set the route” is incorrect. The capability exists within the protocol, even if it is not commonly enabled.

http://web.cs.wpi.edu/~emmanuel/courses/cs513/S10/pdf_slides/network2.pdf

$$
\boxed{\text{D}}
$$

1 1 vote
  1. It is possible for a computer to have multiple IP addresses. True: A computer with multiple network interface cards, can have more than one IP.
  2. IP packets from the same source to the same destination can take different routes in the network. True: this is the characteristics of packet switching.
  3. IP ensures that a packet is discarded if it is unable to reach its destination within a given number of hops. True: If TTL expires packet will be discarded.
  4. The packet source cannot set the route of an outgoing packets; the route is determined only by the routing tables in the routers on the way. False: Using source routing a sender can specify the route of an outgoing packets.
0 0 votes
a. IP addressing

A host can have multiple IP addresses (multiple NICs, virtual interfaces, aliasing, multihoming). So statement (1) is conceptually correct.

b. Packet switching & route variability

IP is connectionless and routers forward each packet based on their routing tables. Routing decisions can change over time (or per-packet for load balancing), so packets from the same source to the same destination can take different routes. Statement (2) is correct.

c. TTL / Hop-limited forwarding

The IPv4 header includes a Time To Live (TTL) field (IPv6 calls it Hop Limit). Each router decrements TTL; when TTL reaches zero the router must discard the packet (it cannot forward it further). That behavior prevents infinite looping.

When a router discards a packet due to TTL expiry it normally sends an ICMP Time Exceeded message back to the sender — ICMP is the protocol used to report the discard. But the act of discarding when TTL hits zero is part of IP forwarding behavior (the router drops the packet). So the effect claimed in statement (3) — that a packet is discarded if it cannot reach the destination within a given number of hops — is indeed implemented (via TTL/Hop Limit).

d. Source routing

Source routing (an IP option in IPv4) allows the sender to partially or completely specify the path the packet should take (there are strict and loose variants). That means the source can influence or set the route — it’s not true that route is determined only by routers’ routing tables in all cases. So statement (4) (that the source cannot set the route and route is determined only by routers) is not always true.
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