IPv4 - Internet Protocol version 4

What is IPv4?

IPv4 stands for Internet Protocol version 4. It is the fourth version of the Internet Protocol and the most widely used protocol for identifying devices on a network using a 32-bit address. Each device on a network is assigned a unique IPv4 address to enable communication.

Why is IPv4 useful?

  • Identifying devices on a network

  • Routing data between devices across networks

  • Enabling internet communication

How it works?

  • Device gets an IP address – Either manually or via DHCP.

  • Data is sent with IP headers – Each packet includes source and destination IPv4 addresses.

  • Routers forward packets – Based on the destination IP, routers direct the packet toward its target.

  • Target device receives data – The device with the matching IP address processes the packet.

Where is IPv4 used?

  • Home networks – Routers assign IPv4 addresses to phones, laptops, TVs, etc.

  • Enterprise networks – Servers, workstations, and printers use IPv4 for communication.

  • Internet – Every website, server, and online service uses IPv4 (or IPv6) to identify and communicate with devices.

Which OSI Layer does IPv4 operate at?

  • IPv4 operates at the Network Layer (Layer 3) of the OSI model.

  • It handles logical addressing and routing between different networks.

  • It is responsible for packet forwarding, including routing through intermediate routers.

Topics in this section,

  • In this section, you are going to learn

  • Terminology

  • Version Info

Version & RFC Details

IPv4 Version

RFC Version

Year

Core Idea / Contribution

IPv4

RFC 760

1980

First formal specification of IPv4; defined datagram format and addressing.

RFC 791

1981

Replaces RFC 760; defines the modern IPv4 protocol including header structure, addressing, fragmentation.

RFC 792

1981

Defines ICMP for error and control messaging.

RFC 919

1984

Defines broadcasting methods in IP networks.

RFC 922

1984

Defines broadcasting methods in IP networks.

RFC 950

1985

Introduces subnetting for efficient IP address allocation.

RFC 1122

1989

Host requirements for Internet protocols including IPv4.

RFC 1812

1995

Router requirements for IPv4.

RFC 1918

1996

Defines private IP address ranges.

RFC 2131

1997

Defines DHCP for dynamic IP address assignment.

RFC 3021

2000

Allows /31 subnets for point-to-point links.

RFC 4632

2006

Classless Inter-Domain Routing (CIDR) notation and address allocation.

  • Setup

  • Setup

IPv4 Packet

S.No

Protocol Packets

Description

Size(bytes)

1

IPv4

42

Header

Version

IP version (4 for IPv4)

1

Header Length (IHL)

length of the IP header in 32-bit words.

1

Type of Service (ToS)

specifying the priority of the packet.

1

Total Length

total length of the IP packet (header + data).

2

Identification

uniquely identifying the packet fragments.

2

Flags

controlling or identifying fragments.

1

Fragment Offset

offset of a fragment

2

Time to Live (TTL)

maximum time the packet is allowed to remain

1

in the network.

Protocol

specifying the next level protocol (e.g., 6=TCP,17= UDP).

1

Header Checksum

error-checking the header.

2

Source IP Address

IP address of the sender.

4

Destination IP Address

IP address of the receiver.

4

Options

variable-length field for optional settings.

variable

Data(Payload)

actual payload carried by the IP packet.

variable(20)

IPv4 - Use Cases

S.no

Use Case

Description

1

Internet Communication

IPv4 is the foundational protocol for routing data across the internet using unique 32-bit addresses.

2

Enterprise Networking

Used in LANs and WANs for assigning IP addresses to devices like computers, printers, and servers.

3

Web Hosting & DNS

Websites are hosted on servers with IPv4 addresses; DNS maps domain names to these addresses.

4

Network Address Translation (NAT)

Enables multiple devices on a private network to share a single public IPv4 address.

5

VPN and Remote Access

IPv4 is used in tunneling protocols to securely connect remote users to private networks.

6

IoT Device Connectivity

Many IoT devices still rely on IPv4 for communication due to its widespread support.

7

DHCP Address Assignment

IPv4 works with DHCP to dynamically assign IP addresses to devices on a network.

8

VoIP and Streaming Services

IPv4 supports real-time data transmission for voice and video over IP networks.

IPv4 - Basic Features

S.no

Features

Description

1

Addressing

IPv4 uses 32-bit addresses, allowing for unique identification of devices on a network.

2

Header Structure

IPv4 packets have a structured header with fields like source/destination IP, TTL, protocol, etc.

3

Packet Routing

Routers use IPv4 addresses to forward packets across networks toward their destination.

4

Fragmentation

IPv4 supports fragmentation when packets exceed the MTU of a network segment.

5

Connectionless Protocol

IPv4 does not establish a connection before sending data; each packet is independent.

6

Subnetting

Allows division of IP networks into smaller subnetworks for efficient IP management.

7

NAT Compatibility

IPv4 works with Network Address Translation to conserve public IP addresses.

8

Broadcast Support

IPv4 supports broadcasting to all devices in a subnet.

9

Protocol Identification

The header includes a field to identify the encapsulated protocol.

10

TTL (Time to Live)

Limits the lifespan of a packet to prevent infinite looping in the network.

11

Classful Addressing (Legacy)

Originally, IPv4 used fixed address classes (A, B, C, D, E), though now replaced by CIDR.

Addressing - Testcases

Addressing - Test Cases

#

Test Case

Description

Expected Result

1

Assign Valid IPv4 Address

Assign 192.168.1.10

Address accepted

2

Assign Invalid IPv4 Address

Assign 999.999.999.999

Address rejected

3

Assign Broadcast Address

Assign 192.168.1.255

Used for broadcast only

4

Assign Network Address

Assign 192.168.1.0

Reserved for network ID

5

Assign Loopback Address

Assign 127.0.0.1

Used for local testing

6

Assign Link-Local Address

Assign 169.254.1.1

Used for auto-configuration

7

Assign Multicast Address

Assign 224.0.0.1

Used for multicast traffic

8

Assign Reserved Address

Assign 0.0.0.0

Used for default route

9

Assign Private Address

Assign 10.0.0.1

Used in private networks

10

Assign Public Address

Assign 8.8.8.8

Routable on the internet

11

Assign Address with Subnet Mask

Assign 192.168.1.10/24

Host identified within subnet

12

Assign Address with CIDR Notation

Assign 192.168.1.10/26

Host identified within smaller subnet

13

Assign Duplicate Address

Assign same IP to two hosts

IP conflict detected

14

Assign Address via DHCP

DHCP assigns IP

Address dynamically allocated

15

Assign Static IP Address

Manually assign IP

Address remains fixed

16

Assign Address via APIPA

No DHCP, APIPA assigns IP

Address in 169.254.x.x range

17

Assign Address via BOOTP

Legacy protocol assigns IP

Address allocated successfully

18

Assign Address via PPP

Point-to-point protocol assigns IP

Address assigned dynamically

19

Assign Address via VPN

VPN assigns IP

Address scoped to VPN

20

Assign Address via NAT

Internal IP mapped to public IP

Address translation occurs

21

Assign Address via Proxy

Proxy assigns IP

Address used for routing

22

Assign Address via IPv4 Header

IP set in packet header

Address used for routing

23

Assign Address with Invalid Subnet

Assign 192.168.1.10/33

Subnet mask rejected

24

Assign Address with Valid Subnet

Assign 192.168.1.10/30

Subnet accepted

25

Assign Address with Overlapping Subnet

Two subnets overlap

Routing conflict detected

26

Assign Address with Non-overlapping Subnet

Subnets are distinct

No conflict

27

Assign Address with Gateway

Assign IP with default gateway

Host can reach external networks

28

Assign Address without Gateway

No gateway assigned

Host limited to local subnet

29

Assign Address with DNS

DNS server assigned

Host can resolve domain names

30

Assign Address without DNS

No DNS assigned

Host cannot resolve domains

31

Assign Address with DHCP Lease Expiry

Lease expires

IP released or renewed

32

Assign Address with DHCP Reservation

IP reserved for MAC

Host always gets same IP

33

Assign Address with DHCP Conflict

Two hosts request same IP

Conflict resolved by server

34

Assign Address with DHCP Relay

Relay forwards request

IP assigned via remote server

35

Assign Address with DHCP Option 82

Relay agent info included

IP assigned based on location

36

Assign Address with ARP Resolution

IP resolved to MAC

Host reachable on LAN

37

Assign Address with ARP Conflict

Duplicate IP detected

ARP warning triggered

38

Assign Address with ICMP Echo

Ping IP address

Host responds if reachable

39

Assign Address with ICMP Unreachable

Ping unreachable IP

ICMP error returned

40

Assign Address with Routing Table Update

IP added to route table

Traffic routed correctly

41

Assign Address with Static Route

Route manually added

Traffic follows defined path

42

Assign Address with Dynamic Route

Route learned via protocol

Traffic routed dynamically

43

Assign Address with ACL

Access control list applied

Traffic filtered based on IP

44

Assign Address with Firewall Rule

IP allowed/blocked

Traffic permitted or denied

45

Assign Address with NAT Overload

Many IPs mapped to one

Port-based translation used

46

Assign Address with NAT Pool

IPs assigned from pool

Address allocated dynamically

47

Assign Address with IPsec Tunnel

IP used in secure tunnel

Traffic encrypted

48

Assign Address with QoS Policy

IP prioritized

Traffic shaped accordingly

49

Assign Address with SNMP Monitoring

IP monitored via SNMP

Status and usage tracked

50

Assign Address with Logging Enabled

IP assignment logged

Event recorded for audit

Header Structure - Testcases

Header Structure - Test Cases

#

Test Case

Description

Expected Result

1

Valid IPv4 Header

All fields correctly set

Packet accepted

2

Invalid Version Field

Version ? 4

Packet dropped

3

Valid IHL Field

IHL = 5 (20 bytes)

Header accepted

4

Invalid IHL Field

IHL < 5

Packet dropped

5

Valid Total Length

Length ? header + data

Packet accepted

6

Invalid Total Length

Length < header size

Packet dropped

7

Valid Identification Field

Unique ID set

Used for fragmentation

8

Duplicate Identification Field

Same ID reused

May cause reassembly issues

9

Valid Flags Field

DF or MF set correctly

Fragmentation behavior respected

10

Invalid Flags Field

Reserved bit set

Packet dropped or logged

11

Valid Fragment Offset

Offset aligned to 8 bytes

Packet accepted

12

Invalid Fragment Offset

Misaligned offset

Packet dropped

13

Valid TTL Field

TTL > 0

Packet forwarded

14

TTL = 0

TTL expired

ICMP Time Exceeded sent

15

TTL Decrement

TTL decremented by each router

Packet dropped if TTL = 0

16

Valid Protocol Field

Protocol = TCP/UDP/ICMP

Packet processed accordingly

17

Unknown Protocol Field

Unsupported protocol

Packet dropped

18

Valid Header Checksum

Correct checksum

Packet accepted

19

Invalid Header Checksum

Corrupted checksum

Packet dropped

20

Header Checksum Recalculation

After TTL decrement

Checksum updated

21

Valid Source IP Address

Proper IPv4 address

Packet accepted

22

Invalid Source IP Address

0.0.0.0 or broadcast

Packet dropped

23

Valid Destination IP Address

Proper IPv4 address

Packet routed

24

Invalid Destination IP Address

255.255.255.255

Packet broadcasted

25

Valid Options Field

Options present, IHL > 5

Packet accepted

26

Invalid Options Field

Malformed options

Packet dropped

27

No Options Field

IHL = 5

Standard header

28

Padding Present

Padding added to align header

Packet accepted

29

Padding Missing

Misaligned header

Packet dropped

30

Header Length Mismatch

IHL ? actual header size

Packet dropped

31

Header with Timestamp Option

Timestamp option set

Router logs timestamp

32

Header with Record Route Option

Route recorded

Intermediate routers append IPs

33

Header with Source Route Option

Strict/loose source routing

Packet follows specified path

34

Header with Security Option

Security level set

Used in classified networks

35

Header with Router Alert Option

Routers inspect packet

Used for RSVP, IGMP

36

Header with End of Option List

Properly terminated options

Packet accepted

37

Header with No Operation Option

Padding between options

Packet accepted

38

Header with Invalid Option Code

Unknown option

Packet dropped or ignored

39

Header with Overlapping Options

Options overlap

Packet dropped

40

Header with Excessive Options

IHL > 15

Packet dropped

41

Header with Reserved Bits Set

Reserved bits ? 0

Packet dropped or logged

42

Header with All Fields Zero

Empty header

Packet dropped

43

Header with Max Total Length

65535 bytes

Packet accepted if supported

44

Header with Min Total Length

20 bytes

Header only, no data

45

Header with Fragmented Packet

MF set, offset > 0

Reassembly required

46

Header with Last Fragment

MF = 0, offset > 0

Final fragment

47

Header with First Fragment

MF = 1, offset = 0

First fragment

48

Header with Non-Fragmented Packet

MF = 0, offset = 0

Single packet

49

Header with DF Set and Large Packet

DF = 1, size > MTU

ICMP Fragmentation Needed sent

50

Header with DF Cleared and Large Packet

DF = 0, size > MTU

Packet fragmented

Packet Routing - Testcases

Packet Routing - Test Cases

#

Test Case

Description

Expected Result

1

Route to Directly Connected Network

Destination in local subnet

Packet delivered directly

2

Route to Remote Network

Destination outside local subnet

Packet forwarded to next hop

3

No Route to Host

Destination not in routing table

ICMP Destination Unreachable sent

4

Default Route Present

No specific route, default exists

Packet forwarded via default gateway

5

Default Route Missing

No specific or default route

Packet dropped

6

Static Route Configured

Manual route entry

Packet follows static route

7

Dynamic Route Learned

Route via OSPF/RIP

Packet follows dynamic route

8

Multiple Routes to Destination

Equal-cost paths

Load balancing or ECMP used

9

Route with Lower Metric

Multiple routes, different metrics

Packet follows lowest metric route

10

Route with Administrative Distance

Conflicting routes

Route with lowest AD used

11

TTL = 1

TTL expires at router

ICMP Time Exceeded sent

12

TTL > 1

TTL decremented, packet forwarded

Packet continues routing

13

TTL = 0

Packet arrives with TTL 0

Packet dropped

14

Packet Fragmented

Size > MTU, DF not set

Packet fragmented and forwarded

15

Packet with DF Set and Size > MTU

DF = 1, size too large

ICMP Fragmentation Needed sent

16

Packet with Valid Checksum

Header checksum correct

Packet forwarded

17

Packet with Invalid Checksum

Header checksum incorrect

Packet dropped

18

Packet with Loopback Address

Destination = 127.0.0.1

Packet not routed

19

Packet with Broadcast Address

Destination = 255.255.255.255

Packet broadcasted locally

20

Packet with Multicast Address

Destination = 224.0.0.1

Routed to multicast group members

21

Packet with Private Address

Destination = 192.168.x.x

Routed within private network

22

Packet with Public Address

Destination = 8.8.8.8

Routed to internet

23

Packet with NAT Translation

Source/destination translated

Packet routed post-translation

24

Packet with PAT Translation

Port-based NAT applied

Routed with port mapping

25

Packet with Policy-Based Routing

Route based on policy

Packet follows policy route

26

Packet with ACL Deny

ACL blocks destination

Packet dropped

27

Packet with ACL Permit

ACL allows destination

Packet forwarded

28

Packet with QoS Tag

DSCP/ToS set

Packet prioritized in routing

29

Packet with Routing Loop

TTL expires in loop

ICMP Time Exceeded sent

30

Packet with ICMP Redirect

Better route exists

Host updates route

31

Packet with Source Routing Option

Strict/loose source route

Packet follows specified path

32

Packet with Invalid Source IP

Source = 0.0.0.0

Packet dropped

33

Packet with Invalid Destination IP

Destination = 0.0.0.0

Packet dropped

34

Packet with Unreachable Next Hop

Next hop not reachable

ICMP Destination Unreachable sent

35

Packet with ARP Resolution

MAC resolved for next hop

Packet forwarded

36

Packet with ARP Failure

No MAC for next hop

Packet queued or dropped

37

Packet with VRRP Gateway

Virtual gateway used

Packet routed via active router

38

Packet with HSRP Gateway

Hot standby router used

Packet routed via active router

39

Packet with BGP Route

Route learned via BGP

Packet routed to external network

40

Packet with OSPF Route

Route learned via OSPF

Packet routed internally

41

Packet with RIP Route

Route learned via RIP

Packet routed with hop count

42

Packet with Static and Dynamic Route

Both exist

Static route preferred

43

Packet with Route Flap

Route changes frequently

Packet may be dropped or delayed

44

Packet with Converged Route

Routing table stable

Packet routed normally

45

Packet with Blackhole Route

Route to null interface

Packet dropped silently

46

Packet with Loop Prevention

TTL or split horizon used

Loop avoided

47

Packet with Route Redistribution

Between protocols

Packet routed across domains

48

Packet with Route Summarization

Aggregated route used

Packet routed efficiently

49

Packet with Route Filtering

Route denied by filter

Packet dropped

50

Packet with Route Preference Change

Admin distance updated

Packet follows new preferred route

Fragmentation - Testcases

Fragmentation - Test Cases

#

Test Case

Description

Expected Result

1

Packet Size > MTU, DF = 0

Fragmentation allowed

Packet is fragmented

2

Packet Size > MTU, DF = 1

Fragmentation not allowed

ICMP Fragmentation Needed sent

3

Packet Size ? MTU

No fragmentation needed

Packet forwarded as-is

4

First Fragment Sent

Offset = 0, MF = 1

Router forwards first fragment

5

Middle Fragment Sent

Offset > 0, MF = 1

Router forwards middle fragment

6

Last Fragment Sent

MF = 0

Router forwards last fragment

7

All Fragments Received

All fragments arrive

Host reassembles packet

8

Missing Fragment

One fragment lost

Reassembly fails, packet dropped

9

Fragment Timeout

Fragments delayed

Reassembly times out, packet dropped

10

Overlapping Fragments

Fragments overlap

Host handles or drops based on policy

11

Fragment Offset Not Multiple of 8

Misaligned offset

Packet dropped

12

Fragment Offset = 0

First fragment

Reassembly starts

13

Fragment Offset > 0

Not first fragment

Waits for earlier fragments

14

MF Bit Set

More fragments follow

Host waits for next fragment

15

MF Bit Cleared

Last fragment

Host completes reassembly

16

Fragmented Packet with Valid Checksum

Checksum correct

Packet accepted

17

Fragmented Packet with Invalid Checksum

Checksum incorrect

Packet dropped

18

Fragmented Packet with TTL = 1

TTL expires

ICMP Time Exceeded sent

19

Fragmented Packet with TTL > 1

TTL decremented

Packet forwarded

20

Fragmented Packet with Options

Options in first fragment

Options processed

21

Fragmented Packet with Options in Middle Fragment

Options missing

Packet dropped

22

Fragmented Packet with Padding

Padding present

Packet accepted

23

Fragmented Packet with No Padding

Misaligned data

Packet dropped

24

Fragmented Packet with Duplicate Fragments

Same fragment resent

Host handles gracefully

25

Fragmented Packet with Out-of-Order Fragments

Fragments arrive out of order

Host reassembles correctly

26

Fragmented Packet with Reassembly Buffer Overflow

Too many fragments

Packet dropped

27

Fragmented Packet with Reassembly Buffer Exhaustion

Multiple packets reassembling

Some packets dropped

28

Fragmented Packet with Source Routing

Source route option

Routing follows specified path

29

Fragmented Packet with Record Route

Route recorded

Option processed in first fragment

30

Fragmented Packet with Timestamp Option

Timestamp recorded

Option processed in first fragment

31

Fragmented Packet with Invalid Header Length

IHL incorrect

Packet dropped

32

Fragmented Packet with Invalid Total Length

Length mismatch

Packet dropped

33

Fragmented Packet with Reserved Flags Set

Reserved bit = 1

Packet dropped

34

Fragmented Packet with Unknown Protocol

Protocol not supported

Packet dropped

35

Fragmented Packet with Loopback Address

Destination = 127.0.0.1

Packet not routed

36

Fragmented Packet with Broadcast Address

Destination = 255.255.255.255

Packet broadcasted

37

Fragmented Packet with Multicast Address

Destination = 224.0.0.1

Packet forwarded to group

38

Fragmented Packet with Private Address

Destination = 192.168.x.x

Routed within private network

39

Fragmented Packet with Public Address

Destination = 8.8.8.8

Routed to internet

40

Fragmented Packet with NAT

Translated IP

Fragments handled by NAT device

41

Fragmented Packet with PAT

Port-based NAT

Reassembly before translation

42

Fragmented Packet with Firewall

Firewall inspects fragments

Policy applied per fragment

43

Fragmented Packet with IDS/IPS

Security device inspects fragments

Reassembly for inspection

44

Fragmented Packet with VPN

Encrypted tunnel

Fragmentation handled before encryption

45

Fragmented Packet with MPLS

MPLS label added

Fragmentation handled before encapsulation

46

Fragmented Packet with QoS

DSCP marked

QoS applied per fragment

47

Fragmented Packet with Logging Enabled

Logging active

Fragmentation events logged

48

Fragmented Packet with ICMP Error

Error in fragment

ICMP sent to source

49

Fragmented Packet with Reassembly Success

All fragments arrive

Original packet reconstructed

50

Fragmented Packet with Reassembly Failure

One or more fragments lost

Packet dropped, ICMP may be sent

Connectionless Protocol - Testcases

Connectionless Protocol - Test Cases

#

Test Case

Description

Expected Result

1

Send Packet Without Handshake

No session setup

Packet transmitted immediately

2

Send Packet to Unreachable Host

No connection check

Packet sent, ICMP error may return

3

Send Packet Without Acknowledgment

No ACK expected

Sender does not wait for response

4

Send Packet to Closed Port

No session awareness

ICMP Port Unreachable may be returned

5

Send Packet with No State Tracking

Stateless delivery

Router does not track session

6

Send Packet with No Retransmission

Packet lost

No automatic retry

7

Send Packet with No Flow Control

High traffic

No congestion management by IPv4

8

Send Packet with No Ordering

Multiple packets sent

May arrive out of order

9

Send Packet with No Delivery Guarantee

Packet dropped

No recovery mechanism

10

Send Packet to Broadcast Address

One-to-many delivery

No connection to each host

11

Send Packet to Multicast Address

One-to-group delivery

No session with group members

12

Send Packet with No Session Teardown

No FIN or RST

No connection closure needed

13

Send Packet with No Keepalive

No periodic messages

No connection maintenance

14

Send Packet with No Handshake Delay

Immediate transmission

Low latency

15

Send Packet with No Congestion Avoidance

Network congested

IPv4 does not throttle

16

Send Packet with No Error Recovery

Packet corrupted

No retransmission

17

Send Packet with No Sequence Number

No tracking of order

Receiver must handle ordering

18

Send Packet with No Acknowledgment Number

No ACK field

Stateless communication

19

Send Packet with No Session ID

No unique session identifier

Stateless routing

20

Send Packet with No Connection Timeout

No timeout tracking

Stateless behavior

21

Send Packet with No Session Establishment

No SYN or handshake

Stateless delivery

22

Send Packet with No Session Termination

No FIN or teardown

Stateless delivery

23

Send Packet with No Session Recovery

Session interrupted

No recovery mechanism

24

Send Packet with No Session Persistence

No session memory

Stateless per packet

25

Send Packet with No Session Authentication

No identity check

No built-in security

26

Send Packet with No Session Encryption

No encryption

Plaintext delivery

27

Send Packet with No NAT Awareness

NAT modifies IP

IPv4 unaware of session state

28

Send Packet with No Firewall Session Tracking

Stateless firewall

Filters per packet

29

Send Packet with No Load Balancer Affinity

Stateless load balancing

Packets may go to different servers

30

Send Packet with No Application Layer Awareness

IPv4 unaware of app state

Stateless delivery

31

Send Packet with No Transport Layer Coordination

IPv4 independent of TCP/UDP

Stateless delivery

32

Send Packet with No Session Logs

No session tracking

Logs only per packet

33

Send Packet with No Session Metrics

No session stats

Only packet-level metrics

34

Send Packet with No Session Timeout Handling

No timeout logic

Stateless delivery

35

Send Packet with No Session Reuse

Each packet independent

No reuse of state

36

Send Packet with No Session Negotiation

No negotiation of parameters

Stateless delivery

37

Send Packet with No Session Buffering

No buffering

Immediate forwarding

38

Send Packet with No Session Synchronization

No sync between sender/receiver

Stateless delivery

39

Send Packet with No Session Monitoring

No session health check

Stateless delivery

40

Send Packet with No Session Redundancy

No failover

Packet lost if path fails

41

Send Packet with No Session Multiplexing

No session ID

No multiplexing at IPv4 level

42

Send Packet with No Session Fragmentation Awareness

Fragmented packets

Reassembly at receiver only

43

Send Packet with No Session Compression

No compression

Full-size packets

44

Send Packet with No Session Prioritization

No QoS at session level

All packets treated equally

45

Send Packet with No Session Replay Protection

No anti-replay

Stateless delivery

46

Send Packet with No Session Integrity Check

No end-to-end integrity

Only header checksum

47

Send Packet with No Session Authentication

No identity verification

Stateless delivery

48

Send Packet with No Session Authorization

No access control

Stateless delivery

49

Send Packet with No Session Accounting

No usage tracking

Stateless delivery

50

Send Packet with No Session Lifecycle

No session start/end

Stateless per packet

Subnetting - Testcases

Subnetting - Test Cases

#

Test Case

Description

Expected Result

1

Create Subnet with /24

Subnet mask 255.255.255.0

256 IPs, 254 usable

2

Create Subnet with /30

Subnet mask 255.255.255.252

4 IPs, 2 usable

3

Create Subnet with /32

Single host subnet

Only one usable IP

4

Create Subnet with /16

Subnet mask 255.255.0.0

65,536 IPs, 65,534 usable

5

Create Subnet with /8

Subnet mask 255.0.0.0

16,777,216 IPs

6

Invalid Subnet Mask /33

Beyond IPv4 range

Subnet rejected

7

Overlapping Subnets

Two subnets share IPs

Routing conflict detected

8

Non-overlapping Subnets

Distinct IP ranges

No conflict

9

Subnet with Reserved IPs

Includes 0.0.0.0 or 255.255.255.255

Reserved IPs excluded

10

Subnet with Private IP Range

192.168.0.0/16

Valid private subnet

11

Subnet with Public IP Range

8.8.8.0/24

Routable on internet

12

Subnet with Broadcast Address

Last IP in subnet

Used for broadcast only

13

Subnet with Network Address

First IP in subnet

Reserved for network ID

14

Subnet with Valid Gateway

Assign gateway IP

Host can reach external networks

15

Subnet with Invalid Gateway

Gateway outside subnet

Routing fails

16

Subnet with DHCP Scope

DHCP assigns IPs within subnet

Dynamic allocation works

17

Subnet with Static IPs

Manual IP assignment

IPs remain fixed

18

Subnet with VLAN Tagging

Subnet scoped to VLAN

Traffic isolated per VLAN

19

Subnet with NAT

Internal subnet mapped to public IP

Address translation occurs

20

Subnet with ACL

Access control applied

Traffic filtered by subnet

21

Subnet with Firewall Rules

Rules applied to subnet

Traffic permitted or denied

22

Subnet with Routing Table Entry

Subnet added to route table

Traffic routed correctly

23

Subnet with Static Route

Manual route to subnet

Traffic follows defined path

24

Subnet with Dynamic Route

Learned via protocol

Traffic routed dynamically

25

Subnet with CIDR Notation

Subnet defined as /27

32 IPs, 30 usable

26

Subnet with Subnet Zero

First subnet used

Allowed in modern networks

27

Subnet with All-Ones Subnet

Last subnet used

Allowed in modern networks

28

Subnet with Class A Address

10.0.0.0/8

Valid private subnet

29

Subnet with Class B Address

172.16.0.0/12

Valid private subnet

30

Subnet with Class C Address

192.168.1.0/24

Valid private subnet

31

Subnet with Class D Address

224.0.0.0/4

Reserved for multicast

32

Subnet with Class E Address

240.0.0.0/4

Reserved for experimental use

33

Subnet with Loopback Address

127.0.0.0/8

Used for local testing

34

Subnet with Link-Local Address

169.254.0.0/16

Used for auto-configuration

35

Subnet with Fragmented Packets

MTU exceeded

Packet fragmented within subnet

36

Subnet with ARP Resolution

MAC resolved for IP

Host reachable on LAN

37

Subnet with ARP Conflict

Duplicate IP detected

Warning triggered

38

Subnet with ICMP Echo

Ping IP in subnet

Host responds if reachable

39

Subnet with ICMP Unreachable

Ping unreachable IP

ICMP error returned

40

Subnet with SNMP Monitoring

Subnet monitored

Usage and status tracked

41

Subnet with Logging Enabled

Events logged

IP assignments recorded

42

Subnet with VPN

Subnet scoped to VPN

Traffic isolated and encrypted

43

Subnet with MPLS

Subnet tunneled via MPLS

Efficient routing

44

Subnet with QoS Policy

Traffic prioritized

Bandwidth managed per subnet

45

Subnet with Load Balancer

IPs distributed across servers

Traffic balanced

46

Subnet with Failover

Redundant gateway

Traffic rerouted on failure

47

Subnet with IPv6 Transition

Dual-stack configuration

IPv4 subnet coexists with IPv6

48

Subnet with DNS Integration

DNS resolves IPs in subnet

Hostnames mapped correctly

49

Subnet with Routing Loop

Misconfigured routes

TTL expires, ICMP sent

50

Subnet with Route Summarization

Multiple subnets aggregated

Efficient routing table entry

NAT Compatibility - Testcases

NAT Compatibility - Test Cases

#

Test Case

Description

Expected Result

1

Basic NAT Translation

Private IP translated to public IP

Packet forwarded with new source IP

2

Static NAT Mapping

One-to-one IP mapping

Always uses same public IP

3

Dynamic NAT Mapping

IP from pool assigned

IP assigned dynamically

4

PAT (NAT Overload)

Multiple private IPs share one public IP

Port numbers used for differentiation

5

NAT with TCP Traffic

TCP session initiated

NAT tracks and translates session

6

NAT with UDP Traffic

UDP datagram sent

NAT translates and maintains mapping

7

NAT with ICMP Echo Request

Ping sent

NAT translates ICMP identifiers

8

NAT with ICMP Error Message

ICMP error returned

NAT translates embedded IP header

9

NAT with FTP Active Mode

Control and data channels used

NAT handles embedded IP in payload

10

NAT with FTP Passive Mode

Client initiates data connection

NAT handles port mapping

11

NAT with SIP Protocol

VoIP session initiated

NAT handles dynamic port allocation

12

NAT with H.323 Protocol

Video call initiated

NAT handles multiple ports and IPs

13

NAT with DNS Query

DNS request sent

NAT translates source IP

14

NAT with DNS Response

DNS reply received

NAT maps response to correct client

15

NAT with VPN Tunnel

IPsec tunnel initiated

NAT-T (NAT Traversal) required

16

NAT with GRE Tunnel

GRE encapsulated traffic

NAT must support GRE

17

NAT with PPTP Tunnel

VPN using PPTP

NAT handles control and data channels

18

NAT with IP Fragmentation

Fragmented packet sent

NAT reassembles before translation

19

NAT with Large Packet

Packet > MTU

NAT fragments or drops if DF set

20

NAT with TTL Expiry

TTL = 1

NAT decrements TTL and sends ICMP

21

NAT with Port Exhaustion

All ports used

New connections dropped

22

NAT with Port Reuse

Same port reused for different IPs

NAT tracks sessions separately

23

NAT with Session Timeout

Inactive session

Mapping removed after timeout

24

NAT with Persistent Mapping

Session kept alive

Mapping retained

25

NAT with Asymmetric Routing

Return path bypasses NAT

Response dropped

26

NAT with Load Balancer

NAT behind load balancer

Mapping maintained per flow

27

NAT with Firewall

NAT and firewall coexist

Rules applied post-translation

28

NAT with ACL

Access control on translated IPs

ACLs applied to public IPs

29

NAT with Logging Enabled

NAT events logged

Translation entries recorded

30

NAT with SNMP Monitoring

NAT table monitored

Entries visible via SNMP

31

NAT with Static Port Mapping

Specific port mapped

Always uses same external port

32

NAT with Dynamic Port Mapping

Port assigned dynamically

Port changes per session

33

NAT with Overlapping Subnets

Same private IPs in different sites

NAT differentiates by interface

34

NAT with Dual Stack (IPv4/IPv6)

IPv4 NAT only

IPv6 bypasses NAT

35

NAT with Hairpinning

Internal host accesses another via public IP

NAT redirects internally

36

NAT with Loopback Traffic

Host accesses itself via public IP

NAT handles loopback correctly

37

NAT with DNS ALG

DNS ALG enabled

Embedded IPs rewritten

38

NAT with SIP ALG

SIP ALG enabled

SIP headers rewritten

39

NAT with Application Proxy

Proxy handles session

NAT sees only proxy IP

40

NAT with Port Forwarding

External port mapped to internal host

Traffic redirected correctly

41

NAT with DMZ Host

All ports forwarded to one host

Host receives all unsolicited traffic

42

NAT with Multiple Interfaces

NAT on multiple WAN links

Mapping per interface

43

NAT with Failover

Primary link fails

NAT continues on backup link

44

NAT with Redundancy

Stateful failover

NAT table synced between devices

45

NAT with High Availability

Active/standby NAT

Seamless transition

46

NAT with QoS

Traffic prioritized

NAT preserves QoS markings

47

NAT with IPv4 Broadcast

Broadcast sent

NAT does not forward broadcast

48

NAT with Multicast

Multicast sent

NAT may not support multicast

49

NAT with ICMP Redirect

Redirect received

NAT ignores or drops

50

NAT with Fragmented ICMP

ICMP fragmented

NAT reassembles before translation

Broadcast Support - Testcases

Broadcast Support - Test Cases

#

Test Case

Description

Expected Result

1

Send Limited Broadcast

Destination = 255.255.255.255

Packet delivered to all hosts on local network

2

Send Directed Broadcast

Destination = subnet broadcast (e.g., 192.168.1.255)

Packet delivered to all hosts in subnet

3

Send Broadcast with Valid Source

Source IP is valid

Packet accepted by receivers

4

Send Broadcast with Invalid Source

Source IP = 0.0.0.0

Packet dropped

5

Broadcast Packet with TTL = 1

TTL expires after one hop

Packet not forwarded

6

Broadcast Packet with TTL > 1

TTL > 1

Packet still not forwarded (broadcasts not routed)

7

Broadcast Packet with UDP

UDP datagram broadcasted

All hosts receive

8

Broadcast Packet with TCP

TCP not typically used

Packet dropped or ignored

9

Broadcast Packet with ICMP

ICMP Echo Request to broadcast

May be dropped by hosts

10

Broadcast Packet with ARP

ARP request broadcasted

All hosts on LAN receive

11

Broadcast Packet with DHCP Discover

DHCP Discover sent

All DHCP servers receive

12

Broadcast Packet with BOOTP

BOOTP request broadcasted

Server responds if available

13

Broadcast Packet with NetBIOS

NetBIOS name query broadcasted

All Windows hosts respond

14

Broadcast Packet with SNMP Trap

Trap sent to broadcast address

All SNMP listeners receive

15

Broadcast Packet with Custom App

App sends UDP broadcast

All listening clients receive

16

Broadcast Packet with VLAN

Broadcast scoped to VLAN

Only VLAN members receive

17

Broadcast Packet with Trunk Port

Tagged broadcast

Forwarded to correct VLANs

18

Broadcast Packet with Access Port

Untagged broadcast

Forwarded within VLAN

19

Broadcast Packet with ACL Permit

ACL allows broadcast

Packet forwarded

20

Broadcast Packet with ACL Deny

ACL blocks broadcast

Packet dropped

21

Broadcast Packet with Firewall

Firewall allows broadcast

Packet forwarded

22

Broadcast Packet Blocked by Firewall

Firewall blocks broadcast

Packet dropped

23

Broadcast Packet with NAT

NAT device receives broadcast

Packet not translated or forwarded

24

Broadcast Packet with Router

Router receives broadcast

Packet not forwarded to other networks

25

Broadcast Packet with Switch

Switch floods broadcast

All ports receive except source

26

Broadcast Packet with Hub

Hub repeats broadcast

All ports receive

27

Broadcast Packet with Wireless AP

Broadcast sent over Wi-Fi

All wireless clients receive

28

Broadcast Packet with VPN

Broadcast sent over VPN

May not be forwarded

29

Broadcast Packet with MPLS

MPLS network

Broadcast not supported

30

Broadcast Packet with IPv6

IPv6 used

Broadcast not supported (uses multicast)

31

Broadcast Packet with Logging Enabled

Logging active

Broadcast events logged

32

Broadcast Packet with Monitoring Tool

Tool captures broadcast

Packet visible in capture

33

Broadcast Packet with Packet Sniffer

Wireshark running

Broadcast packet captured

34

Broadcast Packet with Loopback Interface

Sent to 127.0.0.1

Packet not broadcasted

35

Broadcast Packet with Broadcast Storm

Excessive broadcasts

Network congestion occurs

36

Broadcast Packet with Rate Limiting

Broadcasts throttled

Excess packets dropped

37

Broadcast Packet with Storm Control

Switch limits broadcast rate

Excess packets dropped

38

Broadcast Packet with QoS

QoS policy applied

Broadcasts prioritized or limited

39

Broadcast Packet with Fragmentation

Large broadcast fragmented

Reassembled at receiver

40

Broadcast Packet with Invalid Checksum

Corrupted header

Packet dropped

41

Broadcast Packet with IP Options

Options present

Packet processed if supported

42

Broadcast Packet with Source Routing

Source route option

Packet dropped or ignored

43

Broadcast Packet with TTL = 0

TTL expired

Packet dropped immediately

44

Broadcast Packet with ICMP Redirect

Sent to broadcast

Packet dropped

45

Broadcast Packet with DHCP Relay

Relay agent forwards

Packet unicast to DHCP server

46

Broadcast Packet with Proxy ARP

Proxy responds

Host receives reply

47

Broadcast Packet with Duplicate IP Detection

ARP probe broadcasted

Conflict detected if IP in use

48

Broadcast Packet with Gratuitous ARP

ARP broadcasted without request

Used for IP conflict detection

49

Broadcast Packet with Wake-on-LAN

Magic packet broadcasted

Target device wakes up

50

Broadcast Packet with Legacy Protocol

NetBEUI or similar

Broadcast used for discovery

Protocol Identification - Testcases

Protocol Identification - Test Cases

#

Test Case

Description

Expected Result

1

Protocol = 1 (ICMP)

IPv4 packet with ICMP

Routed to ICMP handler

2

Protocol = 6 (TCP)

IPv4 packet with TCP

Routed to TCP stack

3

Protocol = 17 (UDP)

IPv4 packet with UDP

Routed to UDP stack

4

Protocol = 2 (IGMP)

IPv4 packet with IGMP

Routed to IGMP handler

5

Protocol = 89 (OSPF)

IPv4 packet with OSPF

Routed to OSPF process

6

Protocol = 47 (GRE)

IPv4 packet with GRE

Routed to GRE tunnel handler

7

Protocol = 50 (ESP)

IPv4 packet with IPsec ESP

Routed to IPsec stack

8

Protocol = 51 (AH)

IPv4 packet with IPsec AH

Routed to IPsec stack

9

Protocol = 132 (SCTP)

IPv4 packet with SCTP

Routed to SCTP stack

10

Protocol = 115 (L2TP)

IPv4 packet with L2TP

Routed to L2TP handler

11

Protocol = 0

Reserved value

Packet dropped or logged

12

Protocol = 255

Reserved for testing

Packet dropped or logged

13

Protocol = Unknown Value

Unsupported protocol

Packet dropped

14

Protocol = 6 with Invalid TCP Header

Malformed TCP

Packet dropped

15

Protocol = 17 with Invalid UDP Header

Malformed UDP

Packet dropped

16

Protocol = 1 with Echo Request

ICMP Echo Request

ICMP reply generated

17

Protocol = 1 with Destination Unreachable

ICMP error

Routed to ICMP handler

18

Protocol = 6 with SYN Packet

TCP handshake

Routed to TCP stack

19

Protocol = 6 with FIN Packet

TCP termination

Routed to TCP stack

20

Protocol = 17 with DNS Query

UDP DNS request

Routed to DNS service

21

Protocol = 17 with DHCP Discover

UDP broadcast

Routed to DHCP server

22

Protocol = 6 with HTTP Traffic

TCP port 80

Routed to web server

23

Protocol = 6 with HTTPS Traffic

TCP port 443

Routed to TLS handler

24

Protocol = 6 with FTP Traffic

TCP port 21

Routed to FTP server

25

Protocol = 6 with SSH Traffic

TCP port 22

Routed to SSH daemon

26

Protocol = 6 with SMTP Traffic

TCP port 25

Routed to mail server

27

Protocol = 6 with POP3 Traffic

TCP port 110

Routed to mail client

28

Protocol = 6 with IMAP Traffic

TCP port 143

Routed to mail client

29

Protocol = 6 with Telnet Traffic

TCP port 23

Routed to Telnet server

30

Protocol = 6 with RDP Traffic

TCP port 3389

Routed to RDP service

31

Protocol = 6 with SQL Traffic

TCP port 1433

Routed to database server

32

Protocol = 6 with Malformed TCP Flags

Invalid flags

Packet dropped or logged

33

Protocol = 6 with TCP Reset

TCP RST flag

Connection reset

34

Protocol = 6 with TCP Retransmission

Duplicate segment

Handled by TCP stack

35

Protocol = 17 with TFTP Traffic

UDP port 69

Routed to TFTP server

36

Protocol = 17 with SNMP Traffic

UDP port 161

Routed to SNMP agent

37

Protocol = 17 with NTP Traffic

UDP port 123

Routed to NTP service

38

Protocol = 17 with Syslog Traffic

UDP port 514

Routed to logging service

39

Protocol = 6 with Fragmented Packet

TCP in fragments

Reassembled before processing

40

Protocol = 17 with Fragmented Packet

UDP in fragments

Reassembled before processing

41

Protocol = 6 with NAT

TCP translated

Protocol field preserved

42

Protocol = 17 with NAT

UDP translated

Protocol field preserved

43

Protocol = 1 with Firewall

ICMP filtered

Packet dropped or allowed

44

Protocol = 6 with Firewall

TCP filtered

Packet dropped or allowed

45

Protocol = 17 with Firewall

UDP filtered

Packet dropped or allowed

46

Protocol = 6 with QoS

TCP prioritized

QoS applied

47

Protocol = 17 with QoS

UDP prioritized

QoS applied

48

Protocol = 6 with Logging Enabled

TCP packet logged

Protocol field recorded

49

Protocol = 17 with Logging Enabled

UDP packet logged

Protocol field recorded

50

Protocol = 6 with IDS/IPS

TCP packet inspected

Protocol used for rule matching

TTL (Time to Live) - Testcases

TTL (Time to Live) - Test Cases

#

Test Case

Description

Expected Result

1

TTL = 64

Standard TTL value

Packet forwarded, TTL decremented

2

TTL = 1

Minimum valid TTL

Packet dropped at first hop, ICMP Time Exceeded sent

3

TTL = 0

Invalid TTL

Packet dropped immediately

4

TTL = 255

Maximum TTL

Packet forwarded, TTL decremented

5

TTL Decrement by Router

Router receives packet

TTL reduced by 1

6

TTL Expiry at Router

TTL reaches 0

ICMP Time Exceeded sent to source

7

TTL with Looping Route

Packet loops

TTL eventually expires

8

TTL with Static Route

TTL decremented normally

Packet forwarded

9

TTL with Dynamic Route

TTL decremented normally

Packet forwarded

10

TTL with Fragmented Packet

Each fragment has same TTL

TTL decremented per fragment

11

TTL with NAT

TTL decremented before translation

NAT does not reset TTL

12

TTL with Firewall

TTL checked for filtering

Packet allowed or dropped

13

TTL with ACL

ACL does not inspect TTL

Packet filtered based on IP/port

14

TTL with VPN Tunnel

TTL decremented before encapsulation

Tunnel endpoint receives packet

15

TTL with GRE Tunnel

TTL decremented before encapsulation

GRE header added

16

TTL with IPsec Tunnel

TTL decremented before encryption

Packet encrypted and forwarded

17

TTL with MPLS

TTL copied to MPLS label

Decremented per hop

18

TTL with ICMP Echo Request

Ping with TTL = 1

ICMP Time Exceeded received

19

TTL with ICMP Echo Reply

Ping reply TTL = 64

Reply received with TTL intact

20

TTL with Traceroute

TTL incremented per probe

ICMP Time Exceeded received from each hop

21

TTL with Broadcast Packet

TTL = 1

Packet not forwarded beyond subnet

22

TTL with Multicast Packet

TTL controls scope

Packet dropped after TTL expires

23

TTL with Loopback Address

TTL not decremented

Packet processed locally

24

TTL with Private Address

TTL decremented normally

Packet routed within private network

25

TTL with Public Address

TTL decremented normally

Packet routed to internet

26

TTL with Logging Enabled

TTL logged

TTL value recorded in logs

27

TTL with Monitoring Tool

TTL captured

TTL visible in packet capture

28

TTL with QoS

TTL not affected by QoS

Packet prioritized

29

TTL with Load Balancer

TTL decremented before forwarding

Load balancer does not reset TTL

30

TTL with Proxy

TTL decremented before proxy

Proxy may reset TTL

31

TTL with NAT Hairpinning

TTL decremented

Packet routed internally

32

TTL with TTL Expiry Logging

TTL = 1

Expiry logged by router

33

TTL with TTL-Based Filtering

TTL < threshold

Packet dropped

34

TTL with TTL-Based Routing

TTL used in policy

Packet routed based on TTL

35

TTL with TTL Reset by Device

Device resets TTL

Packet appears fresh

36

TTL with TTL Preservation

TTL unchanged by device

Packet continues with original TTL

37

TTL with TTL Manipulation Attack

TTL set low

Packet dropped early

38

TTL with TTL Spoofing Detection

TTL anomaly detected

Packet flagged or dropped

39

TTL with TTL Expiry Notification

ICMP Time Exceeded sent

Source notified of drop

40

TTL with TTL Expiry Suppression

ICMP disabled

Packet dropped silently

41

TTL with TTL in Fragmented Packet

All fragments have same TTL

TTL decremented per fragment

42

TTL with TTL in Reassembled Packet

TTL from first fragment used

Packet reassembled correctly

43

TTL with TTL in IPv6

Not applicable

IPv6 uses Hop Limit

44

TTL with TTL in IPv4 Header

TTL field = 8 bits

Value between 0255

45

TTL with TTL in Routing Loop Detection

TTL used to detect loops

Loop broken by TTL expiry

46

TTL with TTL in Path MTU Discovery

TTL not used

PMTUD uses DF bit and ICMP

47

TTL with TTL in BGP

TTL used in TTL Security Check

Protects against spoofing

48

TTL with TTL in OSPF

TTL = 1 for hello packets

Ensures packets stay on local link

49

TTL with TTL in RIP

TTL not used

RIP uses hop count

50

TTL with TTL in Application Layer

App reads TTL

Used for diagnostics or routing decisions

Classful Addressing (Legacy) - Testcases

Classful Addressing (Legacy) - Test Cases

#

Test Case

Description

Expected Result

1

Class A Address Assignment

Assign 10.0.0.1

Recognized as Class A

2

Class B Address Assignment

Assign 172.16.0.1

Recognized as Class B

3

Class C Address Assignment

Assign 192.168.1.1

Recognized as Class C

4

Class D Address Assignment

Assign 224.0.0.1

Recognized as multicast

5

Class E Address Assignment

Assign 240.0.0.1

Reserved, not routable

6

Class A Default Subnet Mask

255.0.0.0

Applied automatically

7

Class B Default Subnet Mask

255.255.0.0

Applied automatically

8

Class C Default Subnet Mask

255.255.255.0

Applied automatically

9

Class A Network Range

1.0.0.0 to 126.255.255.255

Valid Class A range

10

Class B Network Range

128.0.0.0 to 191.255.255.255

Valid Class B range

11

Class C Network Range

192.0.0.0 to 223.255.255.255

Valid Class C range

12

Class D Network Range

224.0.0.0 to 239.255.255.255

Multicast only

13

Class E Network Range

240.0.0.0 to 255.255.255.254

Reserved

14

Loopback Address

127.0.0.1

Not part of any class

15

Broadcast Address

255.255.255.255

Not class-specific

16

Class A with Custom Subnet

10.0.0.1/16

Subnetting applied

17

Class B with Custom Subnet

172.16.0.1/20

Subnetting applied

18

Class C with Custom Subnet

192.168.1.1/28

Subnetting applied

19

Invalid Class A Address

0.0.0.1

Reserved, not valid

20

Invalid Class B Address

127.0.0.1

Loopback, not Class B

21

Invalid Class C Address

223.255.255.256

Invalid octet

22

Class A with Host Bits All 0

10.0.0.0

Network address

23

Class A with Host Bits All 1

10.255.255.255

Broadcast address

24

Class B with Host Bits All 0

172.16.0.0

Network address

25

Class B with Host Bits All 1

172.16.255.255

Broadcast address

26

Class C with Host Bits All 0

192.168.1.0

Network address

27

Class C with Host Bits All 1

192.168.1.255

Broadcast address

28

Class D with TTL = 1

224.0.0.1

Local multicast only

29

Class D with TTL > 1

224.0.1.1

Multicast routed

30

Class E with Routing Attempt

240.0.0.1

Packet dropped

31

Class A with ARP Request

10.0.0.1

ARP resolves MAC

32

Class B with DHCP

172.16.0.1

DHCP assigns IP

33

Class C with NAT

192.168.1.1

NAT translates IP

34

Class A with ACL

10.0.0.1

ACL filters traffic

35

Class B with Firewall

172.16.0.1

Firewall rules applied

36

Class C with VPN

192.168.1.1

Routed through VPN

37

Class A with Routing Table

10.0.0.0/8

Route added

38

Class B with Static Route

172.16.0.0/16

Route configured

39

Class C with Dynamic Routing

192.168.1.0/24

Route learned

40

Class D with IGMP

224.0.0.1

Group membership managed

41

Class A with DNS

10.0.0.1

Resolves to hostname

42

Class B with SNMP

172.16.0.1

Device monitored

43

Class C with Syslog

192.168.1.1

Logs sent

44

Class A with ICMP

10.0.0.1

Ping successful

45

Class B with Traceroute

172.16.0.1

TTL decremented

46

Class C with Packet Capture

192.168.1.1

Traffic visible

47

Class D with Multicast App

224.0.0.1

App receives stream

48

Class A with Subnet Overlap

10.0.0.0/8 and 10.1.0.0/16

Conflict detected

49

Class B with Subnetting Violation

172.16.0.0/15

Not aligned with class

50

Class C with CIDR

192.168.1.0/26

CIDR overrides classful mask

  • Reference links