Port Numbers
What are UDP Port Numbers?
UDP port numbers identify specific applications or services on a host. Each port allows communication with a particular process or service.
Why are UDP Port Numbers useful?
They allow the operating system to route incoming UDP packets to the correct application, enabling multiple services to run simultaneously without interference.
How do UDP Port Numbers work?
UDP uses source and destination port numbers (16-bit each) in its header to send packets to the correct application. Ports range from 0 to 65535.
Where are UDP Port Numbers used?
Common UDP-based services use well-known ports:
53 – DNS
67/68 – DHCP
123 – NTP
161/162 – SNMP
500 – IPsec
Which OSI layer do UDP Port Numbers belong to?
UDP port numbers are part of the Transport Layer (Layer 4), where data is directed to the correct application process.
Are UDP Port Numbers Windows specific?
No, port numbers are part of the standard networking stack and are used on all operating systems including Windows, Linux, and macOS.
Are UDP Port Numbers Linux specific?
No, UDP port numbers are universally used in all OS environments. Linux assigns and manages them just like other OSes.
Which transport protocol uses Port Numbers in this way?
Both UDP and TCP use port numbers, but UDP does so without the overhead of connections or reliability mechanisms.
Are UDP Port Numbers used in client-server models?
Yes. In a typical model, the server listens on a fixed port, and the client uses an ephemeral port to initiate the request.
In this section, you are going to learn
Terminology
Version Info
setup
Port Numbers - Testcases
S.No |
Test Case |
Description |
Expected Result |
|---|---|---|---|
1 |
Valid Port Range |
Use port number between 065535 |
Packet accepted |
2 |
Reserved Port Usage |
Use reserved port (e.g., 53 for DNS) |
Packet routed to correct service |
3 |
Invalid Port Number |
Use port > 65535 |
Packet rejected |
4 |
Negative Port Number |
Use negative port |
Packet rejected |
5 |
Port Number Zero |
Use port 0 |
Packet accepted (source only) |
6 |
Port Conflict |
Use same port for multiple apps |
Apps may share or conflict |
7 |
Dynamic Port Allocation |
Use ephemeral port |
Port assigned dynamically |
8 |
Static Port Assignment |
Assign fixed port |
Packet routed correctly |
9 |
Port Reuse |
Enable socket reuse |
Multiple apps receive packet |
10 |
Port Binding Failure |
Bind to used port |
Binding fails |
11 |
Port Binding Success |
Bind to free port |
Binding succeeds |
12 |
Port Filtering |
Block specific port via firewall |
Packet dropped |
13 |
Port Forwarding |
Forward port via NAT |
Packet redirected correctly |
14 |
Port Scanning Detection |
Scan ports |
Detection triggered |
15 |
Port Range Scan |
Scan range of ports |
All open ports identified |
16 |
Port with Broadcast |
Send to broadcast address |
Packet sent to all on port |
17 |
Port with Multicast |
Send to multicast group |
Packet received by group on port |
18 |
Port with Loopback |
Send to loopback |
Packet received locally |
19 |
Port with IPv6 |
Use port with IPv6 |
Packet routed correctly |
20 |
Port with IPv4 |
Use port with IPv4 |
Packet routed correctly |
21 |
Port with DNS |
Use port 53 |
DNS service responds |
22 |
Port with DHCP |
Use port 67/68 |
DHCP service responds |
23 |
Port with SNMP |
Use port 161 |
SNMP service responds |
24 |
Port with TFTP |
Use port 69 |
TFTP service responds |
25 |
Port with NTP |
Use port 123 |
NTP service responds |
26 |
Port with RTP |
Use port 5004 |
RTP stream received |
27 |
Port with SIP |
Use port 5060 |
SIP service responds |
28 |
Port with Custom App |
Use custom port |
App receives packet |
29 |
Port with Logging |
Log port usage |
Port logged correctly |
30 |
Port with Monitoring Tool |
Use sniffer |
Port visible in capture |
31 |
Port with Encryption |
Encrypt payload |
Port remains visible |
32 |
Port with Compression |
Compress payload |
Port unaffected |
33 |
Port with NAT Traversal |
Use STUN/TURN |
Port mapped correctly |
34 |
Port with VPN |
Send through VPN |
Port preserved |
35 |
Port with VLAN |
Send on VLAN |
Port used correctly |
36 |
Port with QoS |
Apply QoS |
Port used for classification |
37 |
Port with Load Balancer |
Send through LB |
Port used for routing |
38 |
Port with Proxy |
Send through proxy |
Port preserved or translated |
39 |
Port with TTL |
TTL in IP header |
Port unaffected |
40 |
Port with Fragmentation |
Fragment packet |
Port info in each fragment |
41 |
Port with Delay |
Delay packet |
Port info preserved |
42 |
Port with Packet Loss |
Simulate loss |
Port info lost with packet |
43 |
Port with Retransmission |
Retransmit packet |
Port info reused |
44 |
Port with Bit Flip |
Flip bit in port field |
Packet misrouted or dropped |
45 |
Port with Header Tampering |
Modify header |
Port info corrupted |
46 |
Port with Logging Disabled |
Disable logging |
Port info not recorded |
47 |
Port with High Traffic |
Send many packets |
Port handles load |
48 |
Port with Low Traffic |
Send few packets |
Port remains open |
49 |
Port with Timeout |
Idle port |
Port may close |
50 |
Port with Error Handling |
Send to closed port |
ICMP error returned |
Reference links