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Common Network Port Numbers Flashcards: Protocols, TCP/UDP & Uses

Study 88 cards on common network ports, TCP/UDP transports, service uses, port ranges, and practical protocol distinctions.

Par Open Study Contributor

À propos de ce paquet

Build a practical map of common network service ports with 88 independently authored cards. Twelve foundation and distinction cards cover port roles, IANA ranges, independent TCP and UDP namespaces, assignment limits, conventional versus configured ports, client source ports, DNS transport behavior, DHCP endpoints, FTP channels, and common implicit-TLS pairs.

The remaining 76 cards practice 38 mappings in both useful directions: service → conventional or registered port, transport, and concise use; and port/transport → service and concise use. Coverage includes FTP control and active-mode data, SSH/SFTP, Telnet, SMTP relay, DNS, DHCPv4 server and client endpoints, TFTP, HTTP, Kerberos, POP3, NTP, the three NetBIOS services, IMAP, SNMP queries and notifications, BGP, LDAP, HTTPS including HTTP/3, direct-hosted SMB, IKE, syslog, SMTP submission, LDAPS, IMAPS, POP3S, Microsoft SQL Server, L2TP, PPTP, RADIUS authentication, MySQL, RDP, IPsec NAT Traversal, SIP, and PostgreSQL.

This is a focused recall deck, not a copy of the full IANA registry. It excludes exhaustive assignments, port-scanning or attack instructions, firewall policy, every vendor-specific alternate, dynamic service-discovery inventories, and the claim that a port number proves which application produced observed traffic. Registered, default, conventional, and common-use wording stays explicit because services can be reconfigured or negotiated elsewhere.

The sequence establishes the port model first, then mixes web, email, infrastructure, remote-access, file-transfer, network-management, directory, VPN, voice, Windows, and database families. Opposite directions for the same mapping stay at least 38 intervening cards apart. Near-duplicate DNS, DHCP, FTP, SNMP, NetBIOS, and IPsec cues keep at least three unrelated cards between them, and the TLS-pair distinction stays at least three unrelated cards from its closest overlapping mapping. The review scheduler handles continued spacing after installation.

Open Study Contributor independently authored the prompts, answers, mapping choices, organization, metadata, and cover from common networking knowledge checked against the current IANA Service Name and Transport Protocol Port Number Registry, relevant RFCs, and official vendor documentation. Organization and product names identify protocols, services, or sources only; no affiliation or endorsement is claimed. No competitor card text, certification questions, answer keys, course text, or source prose was copied.

The CC0 label applies to the original prompts, answers, organization, metadata, and generated cover to the extent applicable rights exist. It does not claim ownership of protocol facts, standards, organization names, product names, or third-party source material.

Cartes de ce paquet

  1. Carte 1

    Question

    What does a transport-layer port number identify?

    Réponse

    An application endpoint within a host for one transport protocol. The IP addresses, transport protocol, and source and destination ports together identify a communication flow.

  2. Carte 2

    Question

    Are TCP port 53 and UDP port 53 the same port?

    Réponse

    No. TCP and UDP have independent 16-bit port namespaces, so 53/TCP and 53/UDP are separate transport endpoints.

  3. Carte 3

    Question

    What is the IANA System Port range?

    Réponse

    0–1023. These are also called Well-Known Ports and are assigned by IANA under the stricter System Port procedures.

  4. Carte 4

    Question

    What is the IANA User Port range?

    Réponse

    1024–49151. These are also called Registered Ports and may be assigned by IANA to services.

  5. Carte 5

    Question

    What is the IANA Dynamic or Private Port range?

    Réponse

    49152–65535. IANA does not assign ports in this range; systems commonly use it for temporary or private endpoints.

  6. Carte 6

    Question

    Does an IANA port assignment prove what observed traffic is—or that it is safe?

    Réponse

    No. A registration is a naming convention, not traffic identification, authorization, or a security verdict. Verify the actual protocol and context.

  7. Carte 7

    Question

    Must a service use its registered or conventional port?

    Réponse

    No. Administrators and applications can choose another port, negotiate one dynamically, or discover it through mechanisms such as DNS SRV records.

  8. Carte 8

    Question

    What port roles are typical in a client-server connection?

    Réponse

    The server usually listens on a known destination port, while the client uses a temporary source port. Either side can be configured differently.

  9. Carte 9

    Question

    SSH and SFTP — common server port and transport?

    Réponse

    TCP 22. SSH provides encrypted remote access, and SFTP normally runs as a subsystem inside the same SSH connection.

  10. Carte 10

    Question

    53/UDP or 53/TCP — which service?

    Réponse

    DNS. Routine queries often use UDP, while full DNS implementations also support TCP; zone transfers use TCP.

  11. Carte 11

    Question

    SMTP relay between mail servers — common port and transport?

    Réponse

    TCP 25. SMTP uses it for server-to-server mail transfer; user mail submission normally uses port 587 or implicit TLS on 465.

  12. Carte 12

    Question

    HTTP without TLS — conventional port and transport?

    Réponse

    TCP 80 for conventional HTTP/1.1 and HTTP/2 connections. The service can be configured on another port.

  13. Carte 13

    Question

    67/UDP — which DHCPv4 endpoint?

    Réponse

    The DHCPv4 server endpoint. Clients send server-directed DHCP messages to UDP port 67.

  14. Carte 14

    Question

    21/TCP — which service and channel?

    Réponse

    FTP control. It carries commands and replies; file data uses a separate connection.

  15. Carte 15

    Question

    SNMP requests and responses — common agent port and transport?

    Réponse

    UDP 161. Managers commonly send queries to an SNMP agent there; other SNMP transports exist.

  16. Carte 16

    Question

    1433/TCP — which database service?

    Réponse

    Microsoft SQL Server's default instance. TCP 1433 is the default Database Engine port, but named or custom instances may use another port.

  17. Carte 17

    Question

    23/TCP — which remote-access protocol?

    Réponse

    Telnet. It provides a plaintext remote terminal session and does not protect credentials or traffic with encryption.

  18. Carte 18

    Question

    NTP — usual port and transport?

    Réponse

    UDP 123. NTP normally uses UDP for time synchronization; IANA also has a TCP 123 registration, but that is not the usual NTP transport.

  19. Carte 19

    Question

    Why must a general-purpose DNS implementation support both UDP and TCP?

    Réponse

    UDP handles most routine queries efficiently, while TCP handles cases such as zone transfers and responses that do not fit the chosen UDP path. Both use port 53.

  20. Carte 20

    Question

    POP3 — conventional port and transport?

    Réponse

    TCP 110. POP3 retrieves mail; it can upgrade with STLS, while implicit TLS uses TCP 995.

  21. Carte 21

    Question

    443/TCP or 443/UDP — which web service?

    Réponse

    HTTPS. HTTP/1.1 and HTTP/2 normally use TLS over TCP 443; HTTP/3 uses QUIC over UDP 443.

  22. Carte 22

    Question

    DHCPv4 client endpoint — port and transport?

    Réponse

    UDP 68. Servers send client-directed DHCPv4 messages to port 68.

  23. Carte 23

    Question

    69/UDP — which file-transfer protocol?

    Réponse

    TFTP. A client sends the initial read or write request to UDP 69; the transfer then continues with a server-selected UDP transfer identifier.

  24. Carte 24

    Question

    162/UDP — which network-management traffic?

    Réponse

    SNMP notifications, traditionally called traps. Notification receivers commonly listen on UDP 162.

  25. Carte 25

    Question

    MySQL classic protocol — default port and transport?

    Réponse

    TCP 3306. It is the default for classic MySQL client-server connections and can be reconfigured.

  26. Carte 26

    Question

    How do FTP control, active-mode data, and passive-mode data ports differ?

    Réponse

    Control uses TCP 21. The server side of the default active-mode data connection uses TCP 20, while passive mode negotiates another server port.

  27. Carte 27

    Question

    3389/TCP or 3389/UDP — which remote-desktop service?

    Réponse

    Microsoft Remote Desktop Protocol (RDP). TCP and UDP 3389 are the standard defaults, and the listening port can be changed.

  28. Carte 28

    Question

    Syslog's conventional UDP transport — port?

    Réponse

    UDP 514. Classic syslog over UDP has no delivery guarantee; TCP 514 is registered to the shell service, not syslog.

  29. Carte 29

    Question

    How do DHCPv4 server and client ports pair up?

    Réponse

    UDP 67 is the server port, and UDP 68 is the client port. Client-to-server messages target 67; server-to-client messages target 68.

  30. Carte 30

    Question

    IMAP — conventional port and transport?

    Réponse

    TCP 143. IMAP accesses and manages mail on a server; implicit TLS uses TCP 993.

  31. Carte 31

    Question

    445/TCP — which file-sharing service?

    Réponse

    Direct-hosted SMB. Modern SMB servers commonly listen on TCP 445 without the older NetBIOS session layer.

  32. Carte 32

    Question

    88/UDP or 88/TCP — which authentication protocol?

    Réponse

    Kerberos. Clients and Key Distribution Centers support both transports; TCP also handles requests or replies too large for UDP.

  33. Carte 33

    Question

    FTP's default active-mode data connection — server-side port and transport?

    Réponse

    TCP 20. This is the server's default source port for active-mode data; passive FTP negotiates another server port.

  34. Carte 34

    Question

    BGP — standard operational port and transport?

    Réponse

    TCP 179. RFC 4271 defines BGP peer sessions over TCP; IANA separately retains a UDP 179 registry entry.

  35. Carte 35

    Question

    5432/TCP — which database service?

    Réponse

    PostgreSQL. TCP 5432 is the customary default server port, but an installation can choose another port.

  36. Carte 36

    Question

    IKE for IPsec — initial port and transport?

    Réponse

    UDP 500. IKE normally begins there; NAT traversal commonly moves subsequent IKE and encapsulated ESP traffic to UDP 4500.

  37. Carte 37

    Question

    NetBIOS Name Service — common port and transport?

    Réponse

    UDP 137. It supports NetBIOS name registration and lookup; direct-hosted modern SMB does not require it.

  38. Carte 38

    Question

    587/TCP — which email role?

    Réponse

    SMTP message submission. Mail clients normally submit outgoing mail to a submission server there, often with STARTTLS; server relay remains on TCP 25.

  39. Carte 39

    Question

    389/TCP — which directory protocol?

    Réponse

    LDAP. Ordinary connection-oriented LDAP commonly uses TCP 389; IANA also registers UDP 389 for connectionless LDAP.

  40. Carte 40

    Question

    L2TP — common port and transport?

    Réponse

    UDP 1701. L2TP carries tunnel control and data but does not provide encryption by itself; deployments often pair it with IPsec.

  41. Carte 41

    Question

    138/UDP — which NetBIOS service?

    Réponse

    NetBIOS Datagram Service. It carries connectionless NetBIOS datagrams, historically used in NetBIOS over TCP/IP environments.

  42. Carte 42

    Question

    IMAPS — default port and transport?

    Réponse

    TCP 993. It starts IMAP with an immediate TLS handshake for encrypted mail access.

  43. Carte 43

    Question

    636/TCP — which directory-service convention?

    Réponse

    LDAPS, the commonly used implicit-TLS port for LDAP. LDAP can also negotiate TLS on TCP 389.

  44. Carte 44

    Question

    1723/TCP — which VPN control protocol?

    Réponse

    PPTP control. PPTP uses TCP 1723 for control, while tunneled PPP data travels in GRE—not on TCP or UDP port 47.

  45. Carte 45

    Question

    NetBIOS Session Service — common port and transport?

    Réponse

    TCP 139. It provides connection-oriented NetBIOS sessions and historically carried SMB before direct-hosted SMB on TCP 445.

  46. Carte 46

    Question

    995/TCP — which mail-access service?

    Réponse

    POP3S. It starts POP3 with an immediate TLS handshake for encrypted mail retrieval.

  47. Carte 47

    Question

    RADIUS authentication and authorization — standard port and transport?

    Réponse

    UDP 1812. RADIUS accounting normally uses the separate UDP port 1813.

  48. Carte 48

    Question

    IPsec NAT Traversal — port and transport?

    Réponse

    UDP 4500. It carries IKE and UDP-encapsulated ESP when NAT traversal is in use.

  49. Carte 49

    Question

    5060/UDP or 5060/TCP — which signaling protocol?

    Réponse

    SIP. It commonly uses UDP or TCP 5060 for session signaling; SIP over TLS conventionally uses TCP 5061.

  50. Carte 50

    Question

    Which common dedicated ports distinguish plaintext or STARTTLS-capable services from implicit-TLS variants?

    Réponse

    HTTP 80 ↔ HTTPS 443; IMAP 143 ↔ IMAPS 993; POP3 110 ↔ POP3S 995; LDAP 389 ↔ LDAPS 636. A port alone does not prove that TLS is configured correctly.

  51. Carte 51

    Question

    22/TCP — which secure remote-access service?

    Réponse

    SSH. It supports encrypted remote login, command execution, tunneling, and file-transfer tools such as SFTP.

  52. Carte 52

    Question

    DNS — registered port and required general-purpose transports?

    Réponse

    Port 53 over UDP and TCP. Most ordinary queries start with UDP, while TCP is required for full implementations and used for zone transfers and other larger exchanges.

  53. Carte 53

    Question

    25/TCP — which email function?

    Réponse

    SMTP mail relay and delivery between servers. End-user clients normally submit new mail on TCP 587 or TCP 465 instead.

  54. Carte 54

    Question

    80/TCP — which conventional web service?

    Réponse

    HTTP without TLS. It is the conventional port for HTTP/1.1 and HTTP/2, although servers can listen elsewhere.

  55. Carte 55

    Question

    DHCPv4 server endpoint — port and transport?

    Réponse

    UDP 67. DHCPv4 clients direct server-bound messages to that port.

  56. Carte 56

    Question

    FTP control — server port and transport?

    Réponse

    TCP 21. Commands and replies use the persistent control connection; data travels on a separate connection.

  57. Carte 57

    Question

    161/UDP — which network-management traffic?

    Réponse

    SNMP requests and responses. Managed agents commonly listen on UDP 161 for manager queries.

  58. Carte 58

    Question

    Microsoft SQL Server default instance — default port and transport?

    Réponse

    TCP 1433. Named instances may use dynamic or custom ports, with SQL Server Browser commonly using UDP 1434 for discovery.

  59. Carte 59

    Question

    Telnet — conventional port and transport?

    Réponse

    TCP 23. Telnet carries terminal traffic in plaintext, so SSH is the usual secure replacement.

  60. Carte 60

    Question

    123/UDP — which time service?

    Réponse

    NTP. Network Time Protocol commonly synchronizes clocks over UDP 123.

  61. Carte 61

    Question

    110/TCP — which mail-access protocol?

    Réponse

    POP3. It downloads or retrieves mail from a server; implicit TLS uses TCP 995.

  62. Carte 62

    Question

    HTTPS — common port and transports?

    Réponse

    Port 443: TCP for HTTP/1.1 and HTTP/2 over TLS, and UDP for HTTP/3 over QUIC.

  63. Carte 63

    Question

    68/UDP — which DHCPv4 endpoint?

    Réponse

    The DHCPv4 client endpoint. Servers direct client-bound DHCP messages to UDP 68.

  64. Carte 64

    Question

    TFTP — initial request port and transport?

    Réponse

    UDP 69. Only the initial request targets 69; the server chooses another UDP transfer identifier for the data exchange.

  65. Carte 65

    Question

    SNMP traps and other notifications — common receiver port and transport?

    Réponse

    UDP 162. SNMP notification receivers commonly listen there.

  66. Carte 66

    Question

    3306/TCP — which database protocol?

    Réponse

    The classic MySQL protocol. TCP 3306 is its default client-server port and is configurable.

  67. Carte 67

    Question

    RDP — standard port and transports?

    Réponse

    TCP and UDP 3389. Microsoft Remote Desktop uses them by default, though administrators can change the listening port.

  68. Carte 68

    Question

    514/UDP — which logging protocol?

    Réponse

    Syslog over UDP. It is a conventional lightweight transport without delivery guarantees; secure syslog commonly uses another transport and port.

  69. Carte 69

    Question

    143/TCP — which mail-access protocol?

    Réponse

    IMAP. It manages mail on the server; implicit TLS uses TCP 993.

  70. Carte 70

    Question

    Direct-hosted SMB — common server port and transport?

    Réponse

    TCP 445. It carries SMB directly over TCP without the legacy NetBIOS Session Service on TCP 139.

  71. Carte 71

    Question

    Kerberos KDC traffic — port and transports?

    Réponse

    UDP and TCP 88. Conforming clients and Key Distribution Centers support both, with TCP available for larger exchanges.

  72. Carte 72

    Question

    20/TCP — which FTP role?

    Réponse

    The server side of FTP's default active-mode data connection. Passive mode negotiates a different server port.

  73. Carte 73

    Question

    179/TCP — which routing protocol?

    Réponse

    BGP. Border Gateway Protocol peers use a TCP session to exchange routing information.

  74. Carte 74

    Question

    PostgreSQL — customary default port and transport?

    Réponse

    TCP 5432. PostgreSQL servers normally use it unless configured or compiled with another default.

  75. Carte 75

    Question

    500/UDP — which IPsec setup protocol?

    Réponse

    IKE, the Internet Key Exchange protocol. It negotiates IPsec security associations and commonly moves to UDP 4500 when NAT traversal is used.

  76. Carte 76

    Question

    137/UDP — which NetBIOS service?

    Réponse

    NetBIOS Name Service. It handles name registration and lookup in legacy NetBIOS over TCP/IP environments.

  77. Carte 77

    Question

    SMTP message submission — normal port and transport?

    Réponse

    TCP 587. It separates authenticated client submission from server-to-server SMTP relay on TCP 25; STARTTLS is commonly used.

  78. Carte 78

    Question

    LDAP — conventional connection-oriented port and transport?

    Réponse

    TCP 389. Connectionless LDAP can use UDP 389, and implicit-TLS LDAP commonly uses TCP 636.

  79. Carte 79

    Question

    1701/UDP — which tunneling protocol?

    Réponse

    L2TP. It tunnels Layer 2 traffic but needs a separate security layer such as IPsec when confidentiality is required.

  80. Carte 80

    Question

    NetBIOS Datagram Service — common port and transport?

    Réponse

    UDP 138. It provides connectionless NetBIOS datagram delivery.

  81. Carte 81

    Question

    993/TCP — which mail-access service?

    Réponse

    IMAPS. It begins IMAP with implicit TLS for encrypted access to mail stored on a server.

  82. Carte 82

    Question

    LDAPS — commonly used implicit-TLS port and transport?

    Réponse

    TCP 636. LDAP can instead use TCP 389 and negotiate TLS with StartTLS.

  83. Carte 83

    Question

    PPTP control — port and transport?

    Réponse

    TCP 1723. The control channel uses that port; PPP payloads travel through GRE, which is IP protocol 47 rather than port 47.

  84. Carte 84

    Question

    139/TCP — which NetBIOS service?

    Réponse

    NetBIOS Session Service. It historically carried SMB sessions; direct-hosted SMB commonly uses TCP 445 instead.

  85. Carte 85

    Question

    POP3S — default port and transport?

    Réponse

    TCP 995. It uses implicit TLS for encrypted POP3 mail retrieval.

  86. Carte 86

    Question

    1812/UDP — which AAA service?

    Réponse

    RADIUS authentication and authorization. RADIUS accounting normally uses UDP 1813.

  87. Carte 87

    Question

    4500/UDP — which IPsec function?

    Réponse

    IPsec NAT Traversal. It carries IKE and UDP-encapsulated ESP across network address translation.

  88. Carte 88

    Question

    SIP signaling without implicit TLS — common port and transports?

    Réponse

    UDP or TCP 5060. SIP over TLS conventionally uses TCP 5061, and media streams use separately negotiated ports.

A central network gateway with glowing ports connected to web, mail, server, database, user, and security nodes.

88 cartes

Common Network Port Numbers Flashcards: Protocols, TCP/UDP & Uses

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