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

这套卡组中的卡片

1. 卡片 1

   问题

   What does a transport-layer port number identify?

   答案

   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. 卡片 2

   问题

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

   答案

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

3. 卡片 3

   问题

   What is the IANA System Port range?

   答案

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

4. 卡片 4

   问题

   What is the IANA User Port range?

   答案

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

5. 卡片 5

   问题

   What is the IANA Dynamic or Private Port range?

   答案

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

6. 卡片 6

   问题

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

   答案

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

7. 卡片 7

   问题

   Must a service use its registered or conventional port?

   答案

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

8. 卡片 8

   问题

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

   答案

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

9. 卡片 9

   问题

   SSH and SFTP — common server port and transport?

   答案

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

10. 卡片 10

    问题

    53/UDP or 53/TCP — which service?

    答案

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

11. 卡片 11

    问题

    SMTP relay between mail servers — common port and transport?

    答案

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

12. 卡片 12

    问题

    HTTP without TLS — conventional port and transport?

    答案

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

13. 卡片 13

    问题

    67/UDP — which DHCPv4 endpoint?

    答案

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

14. 卡片 14

    问题

    21/TCP — which service and channel?

    答案

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

15. 卡片 15

    问题

    SNMP requests and responses — common agent port and transport?

    答案

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

16. 卡片 16

    问题

    1433/TCP — which database service?

    答案

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

17. 卡片 17

    问题

    23/TCP — which remote-access protocol?

    答案

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

18. 卡片 18

    问题

    NTP — usual port and transport?

    答案

    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. 卡片 19

    问题

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

    答案

    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. 卡片 20

    问题

    POP3 — conventional port and transport?

    答案

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

21. 卡片 21

    问题

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

    答案

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

22. 卡片 22

    问题

    DHCPv4 client endpoint — port and transport?

    答案

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

23. 卡片 23

    问题

    69/UDP — which file-transfer protocol?

    答案

    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. 卡片 24

    问题

    162/UDP — which network-management traffic?

    答案

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

25. 卡片 25

    问题

    MySQL classic protocol — default port and transport?

    答案

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

26. 卡片 26

    问题

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

    答案

    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. 卡片 27

    问题

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

    答案

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

28. 卡片 28

    问题

    Syslog's conventional UDP transport — port?

    答案

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

29. 卡片 29

    问题

    How do DHCPv4 server and client ports pair up?

    答案

    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. 卡片 30

    问题

    IMAP — conventional port and transport?

    答案

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

31. 卡片 31

    问题

    445/TCP — which file-sharing service?

    答案

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

32. 卡片 32

    问题

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

    答案

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

33. 卡片 33

    问题

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

    答案

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

34. 卡片 34

    问题

    BGP — standard operational port and transport?

    答案

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

35. 卡片 35

    问题

    5432/TCP — which database service?

    答案

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

36. 卡片 36

    问题

    IKE for IPsec — initial port and transport?

    答案

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

37. 卡片 37

    问题

    NetBIOS Name Service — common port and transport?

    答案

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

38. 卡片 38

    问题

    587/TCP — which email role?

    答案

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

39. 卡片 39

    问题

    389/TCP — which directory protocol?

    答案

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

40. 卡片 40

    问题

    L2TP — common port and transport?

    答案

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

41. 卡片 41

    问题

    138/UDP — which NetBIOS service?

    答案

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

42. 卡片 42

    问题

    IMAPS — default port and transport?

    答案

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

43. 卡片 43

    问题

    636/TCP — which directory-service convention?

    答案

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

44. 卡片 44

    问题

    1723/TCP — which VPN control protocol?

    答案

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

45. 卡片 45

    问题

    NetBIOS Session Service — common port and transport?

    答案

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

46. 卡片 46

    问题

    995/TCP — which mail-access service?

    答案

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

47. 卡片 47

    问题

    RADIUS authentication and authorization — standard port and transport?

    答案

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

48. 卡片 48

    问题

    IPsec NAT Traversal — port and transport?

    答案

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

49. 卡片 49

    问题

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

    答案

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

50. 卡片 50

    问题

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

    答案

    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. 卡片 51

    问题

    22/TCP — which secure remote-access service?

    答案

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

52. 卡片 52

    问题

    DNS — registered port and required general-purpose transports?

    答案

    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. 卡片 53

    问题

    25/TCP — which email function?

    答案

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

54. 卡片 54

    问题

    80/TCP — which conventional web service?

    答案

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

55. 卡片 55

    问题

    DHCPv4 server endpoint — port and transport?

    答案

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

56. 卡片 56

    问题

    FTP control — server port and transport?

    答案

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

57. 卡片 57

    问题

    161/UDP — which network-management traffic?

    答案

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

58. 卡片 58

    问题

    Microsoft SQL Server default instance — default port and transport?

    答案

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

59. 卡片 59

    问题

    Telnet — conventional port and transport?

    答案

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

60. 卡片 60

    问题

    123/UDP — which time service?

    答案

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

61. 卡片 61

    问题

    110/TCP — which mail-access protocol?

    答案

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

62. 卡片 62

    问题

    HTTPS — common port and transports?

    答案

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

63. 卡片 63

    问题

    68/UDP — which DHCPv4 endpoint?

    答案

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

64. 卡片 64

    问题

    TFTP — initial request port and transport?

    答案

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

65. 卡片 65

    问题

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

    答案

    UDP 162. SNMP notification receivers commonly listen there.

66. 卡片 66

    问题

    3306/TCP — which database protocol?

    答案

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

67. 卡片 67

    问题

    RDP — standard port and transports?

    答案

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

68. 卡片 68

    问题

    514/UDP — which logging protocol?

    答案

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

69. 卡片 69

    问题

    143/TCP — which mail-access protocol?

    答案

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

70. 卡片 70

    问题

    Direct-hosted SMB — common server port and transport?

    答案

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

71. 卡片 71

    问题

    Kerberos KDC traffic — port and transports?

    答案

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

72. 卡片 72

    问题

    20/TCP — which FTP role?

    答案

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

73. 卡片 73

    问题

    179/TCP — which routing protocol?

    答案

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

74. 卡片 74

    问题

    PostgreSQL — customary default port and transport?

    答案

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

75. 卡片 75

    问题

    500/UDP — which IPsec setup protocol?

    答案

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

76. 卡片 76

    问题

    137/UDP — which NetBIOS service?

    答案

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

77. 卡片 77

    问题

    SMTP message submission — normal port and transport?

    答案

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

78. 卡片 78

    问题

    LDAP — conventional connection-oriented port and transport?

    答案

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

79. 卡片 79

    问题

    1701/UDP — which tunneling protocol?

    答案

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

80. 卡片 80

    问题

    NetBIOS Datagram Service — common port and transport?

    答案

    UDP 138. It provides connectionless NetBIOS datagram delivery.

81. 卡片 81

    问题

    993/TCP — which mail-access service?

    答案

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

82. 卡片 82

    问题

    LDAPS — commonly used implicit-TLS port and transport?

    答案

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

83. 卡片 83

    问题

    PPTP control — port and transport?

    答案

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

84. 卡片 84

    问题

    139/TCP — which NetBIOS service?

    答案

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

85. 卡片 85

    问题

    POP3S — default port and transport?

    答案

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

86. 卡片 86

    问题

    1812/UDP — which AAA service?

    答案

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

87. 卡片 87

    问题

    4500/UDP — which IPsec function?

    答案

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

88. 卡片 88

    问题

    SIP signaling without implicit TLS — common port and transports?

    答案

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

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

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