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.
Um þennan stokk
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.
Spjöld í þessum stokki
Spjald 1
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What does a transport-layer port number identify?
Svar
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.
Spjald 2
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Are TCP port 53 and UDP port 53 the same port?
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No. TCP and UDP have independent 16-bit port namespaces, so 53/TCP and 53/UDP are separate transport endpoints.
Spjald 3
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What is the IANA System Port range?
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0–1023. These are also called Well-Known Ports and are assigned by IANA under the stricter System Port procedures.
Spjald 4
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What is the IANA User Port range?
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1024–49151. These are also called Registered Ports and may be assigned by IANA to services.
Spjald 5
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What is the IANA Dynamic or Private Port range?
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49152–65535. IANA does not assign ports in this range; systems commonly use it for temporary or private endpoints.
Spjald 6
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Does an IANA port assignment prove what observed traffic is—or that it is safe?
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No. A registration is a naming convention, not traffic identification, authorization, or a security verdict. Verify the actual protocol and context.
Spjald 7
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Must a service use its registered or conventional port?
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No. Administrators and applications can choose another port, negotiate one dynamically, or discover it through mechanisms such as DNS SRV records.
Spjald 8
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What port roles are typical in a client-server connection?
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The server usually listens on a known destination port, while the client uses a temporary source port. Either side can be configured differently.
Spjald 9
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SSH and SFTP — common server port and transport?
Svar
TCP 22. SSH provides encrypted remote access, and SFTP normally runs as a subsystem inside the same SSH connection.
Spjald 10
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53/UDP or 53/TCP — which service?
Svar
DNS. Routine queries often use UDP, while full DNS implementations also support TCP; zone transfers use TCP.
Spjald 11
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SMTP relay between mail servers — common port and transport?
Svar
TCP 25. SMTP uses it for server-to-server mail transfer; user mail submission normally uses port 587 or implicit TLS on 465.
Spjald 12
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HTTP without TLS — conventional port and transport?
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TCP 80 for conventional HTTP/1.1 and HTTP/2 connections. The service can be configured on another port.
Spjald 13
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67/UDP — which DHCPv4 endpoint?
Svar
The DHCPv4 server endpoint. Clients send server-directed DHCP messages to UDP port 67.
Spjald 14
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21/TCP — which service and channel?
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FTP control. It carries commands and replies; file data uses a separate connection.
Spjald 15
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SNMP requests and responses — common agent port and transport?
Svar
UDP 161. Managers commonly send queries to an SNMP agent there; other SNMP transports exist.
Spjald 16
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1433/TCP — which database service?
Svar
Microsoft SQL Server's default instance. TCP 1433 is the default Database Engine port, but named or custom instances may use another port.
Spjald 17
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23/TCP — which remote-access protocol?
Svar
Telnet. It provides a plaintext remote terminal session and does not protect credentials or traffic with encryption.
Spjald 18
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NTP — usual port and transport?
Svar
UDP 123. NTP normally uses UDP for time synchronization; IANA also has a TCP 123 registration, but that is not the usual NTP transport.
Spjald 19
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Why must a general-purpose DNS implementation support both UDP and TCP?
Svar
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.
Spjald 20
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POP3 — conventional port and transport?
Svar
TCP 110. POP3 retrieves mail; it can upgrade with STLS, while implicit TLS uses TCP 995.
Spjald 21
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443/TCP or 443/UDP — which web service?
Svar
HTTPS. HTTP/1.1 and HTTP/2 normally use TLS over TCP 443; HTTP/3 uses QUIC over UDP 443.
Spjald 22
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DHCPv4 client endpoint — port and transport?
Svar
UDP 68. Servers send client-directed DHCPv4 messages to port 68.
Spjald 23
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69/UDP — which file-transfer protocol?
Svar
TFTP. A client sends the initial read or write request to UDP 69; the transfer then continues with a server-selected UDP transfer identifier.
Spjald 24
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162/UDP — which network-management traffic?
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SNMP notifications, traditionally called traps. Notification receivers commonly listen on UDP 162.
Spjald 25
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MySQL classic protocol — default port and transport?
Svar
TCP 3306. It is the default for classic MySQL client-server connections and can be reconfigured.
Spjald 26
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How do FTP control, active-mode data, and passive-mode data ports differ?
Svar
Control uses TCP 21. The server side of the default active-mode data connection uses TCP 20, while passive mode negotiates another server port.
Spjald 27
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3389/TCP or 3389/UDP — which remote-desktop service?
Svar
Microsoft Remote Desktop Protocol (RDP). TCP and UDP 3389 are the standard defaults, and the listening port can be changed.
Spjald 28
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Syslog's conventional UDP transport — port?
Svar
UDP 514. Classic syslog over UDP has no delivery guarantee; TCP 514 is registered to the shell service, not syslog.
Spjald 29
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How do DHCPv4 server and client ports pair up?
Svar
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.
Spjald 30
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IMAP — conventional port and transport?
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TCP 143. IMAP accesses and manages mail on a server; implicit TLS uses TCP 993.
Spjald 31
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445/TCP — which file-sharing service?
Svar
Direct-hosted SMB. Modern SMB servers commonly listen on TCP 445 without the older NetBIOS session layer.
Spjald 32
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88/UDP or 88/TCP — which authentication protocol?
Svar
Kerberos. Clients and Key Distribution Centers support both transports; TCP also handles requests or replies too large for UDP.
Spjald 33
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FTP's default active-mode data connection — server-side port and transport?
Svar
TCP 20. This is the server's default source port for active-mode data; passive FTP negotiates another server port.
Spjald 34
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BGP — standard operational port and transport?
Svar
TCP 179. RFC 4271 defines BGP peer sessions over TCP; IANA separately retains a UDP 179 registry entry.
Spjald 35
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5432/TCP — which database service?
Svar
PostgreSQL. TCP 5432 is the customary default server port, but an installation can choose another port.
Spjald 36
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IKE for IPsec — initial port and transport?
Svar
UDP 500. IKE normally begins there; NAT traversal commonly moves subsequent IKE and encapsulated ESP traffic to UDP 4500.
Spjald 37
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NetBIOS Name Service — common port and transport?
Svar
UDP 137. It supports NetBIOS name registration and lookup; direct-hosted modern SMB does not require it.
Spjald 38
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587/TCP — which email role?
Svar
SMTP message submission. Mail clients normally submit outgoing mail to a submission server there, often with STARTTLS; server relay remains on TCP 25.
Spjald 39
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389/TCP — which directory protocol?
Svar
LDAP. Ordinary connection-oriented LDAP commonly uses TCP 389; IANA also registers UDP 389 for connectionless LDAP.
Spjald 40
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L2TP — common port and transport?
Svar
UDP 1701. L2TP carries tunnel control and data but does not provide encryption by itself; deployments often pair it with IPsec.
Spjald 41
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138/UDP — which NetBIOS service?
Svar
NetBIOS Datagram Service. It carries connectionless NetBIOS datagrams, historically used in NetBIOS over TCP/IP environments.
Spjald 42
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IMAPS — default port and transport?
Svar
TCP 993. It starts IMAP with an immediate TLS handshake for encrypted mail access.
Spjald 43
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636/TCP — which directory-service convention?
Svar
LDAPS, the commonly used implicit-TLS port for LDAP. LDAP can also negotiate TLS on TCP 389.
Spjald 44
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1723/TCP — which VPN control protocol?
Svar
PPTP control. PPTP uses TCP 1723 for control, while tunneled PPP data travels in GRE—not on TCP or UDP port 47.
Spjald 45
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NetBIOS Session Service — common port and transport?
Svar
TCP 139. It provides connection-oriented NetBIOS sessions and historically carried SMB before direct-hosted SMB on TCP 445.
Spjald 46
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995/TCP — which mail-access service?
Svar
POP3S. It starts POP3 with an immediate TLS handshake for encrypted mail retrieval.
Spjald 47
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RADIUS authentication and authorization — standard port and transport?
Svar
UDP 1812. RADIUS accounting normally uses the separate UDP port 1813.
Spjald 48
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IPsec NAT Traversal — port and transport?
Svar
UDP 4500. It carries IKE and UDP-encapsulated ESP when NAT traversal is in use.
Spjald 49
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5060/UDP or 5060/TCP — which signaling protocol?
Svar
SIP. It commonly uses UDP or TCP 5060 for session signaling; SIP over TLS conventionally uses TCP 5061.
Spjald 50
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Which common dedicated ports distinguish plaintext or STARTTLS-capable services from implicit-TLS variants?
Svar
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.
Spjald 51
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22/TCP — which secure remote-access service?
Svar
SSH. It supports encrypted remote login, command execution, tunneling, and file-transfer tools such as SFTP.
Spjald 52
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DNS — registered port and required general-purpose transports?
Svar
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.
Spjald 53
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25/TCP — which email function?
Svar
SMTP mail relay and delivery between servers. End-user clients normally submit new mail on TCP 587 or TCP 465 instead.
Spjald 54
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80/TCP — which conventional web service?
Svar
HTTP without TLS. It is the conventional port for HTTP/1.1 and HTTP/2, although servers can listen elsewhere.
Spjald 55
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DHCPv4 server endpoint — port and transport?
Svar
UDP 67. DHCPv4 clients direct server-bound messages to that port.
Spjald 56
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FTP control — server port and transport?
Svar
TCP 21. Commands and replies use the persistent control connection; data travels on a separate connection.
Spjald 57
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161/UDP — which network-management traffic?
Svar
SNMP requests and responses. Managed agents commonly listen on UDP 161 for manager queries.
Spjald 58
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Microsoft SQL Server default instance — default port and transport?
Svar
TCP 1433. Named instances may use dynamic or custom ports, with SQL Server Browser commonly using UDP 1434 for discovery.
Spjald 59
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Telnet — conventional port and transport?
Svar
TCP 23. Telnet carries terminal traffic in plaintext, so SSH is the usual secure replacement.
Spjald 60
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123/UDP — which time service?
Svar
NTP. Network Time Protocol commonly synchronizes clocks over UDP 123.
Spjald 61
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110/TCP — which mail-access protocol?
Svar
POP3. It downloads or retrieves mail from a server; implicit TLS uses TCP 995.
Spjald 62
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HTTPS — common port and transports?
Svar
Port 443: TCP for HTTP/1.1 and HTTP/2 over TLS, and UDP for HTTP/3 over QUIC.
Spjald 63
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68/UDP — which DHCPv4 endpoint?
Svar
The DHCPv4 client endpoint. Servers direct client-bound DHCP messages to UDP 68.
Spjald 64
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TFTP — initial request port and transport?
Svar
UDP 69. Only the initial request targets 69; the server chooses another UDP transfer identifier for the data exchange.
Spjald 65
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SNMP traps and other notifications — common receiver port and transport?
Svar
UDP 162. SNMP notification receivers commonly listen there.
Spjald 66
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3306/TCP — which database protocol?
Svar
The classic MySQL protocol. TCP 3306 is its default client-server port and is configurable.
Spjald 67
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RDP — standard port and transports?
Svar
TCP and UDP 3389. Microsoft Remote Desktop uses them by default, though administrators can change the listening port.
Spjald 68
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514/UDP — which logging protocol?
Svar
Syslog over UDP. It is a conventional lightweight transport without delivery guarantees; secure syslog commonly uses another transport and port.
Spjald 69
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143/TCP — which mail-access protocol?
Svar
IMAP. It manages mail on the server; implicit TLS uses TCP 993.
Spjald 70
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Direct-hosted SMB — common server port and transport?
Svar
TCP 445. It carries SMB directly over TCP without the legacy NetBIOS Session Service on TCP 139.
Spjald 71
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Kerberos KDC traffic — port and transports?
Svar
UDP and TCP 88. Conforming clients and Key Distribution Centers support both, with TCP available for larger exchanges.
Spjald 72
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20/TCP — which FTP role?
Svar
The server side of FTP's default active-mode data connection. Passive mode negotiates a different server port.
Spjald 73
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179/TCP — which routing protocol?
Svar
BGP. Border Gateway Protocol peers use a TCP session to exchange routing information.
Spjald 74
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PostgreSQL — customary default port and transport?
Svar
TCP 5432. PostgreSQL servers normally use it unless configured or compiled with another default.
Spjald 75
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500/UDP — which IPsec setup protocol?
Svar
IKE, the Internet Key Exchange protocol. It negotiates IPsec security associations and commonly moves to UDP 4500 when NAT traversal is used.
Spjald 76
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137/UDP — which NetBIOS service?
Svar
NetBIOS Name Service. It handles name registration and lookup in legacy NetBIOS over TCP/IP environments.
Spjald 77
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SMTP message submission — normal port and transport?
Svar
TCP 587. It separates authenticated client submission from server-to-server SMTP relay on TCP 25; STARTTLS is commonly used.
Spjald 78
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LDAP — conventional connection-oriented port and transport?
Svar
TCP 389. Connectionless LDAP can use UDP 389, and implicit-TLS LDAP commonly uses TCP 636.
Spjald 79
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1701/UDP — which tunneling protocol?
Svar
L2TP. It tunnels Layer 2 traffic but needs a separate security layer such as IPsec when confidentiality is required.
Spjald 80
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NetBIOS Datagram Service — common port and transport?
Svar
UDP 138. It provides connectionless NetBIOS datagram delivery.
Spjald 81
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993/TCP — which mail-access service?
Svar
IMAPS. It begins IMAP with implicit TLS for encrypted access to mail stored on a server.
Spjald 82
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LDAPS — commonly used implicit-TLS port and transport?
Svar
TCP 636. LDAP can instead use TCP 389 and negotiate TLS with StartTLS.
Spjald 83
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PPTP control — port and transport?
Svar
TCP 1723. The control channel uses that port; PPP payloads travel through GRE, which is IP protocol 47 rather than port 47.
Spjald 84
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139/TCP — which NetBIOS service?
Svar
NetBIOS Session Service. It historically carried SMB sessions; direct-hosted SMB commonly uses TCP 445 instead.
Spjald 85
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POP3S — default port and transport?
Svar
TCP 995. It uses implicit TLS for encrypted POP3 mail retrieval.
Spjald 86
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1812/UDP — which AAA service?
Svar
RADIUS authentication and authorization. RADIUS accounting normally uses UDP 1813.
Spjald 87
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4500/UDP — which IPsec function?
Svar
IPsec NAT Traversal. It carries IKE and UDP-encapsulated ESP across network address translation.
Spjald 88
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SIP signaling without implicit TLS — common port and transports?
Svar
UDP or TCP 5060. SIP over TLS conventionally uses TCP 5061, and media streams use separately negotiated ports.
88 spjöld
Common Network Port Numbers Flashcards: Protocols, TCP/UDP & Uses
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