Why does one port show two protocols?

Some services listen on both TCP and UDP. DNS uses 53 for both: UDP for ordinary queries and TCP for zone transfers and large responses.

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What runs on port N?

Type a port number, a service name or a protocol. See the job the service does, not just the number, because the exam asks what to open, block or investigate.

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22TCPSSHSecure Shell remote administration; also SCP and SFTP
53TCP/UDPDNSDomain Name System lookups (UDP) and zone transfers (TCP)
80TCPHTTPUnencrypted web traffic
443TCPHTTPSHTTP over TLS
3389TCP/UDPRDPRemote Desktop Protocol; gatekeep from the internet

Showing 5 of 44 entries. Port numbers and services are checked against the published objectives and IANA assignments. The list is a study aid, not a live scan.

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Questions

Read the symptom, name the service, then recall the port and protocol. A blocked 53/UDP usually means name resolution fails while ping to an IP still works. A blocked 3389/TCP means remote desktop fails. The number alone is less useful than the service plus its direction.

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