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Transport Layer (Layer 4) - Reserved TCP and UDP Port Numbers

Port Keyword Description
0 - Reserved
1-4 - Unassigned
5 rje Remote job entry
7 echo Echo
9 discard Discard
11 users Active users
13 daytime Day
15 netstat Who is up or netstat
17 quote Quote of the day
19 chargen Character generator
20 ftp-data File Transfer Protocol (data)
21 ftp File Transfer Protocol
23 telnet Terminal connection
25 smtp Simple Mail Transfer Protocol
37 time Time of day
39 rlp Resource Location Protocol
42 nameserver Hostname server
43 nickname WhoIs
53 domain Domain Name Server
67 bootps Bootstrap protocol server
68 bootpc Bootstrap protocol client
69 tftp Trivial File Transfer Protocol
75 - Any private dial-out service
77 - Any private RJE service
79 finger Finger
80 http Hypertext Transfer Protocol
123 ntp Network time protocol
133-159 - Unassigned
160-223 - Reserved
224-241 - Unassigned
242-255 - Unassigned

You must be familiar with these Transport Layer (4) Port assignments. For a complete list -- check out this superb site.

Also -- it would be a smart thing to memorize this list:

  • 0 to 254 - used for public applications.

  • 255 to 1023 - assigned to companies* for marketable applications.

  • 1024 and above - unregulated.

* Real Audio's rtsp (real-time streaming protocol) via port 554 is a good example.

Don't forget -- no matter what you may discover out there in cyberspace regarding transport layer ports -- focus on how they are assigned within Cisco's world of internetworking.

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