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 familar 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.

BSIG:

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