Console, aux, and vty. Are they all TTY?

When I issue "show line", it lists all hardware ports. Go by the output, it seems to me CTY, AUX, and VTY are just different types of TTY. The TTY number goes to 21, with 2 to 4 missing. However, when I issue "show line tty ?", it says only 1 to 4 are allowed. What if I want to look tty 21 from the "show line" list?

R3#show line
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
* 0 CTY - - - - - 0 3 0/0 -
5 AUX 9600/9600 - - - - - 0 0 0/0 -
6 VTY - - - - - 0 0 0/0 -
7 VTY - - - - - 0 0 0/0 -
8 VTY - - - - - 0 0 0/0 -
9 VTY - - - - - 0 0 0/0 -
10 VTY - - - - - 0 0 0/0 -
11 VTY - - - - - 0 0 0/0 -
12 VTY - - - - - 0 0 0/0 -
13 VTY - - - - - 0 0 0/0 -
14 VTY - - - - - 0 0 0/0 -
15 VTY - - - - - 0 0 0/0 -
16 VTY - - - - - 0 0 0/0 -
17 VTY - - - - - 0 0 0/0 -
18 VTY - - - - - 0 0 0/0 -
19 VTY - - - - - 0 0 0/0 -
20 VTY - - - - - 0 0 0/0 -
21 VTY - - - - - 0 0 0/0 -

Line(s) not in async mode -or- with no hardware support:
1-4

R3#
R3#show line tty ?
<1-4> First Line range

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Comments

instant000

It's slightly confusing, because of how the IOS is based on 'NIX. If you're familiar with that, then you can remember what the Tty is referring to, see here:

http://en.wikipedia.org/wiki/Teleprinter

Of course, by also calling something "tty" it just adds a layer of ambiguity, as they use the term "Tty" and then the term "tty". Note that one uses the Big "T" and another uses the little "t"

This explains what "line" is.

Cisco IOS Terminal Services Command*Reference, Release*12.2 - Commands LI through SH* [Cisco IOS Software Releases 12.2 Mainline] - Cisco Systems

This explains "show line"

Cisco IOS Terminal Services Command*Reference, Release*12.2 - Commands LI through SH* [Cisco IOS Software Releases 12.2 Mainline] - Cisco Systems

So, based on your output, the column labeled "tty" is only referring to the line number.

Also, if you wanted to look at vty 21, you could use this syntax:
show line vty 21

EDIT: While trying to clarify this answer, I still couldn't quite explain TTY.

This is the best explanation that I've found so far:

http://tcpmag.com/international/article.asp?EditorialsID=274

workfrom925

instant000 wrote: »

Also, if you wanted to look at vty 21, you could use this syntax:
show line vty 21

Thanks for your effort. The last link explains them quite well.

Also, "show line vty 21" doesn't work. I think the 21 port is actually vty 15.

----

R3#show line vty 21
^
% Invalid input detected at '^' marker.

R3#show line vty ?
<0-15> First Line range

R3#show line vty 15
Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int
21 VTY - - - - - 0 0 0/0 -

Line 21, Location: "", Type: ""
Length: 24 lines, Width: 80 columns
Baud rate (TX/RX) is 9600/9600
Status: No Exit Banner