Student here. Could someone please explain to me the difference between these two? I'm using a serial connection for this. Does the latter refer to one individual serial terminal session? Why would one use line configuration mode over global? Thanks, I appreciate any help.
2 Answers
Global configuration mode is for configuring global parameters. This is the default mode when you enter configuration mode.
Some commands will cause you to enter a more specific configuration mode. Line configuration mode (similar to interface configuration mode) is entered when you specify a line to configure. Line configuration mode is then where you enter configuration appropriate to that specific line.
When you are in a specific configuration mode, if you prompt for help (i.e. type "?") you will only be shown commands that are relevant to that configuration mode rather than commands that are relevant in global configuration mode.
Here is the output of line configuration mode from one of my test switches:
Test(config-line)#?
Line configuration commands:
access-class Filter connections based on an IP access list
accounting Accounting parameters
authorization Authorization parameters
autocommand Automatically execute an EXEC command
autocommand-options Autocommand options
data-character-bits Size of characters being handled
databits Set number of data bits per character
default Set a command to its defaults
domain-lookup Enable domain lookups in show commands
editing Enable command line editing
escape-character Change the current line's escape character
exec Configure EXEC
exec-banner Enable the display of the EXEC banner
exec-character-bits Size of characters to the command exec
exec-timeout Set the EXEC timeout
exit Exit from line configuration mode
flowcontrol Set the flow control
full-help Provide help to unprivileged user
help Description of the interactive help system
history Enable and control the command history function
international Enable international 8-bit character support
ip IP options
length Set number of lines on a screen
location Enter terminal location description
logging Modify message logging facilities
login Enable password checking
modem Configure the Modem Control Lines
monitor Copy debug output to the current terminal line
motd-banner Enable the display of the MOTD banner
no Negate a command or set its defaults
notify Inform users of output from concurrent sessions
padding Set padding for a specified output character
parity Set terminal parity
password Set a password
privilege Change privilege level for line
refuse-message Define a refuse banner
rotary Add line to a rotary group
rxspeed Set the receive speed
session-timeout Set interval for closing connection when there is no input traffic
special-character-bits Size of the escape (and other special) characters
speed Set the transmit and receive speeds
start-character Define the start character
stop-character Define the stop character
stopbits Set async line stop bits
terminal-type Set the terminal type
timeout Timeouts for the line
transport Define transport protocols for line
txspeed Set the transmit speeds
vacant-message Define a vacant banner
width Set width of the display terminal
Notice that while some of the commands are the same (or similar), many of the global configuration mode commands you might expect are not present, such as aaa
, boot
or cdp
. This last would be present in interface configuration mode, but there is no CDP on the console so it is not present.
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Thank you. Distilling further, I guess my real question is what does "line" mean in this regard? I know serial console sessions have only 1 line, yet telnet can support 16. What is the point of defining multiple sessions and how does it affect the configuration state of the switch? Mar 22, 2016 at 22:26
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A line can only support one active connection/session at a time. So console only has one line because you can't make two connections to a single console port. VTY lines (or virtual TTYs) are used for things like telnet or SSH and can often support multiple connections at the same time. This is why most Cisco devices support at least 5 VTYs (modern devices support at least 16). While often all VTYs are configured the same, this does not need to be the case. For instance, you could "reserve" some VTYs by placing higher restrictions on them (i.e. only allow the "super-admin" computers by ACL).– YLearnMar 23, 2016 at 20:05
It doesn't matter if you are connected to the router via console, telnet, SSH, etc., you configure a specific feature in the mode for that specific feature.
If you need to configure global commands, you do that in global configuration.
If you are configuring interfaces, you do that in interface configuration.
If you are configuring lines, you do that in line configuration.
If you are configuring a routing protocol, you do that in router configuration.
Etc.