ip tcp header-compression
ip tcp header-compression [on | off | passive]
no ip tcp header-compression
(Optional) Turns header compression on.
(Optional) Turns header compression off.
(Optional) On SLIP lines, prevents transmission of compressed packets until a compressed packet arrives from the asynchronous link, unless a user specifies SLIP on the command line. For PPP, this option functions the same as the on option.
To configure TCP header compression on the asynchronous link, use the ip tcp header-compression interface configuration command. To disable header compression, use the no form of this command.
Header compression data areas are initialized to handle up to 16 simultaneous TCP connections. Currently, you cannot change this number. You can only turn header compression on or off or use the passive keyword.
On lines configured for PPP encapsulation, the keywords passive and on cause the same behavior. Before attempting header compression, PPP automatically negotiates whether compression is available at each end of the connection.
There are two ways to implement header compression when the line is configured for ip tcp header-compression passive:
- The user enters the /compressed option with the slip EXEC commands to force the line into compressed mode. This overrides the passive setting and causes the interface to behave as if header compression is enabled.
- The user enters slip or slip default and the connecting system sends compressed packets to the server. The server detects the use of compression by the connecting system and automatically enters compressed mode.
If a line is configured for passive header compression and you use the slip or ppp EXEC command to enter asynchronous mode, you will see the interface is set to match the compression status used by the host at the other end of the asynchronous line.
Router>slip 10.0.0.1 Password: Entering SLIP mode. Interface IP address is 10.0.0.1, MTU is 1500 bytes Header compression will match your system.
The message "Header compression will match your system" indicates the interface is set to match the compression status used by the host at the other end of the asynchronous line. If the line was configured to have header compression on, this line would read "Header compression is On."
The following example enables Van Jacobson TCP header compression. The passive keyword prevents transmission of compressed packets until a compressed packet arrives from the IP link. Notice that asynchronous routing and dynamic addressing are also enabled.Router(config)#interface async 6 Router(config-if)#async dynamic routing Router(config-if)#async dynamic address Router(config-if)#ip tcp header-compression passive
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