Command:

compress


Mode:

Router(config-if)#


Syntax:

compress [predictor | stac | mppc [ignore-pfc]]

no compress [predictor | stac | mppc [ignore-pfc]]

 

Syntax Description:

predictor

(Optional) Specifies a predictor compression algorithm will be used.

stac

(Optional) Specifies a Stacker (LZS) compression algorithm will be used.

mppc

(Optional) Specifies the MPPC compression algorithm will be used.

ignore-pfc

(Optional) Specifies the protocol field compression flag negotiated through LCP will be ignored.

 

Command Description:

To configure software compression for Point-to-Point Protocol (PPP) encapsulation, use the compress interface configuration command. To disable compression, use the no form of this command.

Usage Guidelines:

End-point devices must be configured to use the same compression method (predictor, Stacker or MPPC).

Compression reduces the size of frames via lossless data compression. The compression algorithm used is a predictor algorithm (the RAND compression algorithm), which uses a compression dictionary to predict what the next character in the frame will be.

PPP encapsulation supports both predictor and Stacker compression algorithms.

MPPC Compression

The compress command using the mppc and ignore-pfc options support compression between Cisco routers, access servers, and Microsoft clients such as Windows 95 and Windows NT. MPPC implements an LZ based compression algorithm that uses a compression dictionary to compress PPP packets. The ignore-pfc keyword instructs the router to ignore the protocol field compression flag negotiated by LCP. For example, the uncompressed standard protocol field value for IP is 0x0021 and 0x21 when compression is enabled. When the ignore-pfc option is enabled, the router will continue to use the uncompressed value (0x0021). Using the ignore-pfc option is helpful for some asynchronous driver devices which use an uncompressed protocol field (0x0021), even though the pfc is negotiated between peers. If protocol rejects are displayed when the debug ppp negotiation command is enabled, setting the ignore-pfc option may remedy the problem.

System Performance

Compression is accomplished through software and may significantly affect system performance. We recommend that you disable compression if CPU load exceeds 65 percent. To display the CPU load, use the show process cpu EXEC command.

You should never enable compression for connections to a public data network.

If the majority of your traffic is already compressed files, we recommend that you not use compression. If the files are already compressed, the additional processing time spent in unsuccessfully attempting to compress them again will slow system performance.


Example:

 

The following example enables predictor compression on serial interface 0:

  Router(config)#interface serial 0

  Router(config-if)#encapsulation ppp

  Router(config-if)#compress predictor

    

The following example configures BRI interface 0 to perform MPPC:

  Router(config)#interface BRI 0

  Router(config-if)#ip unnumbered ethernet 0

  Router(config-if)#encapsulation ppp

  Router(config-if)#isdn spid1 5551234

  Router(config-if)#dialer map ip 172.21.71.74 5551234

  Router(config-if)#dialer-group 1

  Router(config-if)#compress mppc

    

The following example configures asynchronous interface 1 to implement MPPC and ignore the protocol field compression flag negotiated by LCP:

  Router(config)#interface async 1

  Router(config-if)#ip unnumbered ethernet 0

  Router(config-if)#encapsulation ppp

  Router(config-if)#default routing

  Router(config-if)#async dynamic routing

  Router(config-if)#async mode interactive

  Router(config-if)#peer default ip address 172.21.71.74

  Router(config-if)#compress mppc ignore-pfc


Misconceptions:

 

None


Related Commands:

 

encapsulation ppp

 


� Cisco Systems, Inc. 2001, 2002, 2003
World Wide Education

Converted from CHM to HTML with chm2web Pro 2.85 (unicode)