Why are there negative values in the %Bytes Saved column in the output of "compression show"?
The %Bytes Saved column in the output of compression show shows negative values for some traffic classes:
PacketShaper# comp show 188.8.131.52
Decompressors Type %Bytes Saved
Negative compression gains can result when the original packets are not compressible. The post compression IPCOMP packet ends up being larger than the pre-compressed packet. In order for positive compression gains to take place, the original packet must be compressed by a greater number of bytes than are added by the additional IPCOMP packet header.
The compression show output is a snapshot showing the compression gains for traffic types over the last eight packets compressed. For a more realistic view of compression gains, use the compression reports for those classes to measure compression gains over a longer period of time.
If class compression reports consistently show low or negative compression gains, compression for a class can be disabled using the command:
class compress <tclass> off
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