The service compress-config command causes the configuration to be saved in a compressed form in NVRAM. When the router loads, the configuration is decompressed into RAM.
To adjust the size of the buffer allocated for the running configuration in RAM, issue the boot buffersize command. By default, the buffer size is the size of NVRAM. For example, if a router's NVRAM size is 32 k, but the running configuration is 40 k before it is compressed to fit in NVRAM, the buffer size should be increased to at least 40 k. The command is boot buffersize 40000. This value may be larger to accomodate additions to the configuration.
Note: The boot buffersize command is only needed in Cisco IOS software versions 12.0 and earlier. From Cisco IOS ver 12.1 the command - service compress-config will solve the NVRAM size issue and the user is not required to configure the command boot buffersize.
This is an example of the service compress-config and boot buffersize commands, where the buffer size is increased to 64,000 bytes. The buffer size changes at the next reload:
Enter configuration commands, one per line. End with CNTL/Z.
3725ESW(config)#boot buffersize 64000
Compressed configuration from 2872 bytes to 1131 bytes[OK]
Using 1131 out of 57336 bytes, uncompressed size = 2872 bytes
Uncompressed configuration from 1131 bytes to 2872 bytes