what is the meaning of netmask in pcap_compile() API?

["WANG Yong"<yongw () 21cn com>]

Hi All:

I am using libpcap to receive ISO8473 CLNP/802.2 LLC1 packets from network interface and I need to set some filter 
using pcap_compile() API. This API has a parameter named netmask. I suppose this is only useful when doing jobs related 
to TCP/IP, so in my case i can safely ignore it and set it any value.

Anybody who can explain the usage of this parameter? Many thanks!
 
                                 
　　　　　　　　WANG Yong
　　　　　　　　yongw () 21cn com
　　　　　　　　　　2003-11-29

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