Doing this enables us to use a mediation to apply optional messaging processing, such as filtering the message content or routing to a different destination, just to name a few.
The optional match section of the iptables command specifies the characteristics that a packet should have to match the rule, such as source and destination address, protocol, etc.
iptables 命令的可选 match 部分指定信息包与规则匹配所应具有的特征（如源和目的地地址、协议等）。
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Life is like a curve, starting point and the destination are not optional, but countless opportunities are between starting point and destination.