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plko345
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tcpdump net 用法疑问

  •  
      plko345 2020-08-05 16:59:46 +08:00 1994 次点击
    这是一个创建于 1964 天前的主题,其中的信息可能已经有所发展或是发生改变。
    # 正常开始捕获 tcpdump net 65.192.0.0/10 # 1 # 报错: tcpdump: non-network bits set in "10.44.0.0/10" tcpdump net 10.44.0.0/10 # 2 # 正常开始捕获 tcpdump net 10.44.0.0/14 # 3, 14 以上正常捕获 

    找到网上的说法是:

    This is because the apparent intent of your rule is to exclude traffic from your local network, and the correct way to specify a network address is to specify the network's lowest IP address (which is called the network address) / netmask. If you specify any address other than the lowest address in the range for a network with a netmask of $myNetworkBytes, then you will get the error message:

    man page 中的解释:

    True if the IPv4/v6 address matches net with a netmask len bits wide. May be qualified with src or dst.

    OK, 然后我还是没太明白(哭~), 有大佬解释下吗? 1 可以, 2 却不行, 3 为什么 14 就可以了, 不应该是 16 之后才可以吗?

    5 条回复    2020-08-05 21:22:16 +08:00
    hatebugs
        1
    hatebugs  
       2020-08-05 17:32:33 +08:00 via Android   1
    44-= 00101100 14=8+6 。 老老实实先算好再用 net
    plko345
        3
    plko345  
    OP
       2020-08-05 18:23:22 +08:00
    @hatebugs 谢谢, 那为什么 tcpdump 不支持 10.44.0.0/10 这种写法呢? 这种不就等于 10.0.0.0/10 吗?
    gefranks
        4
    gefranks  
       2020-08-05 20:57:39 +08:00   1
    10.44.0.0/10 还真不等于 10.0.0.0/10 在我看来会产生 4 个子网 10.0.0.0/10, 10.64.0.0/10, 10.128.0.0/10, 10.192.0.0/10
    这个 44 是落在第一个子网里的, 而写目标网络的时候是按一块一块来写的.
    写主机地址的时候 10.44.0.0/10 是可以的,但是网络地址是不对的
    plko345
        5
    plko345  
    OP
       2020-08-05 21:22:16 +08:00
    @gefranks 谢谢, 大致明白了, 我再去复习下
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