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Using linux servers on a dhcpd.conf file I can make a definition of ip ranges that the server will assign to host computers on the internal net:

subnet 10.0.0.1 netmask 255.255.255.0 {
  range 10.0.0.20 10.0.0.100;
  option subnet-mask 255.255.255.0;
}

Should subnet-mask and netmask be the same?

I understand that subnet-mask has to be more restrictive or at least the same that the netmask provided.

¿Which effect has netmask on the subnet defined?

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  • Surely the option subnet-mask line is redundant if it's only setting it to the same as the earlier declaration?
    – steve
    Commented Apr 21, 2019 at 9:01

1 Answer 1

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Not always. The parameters that start with the keyword option are referred to as options. These options control DHCP options; whereas, parameters configure values that are not optional or control how the DHCP server behaves. 

subnet 10.0.0.1 netmask 255.255.255.252 {
   range 10.0.0.1 10.0.0.2;
   option subnet-mask 255.255.255.0;
}

the above code will give your clients, an ip address start from 10.0.0.1 to 10.0.0.2 but the subnet mask on your clients will be 255.255.255.0

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  • So if both definitions are valid ones I need to be carefull to make masks coherent so i don't put ips out of scope
    – Antonio E.
    Commented Apr 24, 2019 at 13:15
  • yes becarefull with that. if you find out my answer was helpful you can accept my answer as correct answer and give me a vote up so both of us will get reputation. thaks
    – Rasool Ziafaty
    Commented Apr 24, 2019 at 14:55
  • I'll do, i'm just waiting a 2nd answer wich would be complementary. My votes are not allowed yet because of rep but you'll see the vote when I reach.
    – Antonio E.
    Commented Apr 24, 2019 at 15:00

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