ISC DHCP - Two subnets on one physical interface.

Discussion in 'Linux Networking' started by Dan, Jul 31, 2007.

  1. Dan

    Dan Guest

    I'm having some trouble trying to get dhcp to serve two subnets on one
    interface.
    The first is 10.0.0.0/24 which is for office workstations and
    equipment. Everyone in here is assigned a static ip via mac address.
    The second is a 'guest' network which is 10.0.10.0/24.

    I was able to get dhcp to assign the ip address for both subnets by
    making the subnet declaration 10.0.0.0/16. The problem is that there
    are other settings that need to be set like the default route, dns,
    netmask, etc.

    In my first attempt, I made a pool and set all the settings to be that
    of the guest network. I would then override those settings in the
    host declarations for the office equipment. The problem is that it
    didn't like having options such as routers,domain-name-servers, etc in
    the host declarations.

    Does anyone know how I can do this without a second NIC?

    Below is my current config.
    ################ Current Config #################
    max-lease-time 86400;
    default-lease-time 14400;
    ddns-update-style interim;

    log-facility local4;

    subnet 10.0.0.0 netmask 255.255.0.0 {
    authoratative;
    range 10.0.10.10 10.0.10.250; ## Guest Network

    # don't let clients update A records for ddns
    ignore client-updates;

    # options
    option subnet-mask 255.255.255.0;
    option broadcast-address 10.0.0.255;

    option domain-name "domain.tld";
    #option domain-name-servers 65.106.1.196,65.106.7.196;
    #option routers 10.0.10.1;
    option domain-name-servers 10.0.0.225;
    option routers 10.0.0.1;

    option ntp-servers 10.0.0.250;

    option netbios-scope "";
    option netbios-node-type 8;

    host ws1 {hardware ethernet 00:13:21:d0:3f:0b;fixed-address 10.0.0.3;}
    host ws2 {hardware ethernet 00:0d:9d:4c:94:4d;fixed-address 10.0.0.5;}
    host ws3 {hardware ethernet 00:0d:9d:4b:35:bd;fixed-address 10.0.0.6;}
    host ws4 {hardware ethernet 00:0b:cd:c3:ee:03;fixed-address 10.0.0.7;}
    }
    ########################################

    The following is what I would have liked to set up. Understandably
    the following won't work because the two networks are not physically
    separated, and there is only one NIC available for dhcp.


    max-lease-time 86400;
    default-lease-time 14400;
    ddns-update-style interim;

    log-facility local4;

    subnet 10.0.10.0 netmask 255.255.255.0 {
    authoratative;
    range 10.0.10.10 10.0.10.250; ## Guest Network

    # don't let clients update A records for ddns
    ignore client-updates;

    # options
    option subnet-mask 255.255.255.0;
    option broadcast-address 10.0.10.255;

    option domain-name "guest.domain.tld";
    option domain-name-servers 65.106.1.196,65.106.7.196;
    option routers 10.0.10.1;
    }


    subnet 10.0.0.0 netmask 255.255.255.0 {
    authoratative;

    # don't let clients update A records for ddns
    ignore client-updates;

    # options
    option subnet-mask 255.255.255.0;
    option broadcast-address 10.0.0.255;

    option domain-name "domain.tld";
    option domain-name-servers 10.0.0.225;
    option routers 10.0.0.1;

    option ntp-servers 10.0.0.250;

    option netbios-scope "";
    option netbios-node-type 8;

    host ws1 {hardware ethernet 00:13:21:d0:3f:0b;fixed-address 10.0.0.3;}
    host ws2 {hardware ethernet 00:0d:9d:4c:94:4d;fixed-address 10.0.0.5;}
    host ws3 {hardware ethernet 00:0d:9d:4b:35:bd;fixed-address 10.0.0.6;}
    host ws4 {hardware ethernet 00:0b:cd:c3:ee:03;fixed-address 10.0.0.7;}
    }
     
    Dan, Jul 31, 2007
    #1
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  2. man dhcpd.conf

    see shared-network

    it's what's you need
     
    Philippe WEILL, Jul 31, 2007
    #2
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  3. Dan

    Dan Guest

    Thank you. I don't know how I missed that in the man page. It was the
    first thing I saw when I opened it. I think I got a little thrown off
    when I saw so many sources (including isc's web page in certain
    places) saying that you need 2 physical interfaces, but I knew it
    could be done somehow.

    For those who would like to see the working config.


    max-lease-time 86400;
    default-lease-time 14400;
    ddns-update-style interim;

    log-facility local4;

    shared-network drlan {

    subnet 10.0.10.0 netmask 255.255.255.0 {
    authoratative;
    range 10.0.10.10 10.0.10.250; ## Guest Network

    # don't let clients update A records for ddns
    ignore client-updates;

    # options
    option subnet-mask 255.255.255.0;
    option broadcast-address 10.0.10.255;

    option domain-name "guest.domain.tld";
    option domain-name-servers 65.106.1.196,65.106.7.196;
    option routers 10.0.10.1;

    host guest-conference-room {hardware ethernet
    00:19:bb:d7:fe:d7;fixed-address 10.0.10.2;}
    }

    subnet 10.0.0.0 netmask 255.255.255.0 {
    authoratative;

    option subnet-mask 255.255.255.0;
    option broadcast-address 10.0.0.255;

    option domain-name "domain.domain.tld";
    option domain-name-servers 10.0.0.225;
    option routers 10.0.0.1;

    option ntp-servers 10.0.0.250;

    host office-ws1 {hardware ethernet 00:0d:9d:4c:
    94:4d;fixed-address 10.0.0.5;}

    }
    }
     
    Dan, Jul 31, 2007
    #3
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