DHCP relay agent versus Option 3; Routers Option

Discussion in 'Cisco' started by lcorrigan, Sep 25, 2006.

  1. lcorrigan

    lcorrigan Guest

    Could someone explain to me the difference between using a router as a
    DHCP relay agent (option 82) and configuring option 3 (routers option)
    on the DHCP server?
    I currently need to set up a server to use option 3 to reproduce an
    issue in a test environment but I need a good "real-life" scenario to
    assist. Would it be something like this for option 3?

    DHCPclient >>>>>>> Remote router >>>>>>> DHCP Server
    Where the "DHCP Server" would send the "Remote Router" client-side IP
    address in the option 3 section of the DHCP Offer ? Or does the the
    remote router need to be set as a relay-agent to have this make sense?

    Would it ever make sense to have:

    DHCPclient>>>>>>>DHCP Server, where Option 3 is still necessary in the
    DHCP Offer? ie: Option 3 contains the DHCP Server's client side

    I already know how to set up option 3 and relay agents / helper ip
    address but just need more on the theory of the option 3 and the
    scenarios where it would be used.
    Any help on this would be appreciated.
    lcorrigan, Sep 25, 2006
    1. Advertisements

  2. Hi

    here is real-life scenario:


    router1 has ip-helper dhcp-server-ip

    make sure ALL routers from host to server DON'T have "no service dhcp"
    (usually it's enabled by default)

    on the server (here is part of the config file for isc-dhcpd):
    subnet netmask {
    option routers;

    hope that helped
    Roman Nakhmanson
    Roman Nakhmanson, Sep 25, 2006
    1. Advertisements

  3. lcorrigan

    lcorrigan Guest

    lcorrigan, Sep 27, 2006
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.