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
    address?

    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
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  2. Hi

    here is real-life scenario:

    host-----10.1.1.0/24--router1---router2----router3---router4-------10.1.12.0/24----DHCP-server

    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 10.1.1.0 netmask 255.255.255.0 {
    range 10.1.1.101 10.1.1.200;
    option routers 10.1.1.1;
    }

    hope that helped
    Roman Nakhmanson




    Icorrigan wrote:
    > 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
    > address?
    >
    > 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.
    Roman Nakhmanson, Sep 25, 2006
    #2
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  3. lcorrigan

    lcorrigan Guest

    Roman Nakhmanson wrote:
    > Hi
    >
    > here is real-life scenario:
    >
    > host-----10.1.1.0/24--router1---router2----router3---router4-------10.1.12.0/24----DHCP-server
    >
    > 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 10.1.1.0 netmask 255.255.255.0 {
    > range 10.1.1.101 10.1.1.200;
    > option routers 10.1.1.1;
    > }
    >
    > hope that helped
    > Roman Nakhmanson
    >
    >
    >
    >
    > Icorrigan wrote:
    > > 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
    > > address?
    > >
    > > 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 27, 2006
    #3
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