How to block bootp/dhcp broadcasting on cisco routers?

Discussion in 'Cisco' started by Faustino Dina, Sep 28, 2004.

  1. Hi,

    How can I block bootp/dhcp broadcast at cisco routers?

    Thanks in advance

    --
    Faustino Dina
    --------------------------------------------------------
    If my email address starts with two 'f'
    drop the first 'f' when mailing me.
     
    Faustino Dina, Sep 28, 2004
    #1
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  2. Faustino Dina

    Ivan Ostreš Guest

    In article <>, says...
    > Hi,
    >
    > How can I block bootp/dhcp broadcast at cisco routers?
    >


    Router is by definition a border of broadcast domain so you don't
    actually need to do anything (if you don't have 'ip helper-address' or
    'directed broadcast' commands in your config).



    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Sep 28, 2004
    #2
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  3. > Router is by definition a border of broadcast domain so you don't
    > actually need to do anything (if you don't have 'ip helper-address' or
    > 'directed broadcast' commands in your config).


    Well, that exactly was my assumption. I configured dhcp servers on two
    segments of my wan 10.10.10.0/24 and 10.10.34.0/24. But when I connect a
    test PC to the 10.10.10.0/24 subnet, it receives the address leased by the
    dhcp server at 10.10.34.0/24 'cause it answers first. ANd the address it
    leases is a 10.10.34.x one. Then how 10.10.34.0/24 knows of the dhcp request
    broadcast. I checked my routers and none of then is configured with 'ip
    helper-address' nor 'directed broadcast' commands Even I tryed "no ip
    forward-protocol udp bootpc" and "no ip forward-protocol udp bootps" but in
    both cases the routers answered there was no port to delete...

    What to do?
    Thanks for your replay

    Faustino
     
    Faustino Dina, Sep 28, 2004
    #3
  4. Faustino Dina

    RC Guest

    No need to post you problem twice. But a full config would help. And maybe a
    description of the physical layout (any chance you have a loop?).

    "Faustino Dina" <> wrote in message
    news:...
    > > Router is by definition a border of broadcast domain so you don't
    > > actually need to do anything (if you don't have 'ip helper-address' or
    > > 'directed broadcast' commands in your config).

    >
    > Well, that exactly was my assumption. I configured dhcp servers on two
    > segments of my wan 10.10.10.0/24 and 10.10.34.0/24. But when I connect a
    > test PC to the 10.10.10.0/24 subnet, it receives the address leased by the
    > dhcp server at 10.10.34.0/24 'cause it answers first. ANd the address it
    > leases is a 10.10.34.x one. Then how 10.10.34.0/24 knows of the dhcp

    request
    > broadcast. I checked my routers and none of then is configured with 'ip
    > helper-address' nor 'directed broadcast' commands Even I tryed "no ip
    > forward-protocol udp bootpc" and "no ip forward-protocol udp bootps" but

    in
    > both cases the routers answered there was no port to delete...
    >
    > What to do?
    > Thanks for your replay
    >
    > Faustino
    >
    >
     
    RC, Sep 28, 2004
    #4
  5. > No need to post you problem twice. But a full config would help. And maybe
    a
    > description of the physical layout (any chance you have a loop?).


    Thanks, I found what is the problem. These weird subnetworks are connected
    to the 10.10.10.0/24 via a wireless shortwave system. The provider
    configured this system such a way that the remote pcs can be configured with
    10.10.10.x addresses. I think it is similar to have one interface with a
    secondary address so there are two logical subnets in the same physical
    link. That is why dhcp broadcast from 10.10.10.0 reached the dhcp server at
    10.10.34.0/24. I should investigate it later.
    Thanks for your attention

    Faustino
     
    Faustino Dina, Sep 29, 2004
    #5
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