Re: Ip Helper doesn't work?

Discussion in 'Cisco' started by Make, Oct 19, 2005.

  1. Make

    Make Guest

    "Make" <> kirjoitti viestissä:...
    > Try this:
    > no service dhcp
    > interface FastEthernet0/1
    > no ip directed-broadcast
    > interface FastEthernet0/2
    > no ip directed-broadcast
    >
    >> I use a 3550 L2/L3 switch and I need to use a remote dhcp server.
    >>
    >> I configured it on my router but it didn't work.

    >
    >
     
    Make, Oct 19, 2005
    #1
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  2. Make

    Merv Guest

    Merv, Oct 19, 2005
    #2
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  3. Make

    root Guest

    Merv wrote:
    > What Martin says about the server sending to destination port 68 is
    > correct.
    >
    > see the Cisco document on troubleshooting DHCP. It has sniffer traces
    > that clearly shows what happens to the DHCP packet port numbers - the
    > relay agent changes the source port number from 68 to 67 and expects it
    > to come back to destination port 67.
    >
    > http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml
    >



    Thank you very much. I hadn't notice the mistake of the dhcp server that
    insist to answer to a wrong destination port.

    Probably it can be a common mistake because I tried with two kind of
    server one under linux and one under wnt.

    Now I'll look for a workaround.
     
    root, Oct 20, 2005
    #3
  4. Make

    Merv Guest

    Check thast the DHCP server you plan to use is compliant with RFC 2131,

    4.1 Constructing and sending DHCP messages, paragraph 5

    " If the 'giaddr' field in a DHCP message from a client is non-zero,
    the server sends any return messages to the 'DHCP server' port on
    the
    BOOTP relay agent whose address appears in 'giaddr'. "

    The giaddr field will be non-zero in your case.
     
    Merv, Oct 20, 2005
    #4
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