DHCP bug found

Discussion in 'Tomato Firmware' started by Pro29, Feb 8, 2008.

  1. Pro29

    Pro29 LI Guru Member

    DHCP on my LinkSys WRT54GL not receive IP-adress. My provider dropped all DHCP-reguest, if param "secs" in DHCP header <=2. Any firmware send param "secs"=0 by default. Windows XP send "secs"=0, 768, 2816, 6912.
    How to modify firmware?
  2. mstombs

    mstombs Network Guru Member

    Tomato uses a version of busybox dhcpc, how do you get that information about what "secs" is set to? Wireshark on the dhcp discover process?
  3. Pro29

    Pro29 LI Guru Member

    I'm use "SoftPerfect Network Protocol Analyser". I'm saved DHCP-packets Windows XP and router, has compared them.
    Then I began to send packages, emulating work of a router. It is by practical consideration established, that at secs <=2 answers from DHCP do not come.

    P.S. Forgive for my English :)
  4. HennieM

    HennieM Network Guru Member

    See http://www.faqs.org/rfcs/rfc2131.html

    As I understand it: The "secs" parameter is a dynamic value filled in by the client, indicating how long ago it started the DHCP acquisition. The server should not use this field (and thus not be concerned with the actual "secs" value), except for verifying that the DHCPREQUEST now received by the server, is from the same client that sent the previous DHCPDISCOVER, by checking that the "secs" in the 2 messages are the same.

    You can perhaps check on your sniffer if the same "secs" value is used by Tomato during DHCPDISCOVER and DHCPREQUEST. If not, the problem is most likely with the udhcpc in busybox.

    If the DHCPDISCOVER and DHCPREQUEST "secs" are the same, I would deduce that your ISP's DHCP server(s) are buggy.
  5. Pro29

    Pro29 LI Guru Member

    The problem with DHCP is precisely established by several different people in several cities. It is shown only at one provider. For routers ASUS already there is an firmware in which parameter secs=3, and all works. The provider refuses to help and does not see a problem. Me interests how to change value secs.
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