[Bug 629] New: Non-compliant DHCP servers and udhcpc

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=629

           Summary: Non-compliant DHCP servers and udhcpc
           Product: Busybox
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Networking
        AssignedTo: unassigned at busybox.net
        ReportedBy: nhathaway at ubiquisys.com
                CC: busybox-cvs at busybox.net
   Estimated Hours: 0.0


The problem occurs with DHCP servers that are not compliant with RFC2131. When
Busybox sends a renewal request, it sends the request directly to the server it
last had an assignment from, i.e. unicast not broadcast. The DHCP server should
reply with a unicast response, i.e. directly addressed to the requesting
Busybox, not broadcast. Unfortunately some DHCP servers are non compliant in
this respect and send the reply back as a broadcast messages - Busybox is not
set up to receive this message in this state and so they are discarded.

If Busybox does not get a response to the unicast requests from the DHCP server
it switches back to the broadcast of the request that it first used on startup,
in this state it is able to receive broadcast responses from the DHCP server
and the IP address is re-allocated.

The net effect of this is that, with non-compliant servers, Busybox loses its
IP address, the link drops out, and then within a few seconds it is back up
again. This disrupts traffic on the system and can cause certain services to
drop out (exit and/or restart).

>From our testing some examples of compliant behaviour are Dell (Linux) servers
configured as DHCP servers, and Linksys routers are compliant. However some
examples of non-compliant behaviour are Netopia (Motorola) routers and Draytek
routers.

Should Busybox be modified to cope with non-compliant servers, or should
another work-around be sought?


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