[Bug 199378] [patch] dhclient violates RFC2131 when sending early DHCPREQUEST message to re-obtain old IP

[bugzilla-noreply]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199378

David Bright  changed:

   What|Removed |Added

 Status|New |In Progress
 CC||d...@freebsd.org
   Assignee|freebsd-bugs@FreeBSD.org|d...@freebsd.org

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[Bug 199378] [patch] dhclient violates RFC2131 when sending early DHCPREQUEST message to re-obtain old IP

[bugzilla-noreply]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199378

Bug ID: 199378
   Summary: [patch] dhclient violates RFC2131 when sending early
DHCPREQUEST message to re-obtain old IP
   Product: Base System
   Version: 11.0-CURRENT
  Hardware: Any
OS: Any
Status: New
  Keywords: patch
  Severity: Affects Many People
  Priority: ---
 Component: bin
  Assignee: freebsd-bugs@FreeBSD.org
  Reporter: f...@opal.com
  Keywords: patch

Created attachment 155476
  -- https://bugs.freebsd.org/bugzilla/attachment.cgi?id=155476action=edit
patch to cause early DHCPREQUEST broadcasts to be sent using source IP 0.0.0.0

When dhclient first starts, if an old IP address exists in the dhclient.leases
file, dhclient(8) sends early DHCPREQUEST message(s) in an attempt to re-obtain
the old IP address again.  These messages contain the old IP as a
requested-IP-address option in the message body (correct) but the message also
uses the old IP address as the packet's source IP (incorrect).

RFC2131 sec 4.1 states:

   DHCP messages broadcast by a client prior to that client obtaining
   its IP address must have the source address field in the IP header
   set to 0.

The use of the old IP as the packet's source address is incorrect if (a) the
computer is now on a different network or (b) it is on the same network, but
the old IP has been reallocated to another host.

The attached patch fixes things to use 0.0.0.0 as the source IP without
removing any existing functionality.  Any previously-used old IP is still
requested in the body of an early DHCPREQUEST message.

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