[lwip-devel] [bug #51623] DHCP request XID should probably be regenerated for INIT-REBOOT

[Ambroz Bizjak]

URL:
  <http://savannah.nongnu.org/bugs/?51623>

                 Summary: DHCP request XID should probably be regenerated for
INIT-REBOOT
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: abizjak
            Submitted on: Sun 30 Jul 2017 03:27:36 PM UTC
                Category: DHCP
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head

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Details:

In bug #40303 the DHCP client was changed to never regenerate an XID when
sending a DHCPREQUEST. This was because RFC 2131 requires that the DHCPREQUEST
following a DHCPOFFER uses the same XID as the offer (and therefore the same
as DHCPDISCOVER).

However it is required to generate a new XID when entering the INIT-REBOOT
state (4.4.2 Initialization with known network address). Currently lwIP does
not do that.

I have checked the behavior of Windows 10 and dhclient (Ubuntu 16.10) and both
generate a new XID in this case (after link goes back up).

I also checked the XID generation of these systems for RENEWING and REBINDING,
and Windows generates new XIDs while dhclient does not, so I suppose lwIP is
fine in this respect if it keeps using the same XID as it is now, I only
recommend to change to generating a new XID when the REBOOTING state is
entered (in dhcp_network_changed).




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