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[lwip-devel] [patch #9737] Fix DHCPv6 DNS server assignment

From: David J. Fiddes
Subject: [lwip-devel] [patch #9737] Fix DHCPv6 DNS server assignment
Date: Thu, 27 Dec 2018 07:16:31 -0500 (EST)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0


                 Summary: Fix DHCPv6 DNS server assignment
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: davefiddes
            Submitted on: Thu 27 Dec 2018 12:16:28 PM UTC
                Category: IPv6
                Priority: 5 - Normal
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None



This patch fixes a problem with the storage of DNS server addresses received
via DHCPv6. The IP address type is not set which causes the address to be
truncated to the first 32-bits of the 128-bit IPv6 address.

The fix is to set the address type of the DNS server to IPv6 when it is being

I have tested this as part of the ESP8266 Arduino project on a WeMos D1 R1 on
a network where the router provides both ND6 RDNSS and DHCPv6 DNS support. The
stack was configured to use either option and  a simple IPv6 DNS sample from
the ESP8266 Arduino project used to verify that the correct DNS server is

There is a race condition with IPv4 DHCP which can cause the DNS server
address to be overwritten occasionally. Disabling IPv4 DHCP support stops this

It is not straightforward to test DHCPv6 NTP support on my network but code
inspection reveals that this bug is not present there.


File Attachments:

Date: Thu 27 Dec 2018 12:16:28 PM UTC  Name: dhcpv6-dns-fix.diff  Size: 625B  
By: davefiddes



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