Extraneous Reply to Information Request for Stateless DHCPv6

[Glenn Satchell]

Hi Paul,

that could be the problem, the Server DUID is different in the two responses.

regards,
-glenn

On Mon, March 19, 2018 6:48 am, Paul Fitzgerald wrote:
> I may have identified the culprit. There were additional dhcpd daemons
> running unnoticed.
>
> On Sun, Mar 18, 2018 at 10:00 AM, Paul Fitzgerald <pgf at pgf.org> wrote:
>
>> Hi all,
>>
>> I am working to configure stateless DHCPv6 on my network to provide DNS
>> recursive name servers to Windows clients who have obtained their IPv6
>> addresses using SLAAC.
>>
>> I am running into an issue that is introducing an inconsistency into the
>> process that leads to an undesirable outcome. Basically, I'm seeing an
>> extra Reply message from the DHCP server that doesn't include the DNS
>> recursive name servers. If that Reply message is sent/received first,
>> the
>> client's DNS servers are not set properly.
>>
>> I'm currently using ISC DHCP Server 4.1-ESV-R8.
>>
>> I've tried various permutations, but this is my current dhcpd.conf
>>
>> option dhcp6.name-servers 2001:4860:4860::8888, 2001:4860:4860::8844;
>>
>> shared-network LANv6 {
>>     subnet6 2603:xxxx:xxxx:d0e0::/64 {
>>     }
>> }
>> shared-network WLANv6 {
>>     subnet6 2603:xxxx:xxxx:d0e1::/64 {
>>     }
>> }
>>
>> I am seeing the Information-Request message from the client:
>>
>> DHCPv6
>>     Message type: Information-request (11)
>>     Transaction ID: 0xf4de56
>>     Client Identifier
>>         Option: Client Identifier (1)
>>         Length: 14
>>         Value: 0001000121c9bf4c0056cd39a752
>>         DUID: 0001000121c9bf4c0056cd39a752
>>         DUID Type: link-layer address plus time (1)
>>         Hardware type: Ethernet (1)
>>         DUID Time: Dec 17, 2017 17:50:36.000000000 Central Standard Time
>>         Link-layer address: 00:56:cd:39:a7:52
>>     Option Request
>>         Option: Option Request (6)
>>         Length: 4
>>         Value: 00170018
>>         Requested Option code: DNS recursive name server (23)
>>         Requested Option code: Domain Search List (24)
>>     Elapsed time
>>         Option: Elapsed time (8)
>>         Length: 2
>>         Value: 0000
>>         Elapsed time: 0 ms
>>
>> Then I see *two* Reply messages from the server. If the first message
>> contains the DNS recursive name servers, all is well. Otherwise, the
>> name
>> servers are not configured as expected.
>>
>> DHCPv6
>>     Message type: Reply (7)
>>     Transaction ID: 0xf4de56
>>     Client Identifier
>>         Option: Client Identifier (1)
>>         Length: 14
>>         Value: 0001000121c9bf4c0056cd39a752
>>         DUID: 0001000121c9bf4c0056cd39a752
>>         DUID Type: link-layer address plus time (1)
>>         Hardware type: Ethernet (1)
>>         DUID Time: Dec 17, 2017 17:50:36.000000000 Central Standard Time
>>         Link-layer address: 00:56:cd:39:a7:52
>>     Server Identifier
>>         Option: Server Identifier (2)
>>         Length: 14
>>         Value: 00010001223e067e44d9e79e3682
>>         DUID: 00010001223e067e44d9e79e3682
>>         DUID Type: link-layer address plus time (1)
>>         Hardware type: Ethernet (1)
>>         DUID Time: Mar 15, 2018 23:37:18.000000000 Central Daylight Time
>>         Link-layer address: 44:d9:e7:9e:36:82
>>     DNS recursive name server
>>         Option: DNS recursive name server (23)
>>         Length: 32
>>         Value: 200148604860000000000000000088882001486048600000...
>>          1 DNS server address: 2001:4860:4860::8888
>>          2 DNS server address: 2001:4860:4860::8844
>>
>> DHCPv6
>>     Message type: Reply (7)
>>     Transaction ID: 0xf4de56
>>     Client Identifier
>>         Option: Client Identifier (1)
>>         Length: 14
>>         Value: 0001000121c9bf4c0056cd39a752
>>         DUID: 0001000121c9bf4c0056cd39a752
>>         DUID Type: link-layer address plus time (1)
>>         Hardware type: Ethernet (1)
>>         DUID Time: Dec 17, 2017 17:50:36.000000000 Central Standard Time
>>         Link-layer address: 00:56:cd:39:a7:52
>>     Server Identifier
>>         Option: Server Identifier (2)
>>         Length: 14
>>         Value: 00010001224015df44d9e79e3683
>>         DUID: 00010001224015df44d9e79e3683
>>         DUID Type: link-layer address plus time (1)
>>         Hardware type: Ethernet (1)
>>         DUID Time: Mar 17, 2018 13:07:27.000000000 Central Daylight Time
>>         Link-layer address: 44:d9:e7:9e:36:83
>>
>> Any idea why I'm getting the extra Reply message or how I can eliminate
>> it?
>>
>> Thanks!
>>
>> Paul Fitzgerald
>>
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