Extraneous Reply to Information Request for Stateless DHCPv6

[Paul Fitzgerald]

 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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