DHCP Client handles RFC 3442 incorrectly

Tom Siewert 6 Reputation points
2021-11-29T17:25:49.797+00:00

While debugging an issue with the routing I have discovered that the DHCPv4 client in the Windows Networking stack does not handle RFC 3442 correctly. When a DHCPv4 server is sending both, the routers and the classless-routes option (and the classless-routes does not include a default route), the DHCP client installs a default route. According to the RFC, the client MUST ignore router option and only install the routes from the classless-routes option (See section DHCP Client Behavior), even if the DHCP server is misbehaving in this case.

Windows DHCP
Windows DHCP
Windows: A family of Microsoft operating systems that run across personal computers, tablets, laptops, phones, internet of things devices, self-contained mixed reality headsets, large collaboration screens, and other devices.DHCP: Dynamic Host Configuration Protocol (DHCP). A communications protocol that lets network administrators manage centrally and automate the assignment of Internet Protocol (IP) addresses in an organization's network.
926 questions
Windows Server
Windows Server
A family of Microsoft server operating systems that support enterprise-level management, data storage, applications, and communications.
8,277 questions

3 answers

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  1. Limitless Technology 37,356 Reputation points
    2021-11-30T19:48:04.96+00:00

    Hello @Tom Siewert

    This issue has been discussed in the next post, which adds some layers to the complexity of persistent routes handling over Microsoft DHCP clients.

    https://social.technet.microsoft.com/Forums/en-US/153965e6-5d47-4d2e-bfaf-d859b7bce3ea/problem-with-persistent-routes-and-option-249-classless-static-routes-in-dhcp?forum=w7itpronetworking

    Hope this helps with your query,

    -----------

    --If the reply is helpful, please Upvote and Accept as answer--

  2. Tom Siewert 6 Reputation points
    2021-12-13T19:33:38.887+00:00

    Hi @Limitless Technology ,

    thanks for your link. I'm afraid to tell you that your mentioned thread is not the same issue about. The issue I described says that the DHCP Client is installing wrong routes which should not get installed. However, the author of your thread is talking about routes which are not persistent.

    Cheers,
    Tom

  3. Tom Siewert 6 Reputation points
    2022-02-02T22:03:34.71+00:00

    bump

    The issue is still present and no solution so far other than modifying the DHCP server to not include the routers option (which is not quite easy for internal reasons).