DHCP Client handles RFC 3442 incorrectly

Question

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.

Answer 1

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,

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Answer 2

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

Answer 3

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).