Cherry-pick PPP DNS fixes from PR 3181 #3064
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rlubos
approved these changes
Jul 21, 2025
When Kconfig option CONFIG_NET_L2_PPP_OPTION_DNS_USE is enabled, Zephyr should request two DNS addresses in IPCP negotiation by sending IPCP ConfReq for DNS otions using 0.0.0.0 as an address. Remote peer may offer DNS by sending IPCP ConfNak with proper address. This is explained in RFC 1332 and RFC 1877 (DNS extension). When no DNS is required, we should only send IPCP ConfReq for IP address, without having DNS fields in the same request. However, when PPP is configured to serve a DNS using Kconfig option CONFIG_NET_L2_PPP_OPTION_SERVE_DNS it should serve the DNS address in the IPCP ConfNak message and from the ipcp.peer_options structure, not from the ipcp.my_options. This might break backward compatibility outside this repository as DNS addresses used to be served from ipcp.my_options. Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no> (cherry picked from commit 5a31f3d)
There are cases, for example when peer is requesting two DNS addresses, but we can only give one, we should reject the secondary DNS request first, before sending NAK to acceptable options. Option parser can reject a parameter by returning -ENOTSUP and when it wants to NAK the parameter, it returns -EINVAL. On RFC 1661: Configure-Reject If some Configuration Options received in a Configure-Request are not recognizable or are not acceptable for negotiation (as configured by a network administrator), then the implementation MUST transmit a Configure-Reject. Configure-Nak If every instance of the received Configuration Options is recognizable, but some values are not acceptable, then the implementation MUST transmit a Configure-Nak. So as stated by RFC, we should start the negotiation by rejecting all parameters that we cannot configure. I added an example of rejecting DNS requests, if we don't have those. Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no> (cherry picked from commit d5f4ca3)
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Cherry-pick PPP DNS fixes from PR zephyrproject-rtos/zephyr#93181