viktor-iarmola:

When odhcp6c runs in unknown mode (-N try as default and -P x without -F) it tries to determine its actual mode from received advertisements.

Normally, when there are both stateful (with IA_NA or IA_PD) and stateless (without both IA_NA and IA_PD) advertisements in the network - it works fine because odhcp6c prefers stateful ones and prioritizes them higher. However, some setups in the wild interfere with this scenario via either of:

• stateful and stateless advertisements come with the same server DUID - in that case if stateless advertisement comes last we will go into stateless mode despite there being stateful advertisements available;
• stateful advertisements are "late" and odhcp6c only receives stateless ones during its first solicit session.

Both of these cases could seemingly be avoided by -N force and/or -F options, which will force odhcp6c to run in "stateful" mode and ignore advertisements not carrying specific option. However, it is currently impossible to express the intention of wishing to accept only advertisements carrying //either// IA_NA or IA_PD or both of them - and ignoring advertisement without both IA_NA and IA_PD.

To solve this a pull request was created to support a new option for odhcp6c - -D to discard stateless advertisements.
Please take a look at the github PR with some extra details: openwrt/odhcp6c#69