This draft https://datatracker.ietf.org/doc/draft-li-apn-framework/ specifies that the APN marking will be encapsulated in the outer tunnel encapsulation and removed together with the tunnel encapsulation at the end of each tunnel. In the same draft, we have also listed the APN Attribute Conveying Requirements https://datatracker.ietf.org/doc/html/draft-li-apn-framework-04#section-5.1, the [REQ 1d] is that “APN ID MUST be acquired from the existing available information of the packet header without interference into the payload.” APN works within a limited domain and the APN ID will be only meaningful to this network domain. The interpretation of the values of these fields is a local matter within the APN domain.