A local-only border crossing (a regional or bilateral checkpoint restricted to local residents or citizens of the adjacent countries) is typically (always?) only open to the two specific nationalities of the two adjacent countries. Example: Dak Dam Border Police Station (Cambodia) / Buprang Border Gate Customs Branch (Vietnam). Third-country nationals are barred from using them and are required to use an official international port of entry.
However, I am curious if there are any legal or geographical exceptions to this, e.g. in tri-border areas (tripoints) where three countries meet (and possibly quadripoints or higher-order multipoints). Are there any local land border crossing that operates under a trilateral (or multilateral) agreement, i.e. that allows citizens of three (or more) specific neighboring countries to cross, while remaining strictly closed to general international travelers or other nationalities? That'll help me understand whether classifying borders as international vs. only open to 2 local nationalities is correct.