Check https://datatracker.ietf.org/doc/html/draft-thatcher-ice-network-cost

Context

libwebrtc sends STUN attributes with type 0xC057 which is defined here: https://datatracker.ietf.org/doc/html/draft-thatcher-ice-network-cost

Rationale: https://mailarchive.ietf.org/arch/msg/ice/gOAus-n6Ll3hfTfBC6zVd6_VTkE/

We're using 0xC057 for an experimental "network cost" attribute, which is described in this draft: https://tools.ietf.org/html/draft-thatcher-ice-network-cost-00

This is used in order to communicate an endpoint's preference for different networks (if the endpoint is using multiple network interfaces), so that the controlling ICE endpoint can select the preferred one based on certain criteria. We can't just use the ICE candidate priority, because the "type preference" part of the priority (local, stun, relay) takes precedence over the "local preference". There are other reasons as well, which are discussed in the draft.

Notes

• The draft expired in 2016.