Preparation for dispatcher-less endpoints. Reduce the range of IDs used for SCMP requests, to be forward-compatible with the default range for port-dispatching in the router.
In the dispatcher-less future, the router will forward SCMP reply messages to an application's underlay port determined based on the SCMP message ID. For this, the router will have a configurable range of ports for which it applies the dispatching, allowing dispatcher-ful and dispatcher-less endpoints to coexist. This port range will need to be disjoint from the port range currently used by the dispatcher and SCMP request identifiers.
matzf
commented
3 months ago 
Preparation for dispatcher-less endpoints. Reduce the range of IDs used for SCMP requests, to be forward-compatible with the default range for port-dispatching in the router.
In the dispatcher-less future, the router will forward SCMP reply messages to an application's underlay port determined based on the SCMP message ID. For this, the router will have a configurable range of ports for which it applies the dispatching, allowing dispatcher-ful and dispatcher-less endpoints to coexist. This port range will need to be disjoint from the port range currently used by the dispatcher and SCMP request identifiers.
For more details, see design document, #4280.