diff --git a/meshtastic/mesh.proto b/meshtastic/mesh.proto
index fb585b9..219a7fc 100644
--- a/meshtastic/mesh.proto
+++ b/meshtastic/mesh.proto
@@ -988,6 +988,10 @@ message RouteDiscovery {
 
   /*
    * The list of SNRs (in dB, scaled by 4) in the route towards the destination.
+   * Special values (ouside normal SNR range) are used as flags:
+   * -128 : Unknonw SNR
+   * -127 : MQTT hop
+   *  127 : UDP hop
    */
   repeated int32 snr_towards = 2;
 
@@ -998,6 +1002,10 @@ message RouteDiscovery {
 
   /*
    * The list of SNRs (in dB, scaled by 4) in the route back from the destination.
+   * Special values (ouside normal SNR range) are used as flags:
+   * -128 : Unknonw SNR
+   * -127 : MQTT hop
+   *  127 : UDP hop
    */
   repeated int32 snr_back = 4;
 }