Nat hole punch wire protocol

Author: emhane

discv5/discv5-wire.md

@@ -154,6 +154,10 @@ handshake packet.
 
 ![handshake packet layout](./img/handshake-packet-layout.png)
 
+### Notification Packet (`flag = 3`)
+
+Aside from the flag value, this container is identical to a [message packet](#ordinary-message-packet).
+
 ## Protocol Messages
 
 This section lists all defined messages which can be sent and received. The hexadecimal
@@ -291,6 +295,26 @@ TOPICQUERY requests nodes in the [topic queue] of the given topic. The recipient
 request must send one or more NODES messages containing node records registered for the
 topic.
 
+## Protocol Notifications
+
+This section lists all defined notifications which can be sent and received. The hexadecimal
+value in parentheses is the `notification-type`.
+
+### RELAYINIT (0x01)
+
+    message-data      = [inr-enr, tgt-id, nonce]
+    notification-type = 0x01
+    inr-enr           = initiator ENR
+    tgt-id            = 256-bit node ID of target
+    nonce             = uint96    -- nonce of timed out request
+
+### RELAYMSG (0x02)
+
+    message-data      = [init-enr, nonce]
+    notification-type = 0x02
+    init-enr          = initiator ENR
+    nonce             = uint96    -- nonce of timed out request
+
 ## Test Vectors
 
 A collection of test vectors for this specification can be found at