From 36e39d72c7b5cec23aa987193aa525e2286d9423 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Wed, 3 Aug 2011 09:44:38 +0100
Subject: [PATCH] WIP DNS notes

---
 NOTES.ip-over-dns | 70 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/NOTES.ip-over-dns b/NOTES.ip-over-dns
index c706b55..ea4c0f4 100644
--- a/NOTES.ip-over-dns
+++ b/NOTES.ip-over-dns
@@ -10,3 +10,73 @@ Encoding:
   - client splits packet into appropriate fragments
   - makes A queries for
      
+
+
+
+We use CNAME queries.  The request/response Q and R are bit-encoded
+into the labels of the query domain and answer section domains,
+respectively.
+
+The server maintains a local cache of questions we have been asked and
+answers we gave.  Neither side ever retries packets; so any responses
+from our server's cache are due to resolvers between the client and
+the server.
+
+
+Requests by client:
+
+ Create Association
+	Q	client-init-nonce
+		4 bits		Length of client-message-nonce in bits,
+				 0 meaning 16; default is 8
+		remaining	Unfragmented response message data bytes
+
+	R	5 bits		Length of associd in bits
+				 0 meaning 32; default is 8
+		associd
+		queue-len-info
+		remaining=payload
+
+ Request Down
+	Q	associd
+		client-message-nonce
+
+	R	queue-len-info
+		remaining=payload
+
+ Submit Up
+	Q	associd
+		client-message-nonce
+		payload
+
+	R	queue-len-info
+		remaining	Unfragmented response message data bytes
+
+queue-len-info :=
+		4 bits		Double-logarithmic server queue length
+	# ciel(log_2( Number of bytes of queued message data ))
+	#  except that if no queued message data, value is 0
+
+payload :=
+	[ If there is actually any data to send:
+		1 bit		Only fragment ?
+	  [ If not only fragment:
+		1 bit		Final fragment ?
+		12 bits		Fragment offset
+	    [ In packets from server:
+		8 bits		netlink-packet-sequence-number
+		# In payloads from client, the client-message-nonce
+		#  is used for reassembly.
+	    ]
+	  ]
+		remaining	Data Bytes
+	]
+
+associd :=	n bits		as specified in Create Association response
+
+client-init-nonce :=	64 bits		Random number
+client-message-nonce := some bits	Sequence number, starts at random value
+	# Ie if we start having more than 255 queries outstanding, we're
+	# going to start losing things.  With our default TTL of 1s and
+	# a compliant DNS server, that might limit us to 255 packets/sec.
+	# With noncompliant DNS servers it might reduce available bandwidth.
-- 
2.30.2