Changeset 11184 for dotorg/trunk/html

Timestamp:

10/29/09 16:46:10 (5 months ago)

Author:

bittorrent

Message:

updated bep32

Files:

• dotorg/trunk/html/beps/bep_0032.rst (modified) (11 diffs)

dotorg/trunk/html/beps/bep_0032.rst

@@ -1 @@
-BEP: 32
+BEP: XXX
 Title: BitTorrent DHT Extensions for IPv6
 Version: $Revision$
@@ -9 +9 @@
 Content-Type: text/x-rst
 Created: 14-Oct-2009
-Post-History: 15-Oct-2009: Promote same ID in IPv6 and IPv4 nodes. Drop values6. Added some rationales
+Post-History: 
 
 
@@ -17 +17 @@
 This proposal describes a set of extensions to the BitTorrent DHT [#BEP-5]_
 to allow operation over IPv6.
-
-**This is a very early draft**, and **not suitable for implementation**.  Yet.
 
 
@@ -76 +74 @@
 
 
-Double-stack nodes
-------------------
+Dual-stack nodes
+----------------
 
 While conceptually equivalent to a pair of single-protocol nodes,
-a double-stack (IPv4 and IPv6) node can make bootstrap faster and
+a dual-stack (IPv4 and IPv6) node can make bootstrap faster and
 improve the reliability of the protocol by "leaking" data between the
 two DHTs, as described in the following paragraphs.
@@ -88 +86 @@
 '''''''''''''
 
-A double-stack node that is bootstrapping its DHT will send find_nodes
+A dual-stack node that is bootstrapping its DHT will send find_nodes
 requests in order to populate its routing tables.  In order to accelerate
 this process, it should request both "nodes" and "nodes6" fields.
@@ -105 +103 @@
 network outage, however, a node may *ocasionally* send a request for
 "nodes" to an IPv6 node, or a request for "nodes6" to an IPv4 node.
+
+
+Maximum packet size
+-------------------
+
+A node obeying this specification must not send UDP datagrams with
+a payload larger than 1024 octets, and must be able to receive UDP
+datagrams with a payload of 1024 octets or less.  (In the interest of
+robustness, a node should be able to receive datagrams with larger
+payloads.)
+
+  **Rationale**: a UDP datagram with a payload of 1024 octets easily
+  fits within the IPv6 minimum maximum packet size, which is 1280
+  octets [#IPv6]_.  In particular, such a packet will cross a Teredo
+  tunnel with no fragmentation.
+
+  In principle, IPv4 nodes might be unable to reassemble packets
+  larger than 576 octets [#IPv4]_; in practice, however, due to the
+  predominance of Ethernet networks, all IPv4 nodes are able to
+  reassemble packets up to 1500 octets.
+
+
+Source address selection
+------------------------
+
+The IPv6 DHT should use a socket bound to one of the host's global
+unicast IPv6 addresses rather than the "unspecified address" (::/128).
+When selecting to which address to bind, Teredo addresses (addresses
+in 2001:0000::/32) should be avoided if other global unicast addresses
+are available.
+
+  **Rationale**: The DHT relies on the publicly visible IP address of
+  each node to remain constant.  Since multi-homing is common in IPv6,
+  it is particularly important to bind the IPv6 socket to a well-defined
+  address.
+
+  While Teredo traffic can, in principle, be more efficient than
+  native traffic, especially when speaking to other Teredo hosts,
+  experience shows that Teredo routing tends to be brittle; hence,
+  Teredo addresses should be avoided whenever possible.
+
+  The same issues apply to multi-homed IPv4 hosts.  However, in IPv4
+  multi-homing is not as common in IPv6, and in the presence of NAT
+  the issues are somewhat more complicated, so this specification
+  refrains from making any recommendations about binding of IPv4
+  sockets.
+
+
+Changes to the BitTorrent protocol
+==================================
+
+The PORT message, as defined in BEP-5, is extended to work over both
+IPv4 and IPv6.  The information provided by the PORT message only
+applies to the address family it is carried over: a PORT message sent
+over IPv4 only advertises participation in the IPv4 DHT, and a PORT
+message sent over IPv6 only advertises participation in the IPv6 DHT.
+
+  **Rationale**: in the presence of the LTEP extension negotiation
+  protocol [#BEP-10]_, which advertises a peer's addresses across
+  address families, it might be possible to use the PORT message for
+  both address families.  However, since an implementation need not
+  participate in both DHTs, nor use the same port in both DHTs, this
+  specification leaves the role of bridging the two DHTs to the
+  'find_nodes' message (see below).
+
 
 
@@ -154 +217 @@
 The "want" parameter is allowed in the find_nodes and get_peers requests,
 and governs the presence or absence of the "nodes" and "nodes6" parameters
-in the requested reply.  Its value is a string of one or more characters,
-which may include
-
-  * "4": the node requests the presence of a "nodes" key;
-
-  * "6": the node requests the presence of a "nodes6" key.
-
-For future extensibility, other characters may be present in the string,
+in the requested reply.  Its value is a list of one or more strings, which
+may include
+
+  * "n4": the node requests the presence of a "nodes" key;
+
+  * "n6": the node requests the presence of a "nodes6" key.
+
+For future extensibility, other strings may be present in the list,
 and must be silently ignored on reception.
 
-   **Note**: the "want" parameter is currently under discussion.  It
-   has been suggested that it should be renamed to "flags", and that
-   it should be a list of flags rather than a string.  This author
-   is not convinced yet.
+   **Rationale**: the "want" parameter is not intended to carry random
+   sundry flags, which can simply be included in the top-level
+   dictionary of the message.  Extending the "want" parameter without
+   good reason is discouraged.
 
 
@@ -188 +251 @@
 
   **Rationale**: this is an incompatible change to the protocol
-  defined in BEP-5 [#BEP-5]_, which specifies that "nodes" and
-  "values" are mutually exclusive.  However, this change makes the DHT
-  more reliable, and has been deployed by most implementations for
-  over a year with no negative effects.
+  defined in BEP-5, which specifies that "nodes" and "values" are
+  mutually exclusive.  However, this change makes the DHT more
+  reliable, and has been deployed by most implementations for over
+  a year with no negative effects.
 
 When a node receives a get_peers request and it has contact
@@ -207 +270 @@
   **Rationale**: if the requesting node is a single-stack node, it has
   no interest in values of the other address family.  If the
-  requesting node is a double-stack node, then it must perform the two
+  requesting node is a dual-stack node, then it must perform the two
   announces in parallel; providing both sets of data in both sets of
   replies merely increases the amount of traffic without giving any
@@ -235 +298 @@
    (http://www.bittorrent.org/beps/bep_0005.html)
 
+.. [#BEP-10] BEP_0010.  Extension Protocol.
+   (http://www.bittorrent.org/beps/bep_0010.html)
+
+.. [#IPv6] RFC 2460.  Internet Protocol, Version 6 (IPv6) Specification.
+   S. Deering, R. Hinden. December 1998.
+
+.. [#IPv4] RFC 791.  Internet Protocol.  J. Postel.  September 1981.
 
 
@@ -240 +310 @@
 =========
 
-This document has been placed in the public domain.
+This document is in the public domain.