From: Nikos Mavrogiannopoulos <nmav@gnutls.org>
Date: Thu, 1 Sep 2011 08:02:19 +0000 (+0200)
Subject: more doc on MTU.
X-Git-Tag: gnutls_3_0_2~3
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d70186fe142d0943272a10b57d71e359aeb707e7;p=thirdparty%2Fgnutls.git

more doc on MTU.
---

diff --git a/doc/cha-bib.texi b/doc/cha-bib.texi
index a27509b2c5..b9791df246 100644
--- a/doc/cha-bib.texi
+++ b/doc/cha-bib.texi
@@ -172,4 +172,8 @@ Work in progress, available from @url{http://tools.ietf.org/html/draft-pechanec-
 R. J. Anderson, "Security Engineering: A Guide to Building Dependable Distributed Systems", 
 John Wiley \& Sons, Inc., 2001.
 
+@item @anchor{RFC4821}[RFC4821]
+M. Mathis, J. Heffner, "Packetization Layer Path MTU Discovery", March 2007,
+available from @url{http://www.ietf.org/rfc/rfc4821.txt}.
+
 @end table
diff --git a/doc/cha-gtls-app.texi b/doc/cha-gtls-app.texi
index cd6ad2f18c..bf65319483 100644
--- a/doc/cha-gtls-app.texi
+++ b/doc/cha-gtls-app.texi
@@ -250,17 +250,17 @@ same way as a system call would. The only exception is @funcref{gnutls_record_se
 which if interrupted subsequent calls need not to include the data to be
 sent (can be called with NULL argument).
 
-The @code{select()} system call can also be used in combination with the
-@acronym{GnuTLS} functions. @code{select()} allows monitoring of sockets
+The @funcintref{select} system call can also be used in combination with the
+@acronym{GnuTLS} functions. @funcintref{select} allows monitoring of sockets
 and notifies on them being ready for reading or writing data. Note however
 that this system call cannot notify on data present in @acronym{GnuTLS}
 read buffers, it is only applicable to the kernel sockets API. Thus if
 you are using it for reading from a @acronym{GnuTLS} session, make sure
 the session is read completely. That can be achieved by checking there 
 are no data waiting to be read (using @funcref{gnutls_record_check_pending}), 
-either before the @code{select()} system call, or after a call to
+either before the @funcintref{select} system call, or after a call to
 @funcref{gnutls_record_recv}. @acronym{GnuTLS} does not keep a write buffer,
-thus when writing @code{select()} need only to be consulted.
+thus when writing @funcintref{select} need only to be consulted.
 
 In the DTLS, however, @acronym{GnuTLS} might block due to timers
 required by the protocol. To prevent those timers from blocking a DTLS handshake,
@@ -288,14 +288,22 @@ and proceed to a proper handshake.
 @showfuncdesc{gnutls_dtls_prestate_set}
 
 
-Note that the above apply to server side only. The client side cookie handling
-is part of @funcref{gnutls_handshake}. However both client and server
-side should set the correct maximum transfer unit for
+Note that the above apply to server side only and they are not mandatory to be
+used. Not using them, however, allows denial of service attacks.
+The client side cookie handling is part of @funcref{gnutls_handshake}. 
+
+Datagrams are typically restricted by a maximum transfer unit (MTU). For that
+both client and server side should set the correct maximum transfer unit for
 the layer underneath @acronym{GnuTLS}. This would allow proper fragmentation
-of DTLS messages.
+of DTLS messages and prevent messages from being silently discarded by the
+transport layer. The ``correct'' maximum transfer unit can be obtained through
+a path MTU discovery mechanism @xcite{RFC4821}.
 
 @showfuncdesc{gnutls_dtls_set_mtu}
 
+@showfuncdesc{gnutls_dtls_get_mtu}
+@showfuncdesc{gnutls_dtls_get_data_mtu}
+
 @node Priority Strings
 @section Priority strings
 
diff --git a/doc/latex/gnutls.bib b/doc/latex/gnutls.bib
index 7d07e8904d..d5ccfdfb42 100644
--- a/doc/latex/gnutls.bib
+++ b/doc/latex/gnutls.bib
@@ -236,8 +236,17 @@
 	title = "{Using OpenPGP Keys for Transport Layer Security (TLS) Authentication}",
 	month = "February",
 	year = "2011",
-	note = "Available from \url{http://tools.ietf.org/html/rfc6091}",
-	url = "http://tools.ietf.org/html/rfc6091"
+	note = "Available from \url{http://www.ietf.org/rfc/rfc6091.txt}",
+	url = "http://www.ietf.org/rfc/rfc6091.txt"
+}
+
+@Misc{ RFC4821,
+	author = "Matt Mathis and John Heffner",
+	title = "{Packetization Layer Path MTU Discovery}",
+	month = "March",
+	year = "2007",
+	note = "Available from \url{http://www.ietf.org/rfc/rfc4821.txt}",
+	url = "http://www.ietf.org/rfc/rfc4821.txt"
 }
 
 @Misc{ TLSCOMP,