DCCP protocol
============
-Last updated: 10 November 2005
Contents
========
It has a base protocol and pluggable congestion control IDs (CCIDs).
-It is at draft RFC status and the homepage for DCCP as a protocol is at:
- http://www.icir.org/kohler/dcp/
+It is at proposed standard RFC status and the homepage for DCCP as a protocol
+is at:
+ http://www.read.cs.ucla.edu/dccp/
Missing features
================
The DCCP implementation does not currently have all the features that are in
-the draft RFC.
+the RFC.
-In particular the following are missing:
-- CCID2 support
-- feature negotiation
-
-When testing against other implementations it appears that elapsed time
-options are not coded compliant to the specification.
+The known bugs are at:
+ http://linux-net.osdl.org/index.php/TODO#DCCP
Socket options
==============
-DCCP_SOCKOPT_PACKET_SIZE is used for CCID3 to set default packet size for
-calculations.
+DCCP_SOCKOPT_SERVICE sets the service. The specification mandates use of
+service codes (RFC 4340, sec. 8.1.2); if this socket option is not set,
+the socket will fall back to 0 (which means that no meaningful service code
+is present). Connecting sockets set at most one service option; for
+listening sockets, multiple service codes can be specified.
+
+DCCP_SOCKOPT_SEND_CSCOV and DCCP_SOCKOPT_RECV_CSCOV are used for setting the
+partial checksum coverage (RFC 4340, sec. 9.2). The default is that checksums
+always cover the entire packet and that only fully covered application data is
+accepted by the receiver. Hence, when using this feature on the sender, it must
+be enabled at the receiver, too with suitable choice of CsCov.
+
+DCCP_SOCKOPT_SEND_CSCOV sets the sender checksum coverage. Values in the
+ range 0..15 are acceptable. The default setting is 0 (full coverage),
+ values between 1..15 indicate partial coverage.
+DCCP_SOCKOPT_SEND_CSCOV is for the receiver and has a different meaning: it
+ sets a threshold, where again values 0..15 are acceptable. The default
+ of 0 means that all packets with a partial coverage will be discarded.
+ Values in the range 1..15 indicate that packets with minimally such a
+ coverage value are also acceptable. The higher the number, the more
+ restrictive this setting (see [RFC 4340, sec. 9.2.1]).
+
+The following two options apply to CCID 3 exclusively and are getsockopt()-only.
+In either case, a TFRC info struct (defined in <linux/tfrc.h>) is returned.
+DCCP_SOCKOPT_CCID_RX_INFO
+ Returns a `struct tfrc_rx_info' in optval; the buffer for optval and
+ optlen must be set to at least sizeof(struct tfrc_rx_info).
+DCCP_SOCKOPT_CCID_TX_INFO
+ Returns a `struct tfrc_tx_info' in optval; the buffer for optval and
+ optlen must be set to at least sizeof(struct tfrc_tx_info).
+
+
+Sysctl variables
+================
+Several DCCP default parameters can be managed by the following sysctls
+(sysctl net.dccp.default or /proc/sys/net/dccp/default):
+
+request_retries
+ The number of active connection initiation retries (the number of
+ Requests minus one) before timing out. In addition, it also governs
+ the behaviour of the other, passive side: this variable also sets
+ the number of times DCCP repeats sending a Response when the initial
+ handshake does not progress from RESPOND to OPEN (i.e. when no Ack
+ is received after the initial Request). This value should be greater
+ than 0, suggested is less than 10. Analogue of tcp_syn_retries.
+
+retries1
+ How often a DCCP Response is retransmitted until the listening DCCP
+ side considers its connecting peer dead. Analogue of tcp_retries1.
+
+retries2
+ The number of times a general DCCP packet is retransmitted. This has
+ importance for retransmitted acknowledgments and feature negotiation,
+ data packets are never retransmitted. Analogue of tcp_retries2.
+
+send_ndp = 1
+ Whether or not to send NDP count options (sec. 7.7.2).
-DCCP_SOCKOPT_SERVICE sets the service. This is compulsory as per the
-specification. If you don't set it you will get EPROTO.
+send_ackvec = 1
+ Whether or not to send Ack Vector options (sec. 11.5).
+
+ack_ratio = 2
+ The default Ack Ratio (sec. 11.3) to use.
+
+tx_ccid = 2
+ Default CCID for the sender-receiver half-connection.
+
+rx_ccid = 2
+ Default CCID for the receiver-sender half-connection.
+
+seq_window = 100
+ The initial sequence window (sec. 7.5.2).
+
+tx_qlen = 5
+ The size of the transmit buffer in packets. A value of 0 corresponds
+ to an unbounded transmit buffer.
Notes
=====
-SELinux does not yet have support for DCCP. You will need to turn it off or
-else you will get EACCES.
-
-DCCP does not travel through NAT successfully at present. This is because
-the checksum covers the psuedo-header as per TCP and UDP. It should be
-relatively trivial to add Linux NAT support for DCCP.
+DCCP does not travel through NAT successfully at present on many boxes. This is
+because the checksum covers the psuedo-header as per TCP and UDP. Linux NAT
+support for DCCP has been added.
git.samba.org / sfrench / cifs-2.6.git / blobdiff