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[PATCH 2.10-357-ga0902db 1/1] Add CSn definitions to netinet/ip.h

The fix in bugid 10789 could be interpreted to mean that DSCP markings (IPTOS_DSCP_AF21 .. IPTOS_DSCP_EF)
are used exclusively for marking in the Internet today.

That would be an incorrect reading.

The old IPTOS_PREC_xxx values are still in use, but have been renamed as CS0 ... CS7.

This patch clarifies that.

Quoting the additional RFC 2474:

2.  Terminology Used in This Document

   Behavior Aggregate: a collection of packets with the same codepoint
   crossing a link in a particular direction.  The terms "aggregate" and
   "behavior aggregate" are used interchangeably in this document.

   Classifier: an entity which selects packets based on the content of
   packet headers according to defined rules.

   Class Selector Codepoint: any of the eight codepoints in the range '
   xxx000' (where 'x' may equal '0' or '1').  Class Selector Codepoints
   are discussed in Sec. 4.2.2.

   Class Selector Compliant PHB: a per-hop behavior satisfying the Class
   Selector PHB Requirements specified in Sec.

   Codepoint: a specific value of the DSCP portion of the DS field.
   Recommended codepoints SHOULD map to specific, standardized PHBs.
   Multiple codepoints MAY map to the same PHB.


4.2.2  Subsuming IP Precedence into Class Selector Codepoints

   A specification of the packet forwarding treatments selected by the
   IP Precedence field today would have to be quite general; probably
   not specific enough to build predictable services from in the
   differentiated services framework.  To preserve partial backwards
   compatibility with known current uses of the IP Precedence field
   without sacrificing future flexibility, we have taken the approach of
   describing minimum requirements on a set of PHBs that are compatible
   with most of the deployed forwarding treatments selected by the IP
   Precedence field.  In addition, we give a set of codepoints that MUST
   map to PHBs meeting these minimum requirements.  The PHBs mapped to
   by these codepoints MAY have a more detailed list of specifications
   in addition to the required ones stated here.  Other codepoints MAY
   map to these same PHBs.  We refer to this set of codepoints as the
   Class Selector Codepoints, and the minimum requirements for PHBs that
   these codepoints may map to are called the Class Selector PHB
   Requirements.  The Class Selector Codepoints

   A specification of the packet forwarding treatments selected by the
   The DS field values of 'xxx000|xx', or DSCP = 'xxx000' and CU
   subfield unspecified, are reserved as a set of Class Selector
   Codepoints.  PHBs which are mapped to by these codepoints MUST
   satisfy the Class Selector PHB requirements in addition to preserving
   the Default PHB requirement on codepoint '000000' (Sec. 4.1).  The Class Selector PHB Requirements

   We refer to a Class Selector Codepoint with a larger numerical value
   than another Class Selector Codepoint as having a higher relative
   order while a Class Selector Codepoint with a smaller numerical value
   than another Class Selector Codepoint is said to have a lower
   relative order.  The set of PHBs mapped to by the eight Class
   Selector Codepoints MUST yield at least two independently forwarded
   classes of traffic, and PHBs selected by a Class Selector Codepoint
   SHOULD give packets a probability of timely forwarding that is not
   lower than that given to packets marked with a Class Selector
   codepoint of lower relative order, under reasonable operating
   conditions and traffic loads.  A discarded packet is considered to be
   an extreme case of untimely forwarding.  In addition, PHBs selected
   by codepoints '11x000' MUST give packets a preferential forwarding
   treatment by comparison to the PHB selected by codepoint '000000' to
   preserve the common usage of IP Precedence values '110' and '111' for
   routing traffic.

   Further, PHBs selected by distinct Class Selector Codepoints SHOULD
   be independently forwarded; that is, packets marked with different
   Class Selector Codepoints MAY be re-ordered.  A network node MAY
   enforce limits on the amount of the node's resources that can be
   utilized by each of these PHBs.

   PHB groups whose specification satisfy these requirements are
   referred to as Class Selector Compliant PHBs.

   The Class Selector PHB Requirements on codepoint '000000' are
   compatible with those listed for the Default PHB in Sec. 4.1.

So this patch pretty much just 'lifts' the bitfield definitions from this
RFC and incorporates them into the header in the same way that was previously
done for RFC-791 and TOS/Precedence to reflect the re-designation of
IPTOS_PREC_xxx that RFC 2474 incurred.

This reworking addresses the review comments:


2009-12-09  Philip Prindeville  <>

	* sysdeps/include/generic/netinet/ip.h: Add CSn definitions
	for ip_tos (per RFC 2474).



 sysdeps/generic/netinet/ip.h |   43 ++++++++++++++++++++++++++++++-----------
 1 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/sysdeps/generic/netinet/ip.h b/sysdeps/generic/netinet/ip.h
index 38bd755..a837b98 100644
--- a/sysdeps/generic/netinet/ip.h
+++ b/sysdeps/generic/netinet/ip.h
@@ -189,7 +189,26 @@ struct ip_timestamp
 #define	IPTOS_DSCP_EF		0xb8

- * Definitions for IP type of service (ip_tos)
+ * In RFC 2474, Section, the Class Selector Codepoints subsume
+ * the old ToS Precedence values.
+ */
+#define	IPTOS_CLASS_MASK		0xe0
+#define	IPTOS_CLASS(class)		((tos) & IPTOS_CLASS_MASK)
+#define	IPTOS_CLASS_CS0			0x00
+#define	IPTOS_CLASS_CS1			0x20
+#define	IPTOS_CLASS_CS2			0x40
+#define	IPTOS_CLASS_CS3			0x60
+#define	IPTOS_CLASS_CS4			0x80
+#define	IPTOS_CLASS_CS5			0xa0
+#define	IPTOS_CLASS_CS6			0xc0
+#define	IPTOS_CLASS_CS7			0xe0
+ * Definitions for IP type of service (ip_tos) [deprecated; use DSCP
+ * and CS definitions above instead.]
 #define	IPTOS_TOS_MASK		0x1E
 #define	IPTOS_TOS(tos)		((tos) & IPTOS_TOS_MASK)
@@ -200,18 +219,18 @@ struct ip_timestamp

- * Definitions for IP precedence (also in ip_tos) (hopefully unused)
+ * Definitions for IP precedence (also in ip_tos) [also deprecated.]
-#define	IPTOS_PREC_MASK			0xe0
-#define	IPTOS_PREC(tos)                ((tos) & IPTOS_PREC_MASK)
-#define	IPTOS_PREC_CRITIC_ECP		0xa0
-#define	IPTOS_PREC_FLASH		0x60
-#define	IPTOS_PREC_PRIORITY		0x20
-#define	IPTOS_PREC_ROUTINE		0x00
+#define	IPTOS_PREC(tos)			IPTOS_CLASS(tos)

  * Definitions for options.

Signed-off-by: Philip Prindeville <>

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