Differentiate Services Code Point Support

$Id: dscp,v 1.1.2.1 2012/02/24 05:20:36 marka Exp $

Differentiate Services Code Point (DSCP) is implemented in IPv4 using the

TOS octet and in IPv6 using the TCLASS octet.

RFC 3542 defines the api to manipulate the TCLASS octet as part of

the advanced socket API. TCLASS is settable on both a socket and

packet basis (setsockopt/sendmsg) and the sent value can be retrieved

using recvmsg over UDP. Retrieval is undefined for TCP.

The Advanced socket API was not incorporated into the POSIX socket

API for IPv6 and may not be completely implemented in any OS.

For TOS setsockopt() supports setting of the field on a persocket

basis. TOS may also be set on a per packet basis on some OS using

sendmsg. If it is not supported the sendmsg call reports a error.

Support can only be determined by attempted to send a packet with

the option set. Retrieval of the sent TOS value is retrievable on

Linux. This can be determined at compile time.

DSCP values need to be compatible with TOS values as it is a re-use

of the field.

LIBISC:

We will need to be able to probe for the level of DSCP support. We

need to know if we can set it at the socket level, packet level and

if we can retrieve the DSCP value sent. This needs to be done

independently for IPv4 and IPv6.

#define ISC_NET_DSCPRECVV4 0x01 /* Can receive sent DSCP value IPv4 */

#define ISC_NET_DSCPRECVV6 0x02 /* Can receive sent DSCP value IPv6 */

#define ISC_NET_DSCPSETV4 0x04 /* Can set DSCP on socket IPv4 */

#define ISC_NET_DSCPSETV6 0x08 /* Can set DSCP on socket IPv6 */

#define ISC_NET_DSCPPKTV4 0x10 /* Can set DSCP on per packet IPv4 */

#define ISC_NET_DSCPPKTV6 0x20 /* Can set DSCP on per packet IPv6 */

#define ISC_NET_DSCPALL 0x3f /* All valid flags */

unsigned int

isc_net_probedscp(void);

/*%<

* Probe the level of DSCP support.

*/

We also need to be able to set DSCP values on a per socket basis, per packet

basis and to retrieve dscp values from received packet.

Setting dscp on a per socket basis shall be done using isc_socket_dscp.

void

isc_socket_dscp(isc_socket_t *sock, unsigned int dscp);

/*%<

* Requires:

*\li 'sock' is a valid socket.

*/

/*@}*/

isc_socketevent shall be extended to support the sending of and retrieval

of DSCP values. If ISC_SOCKEVENTATTR_DSCP is set then isc_socket_sendto2

shall set the DSCP value. isc_socket_recv shall set ISC_SOCKEVENTATTR_DSCP

and the dscp element if the OS returns the value via recvmsg.

#define ISC_SOCKEVENTATTR_DSCP 0x00040000U /* public */

struct isc_socketevent {

ISC_EVENT_COMMON(isc_socketevent_t);

isc_result_t result; /*%< OK, EOF, whatever else */

unsigned int minimum; /*%< minimum i/o for event */

unsigned int n; /*%< bytes read or written */

unsigned int offset; /*%< offset into buffer list */

isc_region_t region; /*%< for single-buffer i/o */

isc_bufferlist_t bufferlist; /*%< list of buffers */

isc_sockaddr_t address; /*%< source address */

isc_time_t timestamp; /*%< timestamp of packet recv */

struct in6_pktinfo pktinfo; /*%< ipv6 pktinfo */

isc_uint32_t attributes; /*%< see below */

isc_eventdestructor_t destroy; /*%< original destructor */

unsigned int dscp; /*%< UDP dscp value */

};

A convience function will be provided to allocate and intialize the structure.

isc_socketevent_t *

isc_socket_socketevent(isc_socket_t *sock0, isc_eventtype_t eventtype,

isc_taskaction_t action, const void *arg)

NAMED/LIBDNS:

Named needs to be able to set the DSCP value of sent traffic. We should

be able to set DSCP for all TCP connections.

For UDP we should have a default DSCP value for when we can't set this on

a per packet basis with the ability to override for specific destinations.

options/view/server;

tcp-dscp <value>;

udp-dscp <value>;

http://bogpeople.com/networking/dscp.shtml list a set of TOS compatible

values (below).

DSCP Name DS Field Value IP Precedence

Binary Decimal

CS0 000 000 0 0

CS1 001 000 8 1

AF11 001 010 10 1

AF12 001 100 12 1

AF13 001 110 14 1

CS2 010 000 16 2

AF21 010 010 18 2

AF22 010 100 20 2

AF23 010 110 22 2

CS3 011 000 24 3

AF31 011 010 26 3

AF32 011 100 28 3

AF33 011 110 30 3

CS4 100 000 32 4

AF41 100 010 34 4

AF42 100 100 36 4

AF43 100 110 38 4

CS5 101 000 40 5

EF 101 110 46 5

CS6 110 000 48 6

CS7 111 000 56 7

CS Class Selector (RFC 2474)

AFxy Assured Forwarding (x=class, y=drop precedence) (RFC2597)

EF Expedited Forwarding (RFC 3246)

value should be one of these or a numeric 0..63. The default value is 0.