Tos Field - HP 7102dl - ProCurve Secure Router Configuration Manual

Setting Up Quality of Service
Overview
8-6
However, neither IP precedence nor DiffServ addresses the second issue: how
a router actually provides differentiated service. You must configure other
protocols to provide the service requested by the ToS value. You can configure
the ProCurve Secure Router to:
grant traffic with a higher IP precedence value relatively more bandwidth
using WFQ
grant a class of traffic (which can be defined by ToS value or other criteria)
a certain amount of an interface's bandwidth
place traffic into a first-served queue that is guaranteed a certain trans-
mission rate (LLQ)

ToS Field

The IPv4 header includes an 8-bit ToS field, which allows you to mark traffic
for special handling. Two standards define how the ToS field defines traffic:
IP precedence, the original standard for using this field, and DiffServ, which
was introduced in 1998 with the Request for Comments (RFC) 2474. (See http:/
/www.ietf.org/rfc/rfc2474.txt for more information.)
IP Precedence. IP precedence includes two subfields—a three-bit prece-
dence field used for prioritization and a four-bit subfield for the specific type
of service. The remaining bit is unused.
You can mark seven priority traffic classes in the three-bit precedence field.
Packets for which this field is unmarked (IP precedence 0) receive routine
handling. Traffic with an IP precedence value of 1 takes simple priority over
routine traffic. Traffic with an IP precedence value of 2 has an immediate
priority, a value of 3 has a flash priority, and a value of 4 has a flash override
priority. The highest user-defined value is 5, which has critical priority.
Values 6 and 7 are reserved for Internet and network use, ensuring that routing
updates and other network traffic receive a higher priority than user-generated
traffic. Because routes must be accurate to ensure delivery of other traffic,
routing traffic must receive priority treatment. Value 6 is designed for use
between networks, and it should only be implemented by gateway devices.
Value 7 is for private network use; organizations should determine themselves
what type of service IP precedence 7 implies and for what types of traffic it
should be assigned.