O'Reilly logo

Cisco LAN Switching Fundamentals by Basir Sakandar - CCIE No. 6040, David Barnes - CCIE No. 6563

Stay ahead with the world's most comprehensive technology and business learning platform.

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, tutorials, and more.

Start Free Trial

No credit card required

Type of Service

To give priority for traffic at Layer 3, type of service (ToS), or now known as the DS byte, needs to be manipulated. The ToS field is composed of 1 byte in the IP packet. IP precedence is the three most significant bits. As a result, a total of 8 different types of priorities are found in IP precedence. Types 6 and 7 are used by control traffic.

The Differentiated Services Code Point (DSCP) uses the first 6 bits of ToS byte rather than the original 3 as mentioned, which can provide up to 64 different types of priorities. DSCP is backward compatible to IP precedence as the mapping shows in Example 8-1.

Example 8-1. ToS to DSCP Map
 IP Precedence 0 =0 DSCP IP Precedence 1 =8 DSCP IP Precedence 2 =16 DSCP IP Precedence 3 =24 DSCP ...

With Safari, you learn the way you learn best. Get unlimited access to videos, live online training, learning paths, books, interactive tutorials, and more.

Start Free Trial

No credit card required