How many traffic classes does IPv6's Traffic Class field support for QoS?

How many traffic classes does IPv6's Traffic Class field support for QoS?

• A. 128
• B. 64
• C. 256
• D. 16

Answer: (C)

IPv6’s Traffic Class field is 8 bits wide, which means it can carry 2^8, or 256, distinct values. These values are used to indicate how packets should be treated for quality of service. In practice, QoS is often implemented by using the top 6 bits as the Differentiated Services Code Point (DSCP), giving 64 DSCP codepoints, while the bottom 2 bits carry ECN flags. But the field itself enables 256 possible patterns, so the number of traffic classes it supports is 256.

IPv6’s Traffic Class field is 8 bits wide, which means it can carry 2^8, or 256, distinct values. These values are used to indicate how packets should be treated for quality of service. In practice, QoS is often implemented by using the top 6 bits as the Differentiated Services Code Point (DSCP), giving 64 DSCP codepoints, while the bottom 2 bits carry ECN flags. But the field itself enables 256 possible patterns, so the number of traffic classes it supports is 256.