IPv4 ToS Byte: True Statements
Question
Which two statements about the IPv4 ToS byte are true? (Choose two.)
Answers
Explanations
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A. B. C. D. E.BE.
The correct answers are B and E.
Explanation:
The Type of Service (ToS) byte is a field in the IPv4 header that specifies the level of service and priority assigned to an IP packet. The ToS byte is located in the Layer 3 header.
A. The ToS byte is located in the Layer 2 header. This statement is false. The Layer 2 header does not have a ToS byte. It has fields for source and destination MAC addresses, the EtherType, and other protocol-specific information.
B. The ToS byte is located in the Layer 3 header. This statement is true. The ToS byte is part of the IPv4 header, which is a Layer 3 protocol.
C. The DSCP values range from 0 to 7. This statement is false. The DSCP (Differentiated Services Code Point) values range from 0 to 63, which allows for a finer granularity of service differentiation.
D. The IP precedence and the DSCP fields have two overlapping bits. This statement is true. The first three bits of the DSCP field are the same as the IP precedence field, which was used in older versions of the IP protocol to indicate the priority of a packet.
E. The class selector in the DSCP field is defined for backward compatibility with IP precedence. This statement is true. The class selector is a set of 8 DSCP values that correspond to the 8 possible IP precedence values. It allows older network equipment that supports only IP precedence to still provide some level of service differentiation based on packet priority.
