Option Flags
This section describes the flags for the Options field, defined in RFC 2186. Some experimental option flags are discussed in Section B.4. The flag’s hexadecimal value appears in parentheses following its name.
- ICP_FLAG_HIT_OBJ (0x80000000)
When this flag is set in an ICP query, it indicates that the sender supports the HIT_OBJ feature (see Section 8.1.2.3).
- ICP_FLAG_SRC_RTT (0x40000000)
This option is used to include network round-trip time measurements in ICP replies (see Section 8.1.2.4). The ICP_FLAG_SRC_RTT bit is set in the ICP query message to indicate that the sender would like to receive the neighbor’s RTT measurement to the origin server. If the recipient has a measured value, it includes the RTT in the low 16 bits of the Option Data field and sets the ICP_FLAG_SRC_RTT bit in the reply. The RTT value is encoded as a 16-bit integer in milliseconds.
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