ICMP Message Formats 16 3 16 31 Type Code Checksum Type Code Checksum Unused Identifier Sequence Number IP Header +64 bits of original datagram Originate Timestamp (a)Destination Unreachable;Time Exceeded;Source Quench (e)Timestamp 0 16 31 16 31 Type Code Checksum Type Code Checksum Pointer Unused Identifier Sequence Number IP Header+64 bits of original datagram Originate Timestamp Receive Timestamp (b)Parameter Problem Transmit Timestamp (f)Timestamp Reply 0 8 16 31 Type Code Checksum Gateway Internet Address 16 31 IP Header +64 bits of original datagram Type Code Checksum (c)Redirect Identifier Sequence Number (g)Address Mask Request 8 16 31 Type Code Checksum 16 31 Identifier Sequence Number Type Code Checksum Optional data Identifier Sequence Number Address Mask (d)Echo,Echo Reply (h)Address Mask Reply ICMP Message Formats