Pertemuan 18 TCP/IP Suite Control Messages 1 Discussion Topics • • • • • • • • Introduction to control messages CMP redirect/change requests Clock synchronization and transit time estimation Information requests and reply message formats Address mask requirements Router discovery message Router solicitation message Congestion and flow control messages 2 ICMP Redirect/Change Requests The default gateway of the host may need to use a redirect/change request to inform the host of the best path to a certain network. Clock Synchronization and Transit Time Estimation • The ICMP timestamp request message allows a host to ask for the current time according to the remote host. • The remote host uses an ICMP timestamp reply message to respond to the request. Address Mask Requirements • When a network administrator uses the process of subnetting to divide a major IP address into multiple subnets, a new subnet mask is created. Router Discovery Message • When a host on the network boots, and the host has not been manually configured with a default gateway, it can learn of available routers through the process of router discovery. Router Solicitation Message • A host generates an ICMP router solicitation message in response to a missing default gateway. Congestion and Flow Control Messages ICMP source-quench messages are used to reduce the amount of data lost from congestion.