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Internet Control Message Protocol (ICMP). ICMP. Internet Control Message Protocol IP is the delivery standard at the TCP/IP internet layer ICMP is the standard for supervisory messages. ICMP. Internet Control Message Protocol
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ICMP • Internet Control Message Protocol • IP is the delivery standard at the TCP/IP internet layer • ICMP is the standard for supervisory messages
ICMP • Internet Control Message Protocol • IP and ICMP are designed to work together. Even have adjacent RFC (standard) numbers • ICMP PDU is carried in the information field of an IP packet IP Header ICMP PDU
ICMP • Several ICMP Message Types • Error messages warn of problems • Not error correction, because there is no transmission of lost or damaged packets B Error Message C A
ICMP • Several ICMP Message Types • Query asks host if it is active • Also called “Echo” and “Ping” B Query Request C A Query Response
ICMP • Several ICMP Message Types • Flow control: Source quench message asks other side to slow down B Source Quench C A
Source Quench • Weak form of flow control • When host sending packets gets source quench, it slows down • If another source quench message arrives, slows down even more • If source quench messages stop, slowly increases speed
ICMP • Redirection • Host uses a particular router (B) • Router B tells host to use a different router (A) for that destination host in the future Router A IP Packet Redirection: “Next time, use Router A for this destination host” Router B Host X