TCP IP Illustrated

Figure 612 is a redo of figure 63 showing the

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Unformatted text preview: he kernel. If the final column specifies "user process", then that message is passed to all user processes that have registered with the kernel to read received ICMP messages. If there are none of these user processes, the message is silently discarded. (These user processes also receive a copy of all the other ICMP messages, even those handled by the kernel, but only after the kernel has processed the message.) Some messages are completely ignored. Finally, if the final column is a string in quotes, that is the Unix error message corresponding to that condition. Some of these errors, such as TCP's handling of a source quench, we'll cover in later chapters. type code 0 0 Description echo reply Handled by user process file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/icmp_int.htm (14 of 16) [12/09/2001 14.46.43] Chapter 6. ICMP: Internet Control Message Protocol 3 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 destination unreachable: network unreachable host unreachable protocol unreachable port unreachable fragmentation needed but DF bit set source route failed destination network unknown destination host unknown source host isolated (obsolete) dest. network administratively prohibited dest. host administratively prohibited network unreachable for TOS host unreachable for TOS communication administratively prohibited host precedence violation precedence cutoff in effect "No route to host" "No route to host" "Connection refused" "Connection refused" "Message too long" "No route to host" "No route to host" "No route to host" "No route to host" "No route to host" "No route to host" "No route to host" "No route to host" (ignored) (ignored) (ignored) 0 source quench kernel for TCP, ignored by UDP 5 0 1 2 3 redirect: redirect for network redirect for host redirect for type-of-service and network redirect for type-of-service and host kernel updates routing table kernel updates routing table kernel updates routing table kernel updates routing table 8 0 echo request kernel generates reply 9 10 0 0 router advertisement router solicitation user process user process 11 0 1 time exceeded: TTL equals 0 during transit TTL equals 0 during reassembly user process user process 12 0 1 parameter problem: IP header bad (catchall error) required option missing "Protocol not available" "Prot...
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