TCP IP Illustrated

219573 640959 ack 38 sun slip icmp host aix 1000220503

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Unformatted text preview: 6 47 262.305086 ( 0.1463) slip.1035 > aix.echo: . ack 38 SLIP link brought down here slip.1035 > aix.echo: P 38:52(14) 458.155330 (195.8502) ack 38 sun > slip: icmp: host aix 458.156163 ( 0.0008) unreachable slip.1035 > aix.echo: P 38:52(14) 461.136904 (2.9807) ack 38 sun > slip: icmp: host aix 461.137826 (0.0009) unreachable slip.1035 > aix.echo: P 38:52(14) 467.136461 (5.9986) ack 38 sun > slip: icmp: host aix 467.137385 (0.0009) unreachable slip.1035 > aix.echo: P 38:52(14) 479.135811 ( 11.9984) ack 38 sun > slip: icmp: host aix 479.136647 ( 0.0008) unreachable slip.1035 > aix.echo: P 38:52(14) 503.134816 ( 23.9982) ack 38 sun > slip: icmp: host aix 503.135740 ( 0.0009) unreachabie 14 lines of output deleted here slip.1035 > aix.echo: P 38:52(14) 1000.219573 ( 64.0959) ack 38 sun > slip: icmp: host aix 1000.220503 ( 0.0009) unreachable slip.1035 > aix.echo: R 52:52(0) 1064.201281 ( 63.9808) ack 38 sun > slip: icmp: host aix 1064.202182 ( 0.0009) unreachable Figure 21.12 TCP handling of received ICMP host unreachable error. We type "another line" (line 3) and expect to see TCP time out and retransmit the message. Indeed, this line is sent six times before a reply is received. Lines 4-13 show the first transmission and the next four retransmissions, each of which generates an ICMP host unreachable from the router sun. "This is what we expect: the IP datagrams go from slip to the router bsdi (which has a default route that points to sun), and then to sun, where the broken link is detected. While these retransmissions are taking place, the SLIP link is brought back up, and the file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tcp_time.htm (25 of 29) [12/09/2001 14.47.27] Chapter 21. TCP Timeout and Retransmission retransmission on line 14 gets delivered. Line 15 is the echo from aix, and line 16 is the acknowledgment of the echo. This shows that TCP ignores the ICMP host unreachable errors and keeps retransmitting. We...
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