TCP IP Illustrated

Ack ack ack slip1056 vangoghecho ack 9 sun slip

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Unformatted text preview: rom our host slip through our dialup SLIP link to the host vangogh.cs.berkeley.edu, and then take the link down. First, here is the interactive output: slip % sock -K vangogh.cs.berkeley.edu echo we type this line testing and see it echoed testing sometime in here the dialup SLIP link is taken down read error: No route to host Figure 23.3 shows the tcpdump output that was collected on the router bsdi. (The connection establishment and window advertisements have been removed.) 1 0.0 2 0.277669 0.424423 3 0.2777) 0.1468) 4 5 6 7 8 7200.818081 (7200.3937) 7201.243046 ( 0.4250) 14400.688106 (7199.4451) 14400.689261 ( 0.0012) 14475.684360 ( 74.9951) slip.1056 > vangogh.echo: P ack 1 vangogh.echo > slip.1056: P ack 9 slip. 1056 > vangogh. echo: 9 slip. 1056 > vangogh. echo: 9 vangogh, echo > slip. 1056: 9 1:9(8) 1:9(8) . ack . ack . ack slip.1056 > vangogh.echo: . ack 9 sun > slip: icmp; net vangogh unreachable slip. 1056 > vangogh. echo: . ack 9 file:///D|/Documents%20and%20Settings/bigini/Docum.../homenet2run/tcpip/tcp-ip-illustrated/tcp_keep.htm (7 of 9) [12/09/2001 14.47.30] Chapter 23. TCP Keepalive Timer 9 24 25 14475.685504 ( 0.0011) 15075.759603 (75.1008) 15075.760761 ( 0.0012) sun > slip: icmp: net vangogh unreachable 14 lines deleted slip.1056 > vangogh.echo: R 9:9(0) ack 9 sun > slip: icmp: net vangogh unreachable Figure 23.3 Keepalive example when other end is unreachable. We start the example the same as before: lines 1-3 verify that the connection is up. The first keepalive probe 2 hours later is fine (lines 4 and 5), but before the next one occurs in another 2 hours, we bring down the SLIP connection between the routers sun and netb. (Refer to the inside front cover for the topology.) The keepalive probe in line 6 elicits an ICMP network unreachable from the router sun. As we described in Section 21.10, this is just a soft error to the receiving TCP on the host slip. It records that the ICMP error was received, but the receipt of the error does not take down the connection. Nine more keepali...
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