TCP IP Illustrated

33593 netb33438 udp 12 ttl 2 optlen16 ssrrgateway

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Unformatted text preview: =16 SSRR(#gateway gabby westgate} EOL) netb > sun: icmp: time exceeded intransit sun.33593 > netb.33438: udp 12 (ttl 2, optlen=16 SSRR(#gateway gabby westgate} EOL) gateway > sun: icmp: time exceeded intransit sun.33593 > netb.33439: udp 12 (ttl 2, optlen=16 SSRR{#gateway gabby westgate} EOL) gateway > sun: icmp: time exceeded intransit sun.33593 > netb.33440: udp 12 (ttl 2, optlen=16 SSRR(#gateway gabby westgate} EOL) gateway > sun: icmp: time exceeded intransit sun.33593 > netb.33441: udp 12 (ttl 3, optlen=16 SSRR{#gateway gabby westgate} EOL) gateway > sun: icmp: gateway unreachable - source route failed sun.33593 > netb.33442: udp 12 (ttl 3, optlen=16 SSRR{#gateway gabby westgate} EOL) file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tracerou.htm (14 of 17) [12/09/2001 14.46.48] Traceroute Program 16 6.876579 (5.0013) 17 7.110518 (0.2339) sun.33593 > netb.33443: udp 12 (ttl 3, optlen=16 SSRR{#gateway gabby westgate} EOL) gateway > sun: icmp: gateway unreachable - source route failed Figure 8.10 tcpdump output of traceroute with failed strict source route. First note that each UDP datagram sent by sun has a destination of netb, not the destination host (westgate). We described this with the example shown in Figure 8.7. Similarly, the other two routers specified with the -G option (gateway and gabby) and the final destination (westgate) become the SSRR option list on the first hop. We can also see from this output that the timeout used by traceroute (the time difference between lines 15 and 16) is 5 seconds. traceroute Round Trips with Loose Source Routing Earlier we said that there is no guarantee that the route from A to Bis the same as the route from B to A. Other than having a login on both systems and running traceroute on each end, it's hard to find out if there is a difference in the two paths. Using loose source routing, however, we can determine the route in both directions. The trick is to spe...
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