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Unformatted text preview: he pound sign (#) denotes the pointer field, which assumes the values of 4, 8,
12, and 16. The length field will always be 15 (three IP addresses plus 3 bytes of overhead).
Notice how the destination address of the IP datagram changes on every hop.
When an application receives data that was source routed, it should fetch the value of the
received route and supply a reversed route for sending replies.
The Host Requirements RFC specifies that a TCP client must be able to specify a source
route, and that a TCP server must be able to receive a source route, and use the reverse route
for all segments on that TCP connection. If the TCP server later receives a different source
route, that newer source route overrides the earlier one.
traceroute Examples with Loose Source Routing
The -g option to traceroute lets us specify intermediate routers to be used with loose
source routing. This option can be specified up to eight times. (The reason this is eight and
not nine is that the programming interface being used requires that the final entry be the
Recall from Figure 8.4 that the route to the NIC, nic.ddn.mil, was through the NASA
Science Internet. In Figure 8.8 we force the datagrams to pass through the NSFNET instead
by specifying the router enssl42.UT.westnet.net (220.127.116.11) as an intermediate
sun % traceroute -g 18.104.22.168 nic.ddn.mil
traceroute to nic.ddn.mil (22.214.171.124), 30 hops max, 40
1 netb.tuc.noao.edu (126.96.36.199) 259 ms 256 ms 235 ms
2 butch.telcom.arizona.edu (188.8.131.52) 234 ms 228 ms 234
3 Gabby.Telcom.Arizona.EDU (184.108.40.206) 234 ms 257 ms 233
4 enssl42.UT.westnet.net (220.127.116.11) 294 ms 288 ms 295 ms
5 t3-2.Denver-cnss97.t3.ans.net (18.104.22.168) 294 ms 286 ms
6 t3-3.Denver-cnss96.t3.ans.net (22.214.171.124) 293 ms 288 ms
7 t3-1.St-Louis-cnss80.t3.ans.net (126.96.36.199) 294 ms 318
ms 294 ms
8 * t3-1.Chicago-cnss24.t3.ans.net (188.8.131.52) 318 ms 295
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12