This preview shows page 1. Sign up to view the full content.
Unformatted text preview: igini/Docu...homenet2run/tcpip/tcp-ip-illustrated/tracerou.htm (11 of 17) [12/09/2001 14.46.48] Traceroute Program 9 t3-2.Cleveland-cnss40.t3.ans.net (220.127.116.11) 319 ms 318
ms 324 ms
10 t3-1.New-York-cnss32.t3.ans.net (18.104.22.168) 324 ms 318
ms 324 ms
11 t3-1.Washington-DC-cnss56.t3.ans.net (22.214.171.124) 353 ms
348 ms 325 ms
12 t3-0.Washington-DC-cnss58.t3.ans.net (126.96.36.199) 348 ms
347 ms 325 ms
13 13-0. enssl45.t3.ans. net (188.8.131.52) 353 ms 348 ms
14 nsn-FIX-pe.sura.net (184.108.40.206) 353 ms 348 ms 325 ms
15 GSI.NSN.NASA.GOV (220.127.116.11) 353 ms 348 ms 354 ms
16 NIC.DDN.MIL (18.104.22.168) 354 ms 347 ms 354 ms
Figure 8.8 traceroute to nic.ddn.mil with a loose source route through the
This time there appear to be 16 hops with an average RTT of around 350 ms, while the
normal route shown in Figure 8.4 had only 13 hops and an average RTT of around 322 ms.
The default route appears better. (There are also other decisions made when routes are
established. Some are made on the basis of the organizational and political boundaries of
the networks involved.)
But we said there appear to be 16 hops, because a comparison of this output with our
previous example through the NSFNET (Figure 8.5) shows three missing routers in this
example using loose source routing. (These are probably caused by bugs in the router's
generation of ICMP time exceeded errors in response to source routed datagrams.) The
router gateway.tuc.noao.edu is missing between netb and butch, and the routers
Westgate.Telcom.Arizona.edu and uu-ua.AZ.westnet.net are also missing
between Gabby and enssl42.UT.westnet.net. There is probably a software problem in these
missing routers related to incoming datagrams with the loose source routing option. There
are really 19 hops between the source and the NIC, when using the NSFNET. Exercise 8.5
continues the discussion of these missing routers.
This example also illustrates another problem. On the command line we have to specify the
dotted-decimal IP address of the router enssl42.UT.westnet.net instead of it...
View Full Document
- Spring '12