Knowledge Base

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Network connections

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1. Traceroutes to routers

Traceroutes sent to a router should not be expected to respond to the "destination unreachable" probe. This error is an error that the destination host that is requested is supposed to respond with. This is when traceroute, or any other form of traceroute, terminates. All other routers and such in between the originating and destination hosts, just move the packet along after stripping of a TTL bit, or error'ng out at the next hop when the TTL has been reached.

Most all routers do not consider the destination unreachable message a priority to respond to. Which makes sense if you don't want your router to be bombarded with bogus ports to take the router down. i.e. a Denial of Service (DoS) attack. Here are some example of tracerouting through a router then to a router.

Through multiple routers:

traceroute to yahoo.com (204.71.200.245), 30 hops max, 40 byte packets
1 209.239.32.1 (209.239.32.1) 1.508 ms 1.233 ms 3.596 ms
2 209.201.44.9 (209.201.44.9) 1.400 ms 1.546 ms 0.978 ms
3 Serial4-1-0.core2.dca1.IConNet.NET (204.245.69.194) 2.591 ms 2.451ms 2.567 ms
4 POS6-0-0.peer1.dca1.IConNet.NET (204.245.71.10) 3.186 ms 2.528 ms3.473 ms
5 fddi3-0.cr1.dca.globalcenter.net (192.41.177.113) 8.625 ms 7.854ms 7.292 ms
6 fe2-0-0.br1.DCA.globalcenter.net (204.152.166.13) 4.435 ms 4.077 ms 10.195 ms

To router 204.245.71.10:

traceroute to 204.245.71.10 (204.245.71.10), 30 hops max, 40 byte
packets
1 209.239.32.1 (209.239.32.1) 1.391 ms 1.409 ms 1.473 ms
2 209.201.44.9 (209.201.44.9) 2.258 ms 0.741 ms 3.064 ms
3 Serial4-1-0.core2.dca1.IConNet.NET (204.245.69.194) 3.321 ms 4.426ms 3.132 ms
4 POS6-0-0.peer1.dca1.IConNet.NET (204.245.71.10) 5.052 ms * 2.714ms

To router 192.41.177.118:

traceroute to 204.152.166.13 (204.152.166.13), 30 hops max, 40 byte
packets
1 209.239.32.1 (209.239.32.1) 16.559 ms 1.286 ms 0.932 ms
2 209.201.44.9 (209.201.44.9) 1.646 ms 3.230 ms 2.976 ms
3 Hssi12-0-0.core1.dca1.IConNet.NET (204.245.69.50) 2.678 ms 2.879ms 3.101 ms
4 POS0-0-0.peer1.dca1.IConNet.NET (204.245.71.6) 3.332 ms 5.094 ms2.615 ms
5 fddi2-1-0.br1.dca.globalcenter.net (192.41.177.118) 21.116 ms * *

Bottom line is if a client is using our router as an example, we can only consider the mili-seconds it took not the timeouts. So this does not make for a good traceroute to troubleshoot with. We must traceroute through the routers to find connections that are slow or that are broken.


Updated: January 4, 2001

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