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| Subject: | Re: Traceroute question |
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| Date: | Thu, 28 Dec 2006 04:40:48 -0500 |
On Wed, Dec 27, 2006 at 05:36:58PM -0800, Becky Nelson wrote:
I am running a traceroute and have two hops that report the same address. Could someone please explain what would cause this? I suspect that this is some type of firewall?
There are a number of things that can cause this, but the most common is a buggy IP implementation on the first router, which it forwards packets with a ttl=0. http://www.freesoft.org/CIE/Topics/54.htm [snip] Buggy TCP/IP implementations Traceroute depends on a rather obscure feature that often doesn't work correctly. Some of the problems people have found: code that fails to decrement TTL, code that incorrectly forwards packets with zero TTL, code that does not generate ICMP Timeouts, and code that sends ICMPs with the same TTL as the original packet. This last problem, of course, results in our ICMP Timeouts being sent with zero TTL - guaranteed not to make it back to us.
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