Messages in this thread | | | Subject | Re: How to survive in a Micro$oft environment?? | Date | Sun, 27 Feb 2000 16:42:20 +0000 (GMT) | From | Alan Cox <> |
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> as a gateway probe. The latter is basically a traceroute packet to > sunsite.unc.edu or tsx-12.mit.edu, with a TTL of 2 (this usually elicts > an ICMP redirect and/or a time exceeded, from which we can piece together > the gateway's IP).
The gateway probe is tricky. You may start routing through one of the millions of machines erroneously shipped by vendors with routing enabled or via the wrong router. There is a router discovery protocol. Its less supported but a lot safer. Listening for OSPF/RIP/RIP2 can also do the detection sometimes.
Its probably not that big an issue but if you install a network of machines that accidentally all choose to route via the tiny isdn router on the edge of the lan not via the main router bad things occur.
At the minimum you need to verify that the icmp time exceeded comes from a host which you cannot directly reach. If you can directly reach the 2nd or 3rd hop that errors then you have found a secondary host misconfigured as router, or a secondary router, and it just told you the correct router to use. Sometimes you'll get a redirect, sometimes you dont.
If its an older 3com office connect firmware you actually start crashing the 3com box even ;)
Alan
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