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Getting access to some Internet sites

By Shanghai Sam ·
Starting a few weeks ago I started having problems gaining access to a number of Internet sites. I am able to get to a great number of sites, but some get with no problem.
These sites time out. I can do a nslookup to these sites and get there ip address. When I do a traceroute, the trace will not continue after 8 or more hops and will give several lines of "* * *". When I do a "wget" it will not connect. Some of the sites that I am not able to get is zdnet.com and careerbuilders.com.
Can anyone tell me what my problem may be?

Thanks

Dale

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Getting access to some Internet sites

by Shanghai Sam In reply to Getting access to some In ...

Hi,
network timeouts such as the one you describe are caused by routing problems. Tracert works by manipulating the 'time to live' values of ping packets. by default the time to live on a ping is 128, every time the packet is passed from router to router the number is decremented by one. When the number reaches 0 (IE it has passed through 128 odd routers) the router that receives it at that value sends back an error - this is to stop your packet endlessly looping round the world. Nslookup sends out a series of pings (30 by default) one at a time. it sets the ttl on the first packet to (I think) 0, therefore the first router it hits (your gateway) returns it with a timed out message. Nslookup displays the ip address of the router that returned the packet, then sends out another ping with a ttl of 1, this hits your first router, which decrements the ttl to 0 and passes it on to the next router. this sees that the ttl is 0 and sends back a request timed out, the result of which is displayed to you by nslookup which then sends another ping with a ttl of 2 - and son and so on up to a max of 30 'hops'. ping \ tracert also keep track of how long it's been since they sent a packet out, and if it exceeds a preset timeout period without a reply they will flag a 'request timed out' error. That's just a bit of background info to lead us on to what is happening to you. When your packet is reaching the 8th + router, that router is passing it on to the router shown in it's list as the best route to your destination address. As the ip protocol is 'connectionless' it doesn't check to see if the next router actually gets it, it just passes it on and leaves it up to the next router to communicate with you if needs be.

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Getting access to some Internet sites

by BeerMonster In reply to Getting access to some In ...

....continued (won't give me the option of posting a comment for some reason)

the Problem here is that the next router in the list either isn't working properly or isn't working at all. Your packet is either going into a 'dead end' or is being ignored by the malfunctioning router (although routers are supposed to keep tabs on their neighbours, this is not always effective. The responsibility for this lies with your network provider \ ISP. You will need to contact them, along with the resultsof the tracert, and ask them to look into it. Chances are that they will already be aware of the problem, unless you are the only person using their network they are probably on the phone right now to irate customers. Hope this helps....

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Getting access to some Internet sites

by rossiter In reply to Getting access to some In ...

You could try running traceroute with the -I option. This tells tracroute to send ICMP packets instead of UDP packets. Sometimes sending ICMP packets will clear up the * * * you see when you hop over certain routers.

HTH,
Eric

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