when you tracert a certain website, who is responsible if in the 4th or 5th hop there is a request time out until it failed or even if it is successful? is it in the ISP or the WWW link already?
It depends, but usually the previous hop owner is in some way responsible, or can find someone who is responsible.
If the trace is successful after that hop, then I wouldn't worry about that one hop. I would only mean that the router in question doesn't respond to icmp or udp traceroutes, or that it is using an RFC 1918 address (which is not really a good practice, but does happen... my connection passes through 3 private hops at the ISP before hitting a public hop. I can trace out just fine, but can't trace to my network... annoying, but not really a problem.)
If the trace fails, and the site is unaccessible, then contact your provider and see if they can find someone to resolve the problem.
It is difficult to get issues like this resolved if you or your provider don't have direct connections to the failed router in question, but many times they resolve themselves as it can mean a much bigger issue that the ISP/Transit provider in question already knows about and is working on it.
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