When I traceroute any website the first IP after the ISP gateway is a private range one (10.1.74.xx). Is it normal? Can it cause any problems (problems for Postfix delivering messages for example)?


It's not abnormal or normal - all of the hops in between your host and the final destination are invisible to the actual packets. All they care about is end to end reachability. It sounds like you're having another problem, perhaps? But to answer your question, no, in and of itself, it doesn't cause any problems.

  • Yes, you are right - I have another problem: Postfix can not deliver messages to servers outside my country, it can deliver just to those that are inside the country. And the only difference between the outside and the inside ones I see is that the traceroute to outside servers is going through 10.1.74.xx but to inside ones not. I contacted my ISP and they told me that they do not block/filter anything, and the only thing they suggested is that I need a PTR record (which can not be the problem). – JohnZ Aug 5 '11 at 13:13
  • Ok, well instead of going Q&A in comments, lets accept this one, and please ask another question with a lot more details about your configuration, what country you're in, a abnormal vs normal traceroute, exactly what you mean by 'can not deliver' (no TCP connection? bounce?) and we'll go from there. – Aaron Aug 5 '11 at 13:20
  • Actually, private addresses emitting control packets can cause a variety of problems, and is indicative of (at least) an incompetent network admin. – womble Aug 5 '11 at 13:51
  • @womble: If you go for private IPs on you backbone links (something that used to be recommended, to preserve IPv4 space), you will want to leak a small subset of control packets from them (TTL exceeded, Fragmentation needed, possibly a few more). – Vatine Aug 5 '11 at 14:12

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