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Accepted
vaab
Asked: 2013-12-29 20:14:40 +0800 CST

Network debugging port 25 timeout on dedicated server

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I have hosta and hostb, two dedicated server in the same area (same bay?).

Ping and communication towards these hosts are okay. But hosta seems to have all its outgoing communications on port 25 blocked somehow:

With nc working-smtp 25 (and and port 80) on both hosts. I figured that:

  • hosta has all it's outgoing communication timeouted on port 25 only.
  • hostb work fine.

Note that working-smtp is a working smtp server unrelated to both of them, practical to make test (and where I have put a tcpdump to double check connections.)

BTW, both hosts can ping working-smtp.

So I did a traceroute -p 25 -T working-smtp, and first two server in both traceroute are EXACTLY the same:

# traceroute -p 25 -T working-server
traceroute to working-server (xx.xx.xx.xx), 30 hops max, 60 byte packets
 1  A (xx.xx.xx.xx)  0.363 ms * *
 2  B (xx.xx.xx.xx)  0.819 ms  1.063 ms  1.166 ms
...

(A and B are network gateways out of my control from the dedicated bay.)

  • On hosta, the next hops are * * * until it reaches max hop number.
  • On hostb, the next hops are all valued and it reaches working-server in 6 hops.

If I do the same traceroute with port 80, both server reaches the target with the same track.

What conclusion could we draw ? Is there more test to do ? Should I contact my dedicated server provider ?

networking

1 Answers

  1. Best Answer

    I echo others' sentiments, that the hosting provider should be squarely in the line of enquiry (though as PressingOnAlways notes above, it'd also be worth confirming there are no outbound firewall rules in effect on hosta). I think you've done an excellent investigation here (+1 from me!) and until the provider clarifies their position, there's not much more to say.

    It would be fairly normal for hosting providers to block outbound connections to mail servers. Some will want you to use their mail server as an intermediate hop, others will remove the block on a source-host-by-source-host basis on request (though they may ask you to explicitly accept an AUP first, to prevent their address space being used for hosting bulk senders).

    I'm only posting this as an answer because your original question as written only admits of two answers - "yes" and "no" - and if it doesn't get an example of each, it'll stay unanswered, floating around like some kind of ghost ship, forever.

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