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Thread: telnet connection delay

  1. #11
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    Default Re: telnet connection delay

    Please Tony, read above why we use this DNS lookup. It is only to find out of a (any) reversed lookup gives an uwanted delay as encoutered in the OPs telnet session. If there is a answer or a "not found" is of no importance here.
    Henk van Velden

  2. #12
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    Default Re: telnet connection delay

    Quote Originally Posted by hcvv View Post
    Please Tony, read above why we use this DNS lookup. It is only to find out of a (any) reversed lookup gives an uwanted delay as encoutered in the OPs telnet session. If there is a answer or a "not found" is of no importance here.
    Ok,
    Then consider my post 2 separate responses...

    The warning about running telnet server is based entirely on the very first post.
    The part about doing a reverse lookup, I'm not clear what you were trying to investigate, machines fundamentally communicate by MAC address and on top of that the IP address... Machines don't actually communicate by name so names have to be resolved to IP addresses... but the reverse isn't typically true. Bottom line, a reverse lookup wouldn't happen for an attempted telnet connection, reverse lookups are useful only for more complex analytical applications, not simple network connections.

    Typically, latencies for simple connections like telnet are network related, typically not system.
    So, recommend using the most obvious tool for initially testing latency... PING and if you're traversing multiple routers, traceroute.

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  3. #13
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    Default Re: telnet connection delay

    Quote Originally Posted by tsu2 View Post
    Ok,
    a reverse lookup wouldn't happen for an attempted telnet connection, reverse lookups are useful only for more complex analytical applications, not simple network connections.
    I agree with that, but the OP has the idea that the delay is due to a reverse lookup. Thus, instead of telling him that there is no reverse lookup for a telnet by IP address (which he may believe or not), I offered him a way to test himself with a clean reverse lookup, the result of which, his own test, he most probably will believe.

    BTW, I use telnet also only as you described above. But the OP has this problem, thus I try to help him. In the mean time hinting him (by telling I only use SSH) that there may be a better way then using telnet. But again, that is not his problem.
    Last edited by hcvv; 15-Jul-2019 at 11:19.
    Henk van Velden

  4. #14
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    Default Re: telnet connection delay

    Telnet 192.168.0.1 is how I used to connect to my old routers, before the current and previous. Is 192.168.1.1 your router? Telnet is how I connect to my two STBs with 15.1. I get no delay anywhere.
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  5. #15

    Default Re: telnet connection delay

    admin@linux-tlpp:~> telnet
    The delay arises already at this stage.
    telnet>

    I noticed that if use sudo, there is no delay


    admin@linux-tlpp:~> strace -i -T -r telnet 192.168.1.1
    without sudo
    0.000081 [00007fb034987164] poll([{fd=3, events=POLLIN|POLLERR|POLLHUP}], 1, 5000

    with sudo
    0.000081 [00007fb034987164] poll([{fd=3, events=POLLIN|POLLE 0.000000 [00007fee490d1517] execve("/usr/bin/telnet", ["telnet", "192.168.1.1"], 0x7ffc742beac0 /* 15 vars */) = 0 <0.000124>

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