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Thread: telnet connection delay

  1. #1

    Default telnet connection delay

    Hello!


    When trying to connect with something after


    admin@linux-tlpp:~> telnet 192.168.1.1

    <--- here for some reason there is a delay

    Trying 192.168.1.1...
    Connected to 192.168.1.1.
    username:



    admin@linux-tlpp:~> cat /proc/version
    Linux version 4.12.14-lp151.28.7-default gcc version 7.4.0 (SUSE Linux)

    admin@linux-tlpp:~> time telnet 127.0.0.1
    Trying 127.0.0.1...
    telnet: connect to address 127.0.0.1: Connection refused
    real 0m5,068s
    user 0m0,002s
    sys 0m0,000s

    admin@linux-tlpp:~> cat /etc/nsswitch.conf
    passwd: compat
    group: compat
    shadow: compat
    hosts: dns files
    networks: files dns
    services: files
    protocols: files
    rpc: files
    ethers: files
    netmasks: files
    netgroup: files nis
    publickey: files
    bootparams: files
    automount: files nis
    aliases: files


    admin@linux-tlpp:~> cat /etc/resolv.conf
    nameserver 10.10.0.111
    nameserver 10.10.2.20
    nameserver 8.8.8.8

  2. #2
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    Default Re: telnet connection delay

    I can only speculate here, but any delay with authenticating will be down to the server you're connecting to, so that's probably where you should focus your attention. This could be a security mechanism to limit brute force attack attempts for example.
    openSUSE Leap 15.0; KDE Plasma 5

  3. #3
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    Default Re: telnet connection delay

    I have no idea why you have that delay, but I get the impression you are looking in the wrong direction. As you use IP addresses and not host names, DNS has no role here and thus neither /etc/resolv.conf, nor /etc/nsswitch.conf are of importance.

    As I have no telnet deamons running (SSH only), I can not try to re-create your problem here to a listening deamon. But
    Code:
    henk@boven:~> telnet 10.0.0.138
    Trying 10.0.0.138...
    telnet: connect to address 10.0.0.138: Connection refused
    henk@boven:~> telnet 10.0.0.44
    Trying 10.0.0.44...
    telnet: connect to address 10.0.0.44: No route to host
    henk@boven:~>
    The first system exists, runs, but has no listening telnet port and has no delay at all
    The second system does not exist at all and has a delay (time out) after Trying ...., which looks logical to me.
    Henk van Velden

  4. #4

    Default Re: telnet connection delay

    Quote Originally Posted by deano_ferrari View Post
    I can only speculate here, but any delay with authenticating will be down to the server you're connecting to, so that's probably where you should focus your attention. This could be a security mechanism to limit brute force attack attempts for example.

    The problem is on my PC. From other hosts, everything is fine. I am inclined to think that the matter is in reverse resolv.

  5. #5

    Default Re: telnet connection delay

    Quote Originally Posted by hcvv View Post
    I have no idea why you have that delay, but I get the impression you are looking in the wrong direction. As you use IP addresses and not host names, DNS has no role here and thus neither /etc/resolv.conf, nor /etc/nsswitch.conf are of importance.

    As I have no telnet deamons running (SSH only), I can not try to re-create your problem here to a listening deamon. But
    Code:
    henk@boven:~> telnet 10.0.0.138
    Trying 10.0.0.138...
    telnet: connect to address 10.0.0.138: Connection refused
    henk@boven:~> telnet 10.0.0.44
    Trying 10.0.0.44...
    telnet: connect to address 10.0.0.44: No route to host
    henk@boven:~>
    The first system exists, runs, but has no listening telnet port and has no delay at all
    The second system does not exist at all and has a delay (time out) after Trying ...., which looks logical to me.
    An interesting note. It's worth thinking about. Yes, pause exactly before Trying

  6. #6
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    Default Re: telnet connection delay

    Quote Originally Posted by gorn View Post
    I am inclined to think that the matter is in reverse resolv.
    And what if you do a reversed reolve yourself?
    Code:
    nslookup 192.168.1.1
    or
    Code:
    host 192.168.1.1
    Henk van Velden

  7. #7

    Default Re: telnet connection delay

    Quote Originally Posted by hcvv View Post
    And what if you do a reversed reolve yourself?
    Code:
    nslookup 192.168.1.1
    or
    Code:
    host 192.168.1.1

    admin@linux-tlpp:~> host 192.168.1.1

    Host 1.1.168.192.in-addr.arpa. not found: 3(NXDOMAIN)

  8. #8
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    Default Re: telnet connection delay

    Quote Originally Posted by gorn View Post

    admin@linux-tlpp:~> host 192.168.1.1

    Host 1.1.168.192.in-addr.arpa. not found: 3(NXDOMAIN)
    (Please CODE tags)
    I can understand the result, but I can not see if there was a delay. And that is where the test should be done for.
    Henk van Velden

  9. #9
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    Default Re: telnet connection delay

    Aside from your problem,

    I caution you to never run a telnet server.
    Telnet sessions send your credentials and session content in clear text.
    Use ssh instead.

    I use the telnet client only in my troubleshooting toolbox to probe ports on remote machines, nothing more.

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  10. #10
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    Default Re: telnet connection delay

    Quote Originally Posted by gorn View Post

    admin@linux-tlpp:~> host 192.168.1.1

    Host 1.1.168.192.in-addr.arpa. not found: 3(NXDOMAIN)
    That means your machine sent a hostname query to your DNS,
    And your DNS doesn't have a reverse lookup zone configured.

    That's curious that your machine might read an IP address as a hostname and not as an IP address...
    Are you sure your machine is set up for same network (and netmask) so that if the remote address isn't on your network that your machine knows to use your DG?
    eg
    If your machine has an address 192.168.2.1/16
    and the machine with address 192.168.1.1 is on another physical network.

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