Arcetri Astrophysical Observatory

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Connectivity problems self help

L. Fini. Novembre 2012
 

In this document there is a collection of different suggestions useful to identify and solve problems of connectivity to the Arcetri LAN. We suggest to do the suggested tests before asking for support: your problem might be easy and fast to solve and in any case you will have some specific information to pass to the support people when you call for help.

The computer doesn't "see" the network

The reasons might be many:

  1. Physical access to the LAN. The best test is to use the ping command:
    • Open an interactive window. The necessary application is usually identified by icons of this kind:

      Normally they are in the Accessories menu (Windows), in the System menu (Linux) or amongst the application icons (Mac).
       
    • Type one of the following commands:

      ping 193.206.154.1
      ping 193.206.154.33
      ping 193.206.154.170
       
    • If the command doesn't end by itself, stop it with Control-C
       
    • The command output must be a few lines (one per second) that will show you if the network device is answering. Examples:

      64 bytes from 193.206.154.1: icmp_req=1 ttl=64 time=0.552 ms
      Reply from 193.206.154.1: bytes=32 time<1ms TTL=127

      If it doesn't answer you will see something like:

      Request timed out
      From 193.206.154.1 icmp_seq=3 Destination Host Unreachable

      or nothing and you will have to hit Control-C after a while to get back to the prompt.
       
    • If the ping commands give the right answer then you are connected to the LAN and you can move to the next test. Otherwise please go here.

      Note: If some of these commands give the right answer and some other no, it is not a problem of your connection but a problem of the network device you are probing. In this case please call one of the IT service staff people to notify the problem as soon as possible. 

  2. DNS problems. Use the ping as before.
     
    • Type one of the following commands:

      ping arcrt1.arcetri.astro.it
      ping hercules.arcetri.astro.it
      ping ebe.arcetri.astro.it
       
    • If you will get the reply lines as before your DNS setup is OK .
    • If you don't get a reply answer please check the first output line. It will be like:

      PING arcrt1.arcetri.astro.it (193.206.154.1) 56(84) bytes of data.
      Pinging arcrt1.arcetri.astro.it [193.206.154.1] with 32 bytes of data:

      Please check if the IP number inside the braces matches the name. The names arcrt1, hercules, ebe correspond, in this order, to the three numbers listed before for the first test with the ping command.

      If the number matches the name, DNS is working even if you didn't get a reply answer. If it doesn't match or if the command output is: unknown host xxx.arcetri.astro.it, then your DNS configuration is wrong or there is a problem with the DNS server: please contact support staff for assistance.

  3. WAN access. If you are at this point you are correctly connected to the LAN. If you are still unable to use some of the internal services (Web pages, e-mail or something else) the problem is of the related server or in the configuration of your client application (browser, e-mail reader etc.) or you did something wrong.

    If you cannot access an external service (i.e. a web page) please try with other services in order to verify if the problem is in that specific remote server. We suggest to test, with the browser, one of the following URLs or others that you might prefer. www.garr.it is the site of our network provider, if it is unreachable most probably there is a problem of connectivity from Arcetri to the internet. In this case please notify the support staff as soon as possible.

    http://www.garr.it
    http://www.inaf.it
    http://www.eso.org
    http://www.repubblica.it

    If some of this sites are reachable and other no, the problem is of the faulty sites. Please try again later.

    If no one is reachable, then there is a problem of connectivity from Arcetri to the internet. Please notify the support staff as soon as possible.

 Fixing physical connection problems 

There are a few causes:

  1. If you are using a desktop computer with a permanent IP number and you are connected to the LAN with a cable (which is the rule for desktop computers), please check the ethernet cable.
    • The cable is connected to the back of your computer and looks like this:

      The cable should connect your computer to a socket in the wall, or to a small device (switch) which should be connected to the wall socket.

    • If there are free sockets in the small wall box, please try to use one of them.

    • If near to you there is another computer with the same connection, try to unplug it from the socket it's using and to connect it in the same socket previously used by the computer that doesn't work (ask before the user of the other PC for permission!). Don't try to connect the two computers together with a cable: it will not work.

    • Some computer network cards have a small LED which is on when a network link is established. It is a useful check to do to understand if the problem is a hardware or software problem.

    • If you are connected through a switch and there is another device connected to the same switch (computer, printer or something else) please check if the other device is connected. If it doesn't work it is probably a switch problem or a problem of the connection between the switch and the LAN (cable, socket etc. as before).

    • If you are connected through a switch please try to bypass it, that is to connect the computer directly to the wall socket instead of to the switch. If in this way the computer is connected again the switch is broken.

    • A simple ping command as described before is enough to test the computer connectivity to the LAN.

    If everything fails call the support staff. 

  2. If you are using a laptop or other mobile devices, the first thing to do is to check if your MAC address is correctly registered. You can go to this page (from another computer) at this web page and use the "Check your MAC address" section. If you don't find it you should register to be authorized and receive a temporary IP number form the LAN DHCP server.

    Note: The cable transceiver and the wi-fi tranceiver have different Mac addresses! Please verify that you entered the right one.

    As explained in the first paragraph, use the ping command:

    ping 192.168.128.1

    If the answer is positive but the other tests of the first paragraph are neagative, there is a problem in the gateway computer (named "polifemo") which translates the DHCP subnet addresses to the LAN. Please call the support team.

    The next test depends on the connection mode.

    • Your laptop is connected with a network cable. Test the connection as explained for desktop computers.

    • Your laptop is connected by wi-fi. Check if the wi-fi signal is visible in the dedicated panel or icon. If it is not visible you might be too far from the closest wi-fi transceiver, or the transceiver itself might be broken. Please ask to people near to you if they have wi-fi problems.

    • If the signal is visible try to switch off and on again your laptop wi-fi transceiver.

    • If the wi-fi connection icon says that you are connected but the network doesn't work please repeat the test with the ping command as described above.

    • If you still cannot use the network, try to use a cable instead of the wi-fi. If it works you have not tracked down the problem but you can work...

    • When everything seems faulty and nothing helps call the support team!