Switch stop connectivity - bad line

Posted on 2008-11-06
Last Modified: 2013-11-05
The whole network stop responding and connectivity stops between devices and to the server. when I disconnect -the cables manual- from some links then I got the I get connectivity back. when I put those cables back it disconnect.

what is the problem?  I haven't search where are those lines going -computers, printers ..etc.
any thoughts. thanks
Question by:fm250
    LVL 11

    Assisted Solution

    Is it possible that those line are to another switch/router?  If so it could be Spanning Tree Protocol blocking the ports.  
    Is the server multi-homed and acting as a router?
    LVL 10

    Author Comment

    Yes the lines are to a switch, but if I disconnect some lines from that other switch it works. What is the sapnning tree problem, it is unmanaged switch.
    LVL 23

    Accepted Solution

    Having spanning tree support is independent from being managed or not;
    there are some unmanaged switches that have been marketed that support
    spanning tree   (STP cannot be turned off).

    But indeed; most likely your unmanaged switches have no support.

    What  may be happening is  a loop has formed on your network, causing a broadcast storm.   You could also have an errant PC  (perhaps with a bad network card or bad cable between PC/switch or between switch/switch),
    or a workstation running a virus that is flooding your LAN with traffic.

    Regarding broadcast storms that a loop can cause... it is ok to connect two switches together.   But check to make sure you don't have any switches accidentally plugged into themself,  or plugged into the LAN twice somehow  (you can only plug a switch in multiple times if all switches in the cycle fully support and have spanning tree protocol fully enabled).

    Sometimes users might plug their network drop into a VoIP phone, plug a 5-port switch into the PC port of their phone,  plug the switch at their desk into a second network drop  (creating just such a loop and taking down the whole LAN).

    When loss of connectivity occurs, can you ping between two devices, i.e. is it just the server becomes unavailable to all PCs?

    If just the server becomes unavailable, then it may be that another PC on the network configured with an IP address that conflicts with the server's IP
    (i.e. a workstation statically set to attempt to use the same IP)

    There are some other possible causes of broadcast storms.

    I recommend downloading and installing the free tool called "Wireshark"   on a management PC

    And running a brief capture session while connectivity is disrupted.

    So you can get an idea of the type of traffic,  if there _is_ a broadcast storm.

    LVL 10

    Assisted Solution

    Your switch dont have STP.

    Check if you connect a 2nd switch twice on on you central! This will create a loop and a broadcast storm. Also, check if you have a cable accidentally connected twice on the same switch, creating a loop
    LVL 10

    Author Comment

    It seems it is a bad old cable or print server connecting to that switch. Now I have one managed main switch let's say s1 and a connection from it to the second trouble switch let's say s2 which is unmanaged.   Can I enable the STP on s1 and the problem will not circulate to the devices on s1?
     the managed switch is: linksys SRW224G4.

    Featured Post

    Top 6 Sources for Identifying Threat Actor TTPs

    Understanding your enemy is essential. These six sources will help you identify the most popular threat actor tactics, techniques, and procedures (TTPs).

    Join & Write a Comment

    Join Greg Farro and Ethan Banks from Packet Pushers ( and Greg Ross from Paessler ( for a discussion about smart network …
    Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
    Here's a very brief overview of the methods PRTG Network Monitor ( offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

    729 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    19 Experts available now in Live!

    Get 1:1 Help Now