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Wired Networks Thread, Something is blocking traffic somewhere? in Technical; Bit of a random issue happening to random servers and I would appreciate any ideas/suggestions? Our 2nd Domain Controller is ...
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    Nick_Parker's Avatar
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    Something is blocking traffic somewhere?

    Bit of a random issue happening to random servers and I would appreciate any ideas/suggestions?

    Our 2nd Domain Controller is 192.168.0.2.
    This morning I couldn't ping or remote into it from my laptop (I can connect to and ping everything else) but I could from another PC.
    The server in question currently has the firewall disabled while I try and resolve this so it isn't that causing it.
    Suddenly I can ping it again and remote desktop but it looks like nothing has changed?

    Now it's happening to another server, 192.168.0.105.
    I can't ping or remote desktop into it but I can from another machine. Once again, no firewall.

    It's not just me tho, I have another PC in our office that sits and pings servers and puts the results up on a screen, it currently cannot ping 192.168.0.2 and it showing it as offline but I can ping and remote desktop into 192.168.0.2.

    It's obviously not the firewall causing it so the only other thing I can think of is that it's a switch somewhere, is this something a switch can do? Some sort of flood control? Or am I missing something?

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    Can you ping it from other machines outside of the 192.168.0.0 network? Are you getting timeouts or unreachables?

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    Nick_Parker's Avatar
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    Hey @Homer,

    I'm getting a mix of both Request timed out and Destination host unreachable.

    This morning I cannot ping 192.168.2.70 (a printer).
    My IP is 192.168.11.223.
    I can ping it from another machine in my office 192.168.6.180.
    All of the devices/pcs are on the same subnet 255.255.224.0

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    Possibly a switch failure, unlikely to be cabling as their is more than one device affected, although testing them on other access points would show if cabling was at fault.

    Do you have a back up switch you could swap in place to see if it it is at fault.?

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    Nick_Parker's Avatar
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    I'm beginning to think it may be a faulty switch somewhere, somebody else mentioned corrupt routing tables.
    Either way, there are over 26 switches throughout the campus, I'm gonna have to start narrowing it down switch by switch

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    Nick_Parker's Avatar
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    So I haven't had much luck finding the fault yet but today something very weird happened.

    Somebody asked me if I could ping 192.168.0.2 so I opened up command prompt and tried to ping it.
    One packet went through straight away and then nothing after that.

    Ping.png

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    Nick_Parker's Avatar
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    Weird thing #2:
    I haven't been able to ping 192.168.0.105 all morning.
    I just went into the server room to reboot it and suddenly my ping requests changed from "Request timed out." to "Destination host unreachable."
    As soon as the server had finished rebooting I still couldn't ping it but the ping requests changed back to "Request timed out."

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    Have you checked the server itself to see whether it has a network connection? Try pings, trace route, nslookups, etc. check the default gateway on the server as well.

    Have you tried rebooting the server?

    Is there any shared hardware or a switch with the two servers?

    Have you looked at the traffic on the switch or switches they are connected to and your core switch?

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    Nick_Parker's Avatar
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    Quote Originally Posted by seawolf View Post
    Have you checked the server itself to see whether it has a network connection? Try pings, trace route, nslookups, etc. check the default gateway on the server as well.

    Have you tried rebooting the server?

    Is there any shared hardware or a switch with the two servers?

    Have you looked at the traffic on the switch or switches they are connected to and your core switch?
    The Server is definitely up and running, some machines can ping it, some can't.
    Rebooting didn't do anything.
    All the servers in the server room are connected to one switch so that could be a potential point of failure.
    I'm trying to figure out how to do the traffic tracing etc on the switch but no luck yet.

    Something weird happened this morning.
    I couldn't ping 192.168.0.2 from my machine (192.168.11.223)
    I remote desktop into the server running the virtualized domain server (192.168.0.106) and open up the Hyper-V'd domain server.
    I try and ping my machine from 192.168.0.2 and the packets go through, the second the first packet is delivered from 192.168.0.2 to 192.168.11.223, my machine (192.168.11.223) starts successfully pinging 192.168.0.2.

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    Quote Originally Posted by Nick_Parker View Post
    The Server is definitely up and running, some machines can ping it, some can't.
    Rebooting didn't do anything.
    All the servers in the server room are connected to one switch so that could be a potential point of failure.
    I'm trying to figure out how to do the traffic tracing etc on the switch but no luck yet.

    Something weird happened this morning.
    I couldn't ping 192.168.0.2 from my machine (192.168.11.223)
    I remote desktop into the server running the virtualized domain server (192.168.0.106) and open up the Hyper-V'd domain server.
    I try and ping my machine from 192.168.0.2 and the packets go through, the second the first packet is delivered from 192.168.0.2 to 192.168.11.223, my machine (192.168.11.223) starts successfully pinging 192.168.0.2.
    Do you have a network diagram showing how your servers are connected and what is virtual vs. physical. This could simply be a problem with a vSwitch, but it's difficult to say without more info.

    What make and model of switches are the servers connected to? Do you have a network monitor of any kind? If not download "The Dude" and run it to recon your network, or install Spiceworks and have it trawl the network for a while. A network monitor of any sort would help you isolate this problem a lot better.

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