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Sudden loss of ping

Posted on 2014-02-06
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Last Modified: 2014-02-10
We have a mature network, and fairly plain vanilla.  200 Pcs, 15 servers.

I'm the sys admin.


I've found 5 static IPs I cannot ping from my PC; everything else I can ping. I don't recall this problem before. (My PC has a dynamically assigned IP)

I rdp into a server; that server can ping these  5 IPs (and anything else I try)



Where do I start looking to solve such an odd problem?




I have Win 7, we have Win 2003 and Win 2008 servers.

All machines mentioned are on 192.168.150.nnn

Static IPs are 150.55 and down. DHCP scope is 150.56 and up (into 151.200)


(Possibly red herring; we have a current problem with a switch, causing BAD_ADDRESS lines to fill up the DHCP scope. Sometimes we delete them if a user can't get on, and they then get on. Doesn't seem to affect loged-on users. We're working on it. I'm confident my non-ping problem pre-dates this.)

Thanks

Larry
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Question by:cgunix
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by:John Hurst
John Hurst earned 250 total points
ID: 39840578
I would do several simple things to get started.

1. Replace any problem switch. A problem switch is not worth the aggravation. I do such a thing routinely.

2. For any other switch or router in the network, upgrade firmware if you can.

3. Restart all the switches. That is, restart your network. Off hours of course.

4. Restart servers on a one-by-one basis with problem servers at the start.

Then if problems persist, let's troubleshoot.

.... Thinkpads_User
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IT_admin_031 earned 250 total points
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Larry,

I think the first thing I would do is trace the cable(s) from the server. Find out what they are plugged into and document this for future troubleshooting.

If you can ping something from a server but not the desktop, you may have a bad switch somewhere or you have a multi-homed server that connects to a switch that is not connected to the regular network.

It may be done on purpose as to keep some traffic of the main LAN. A VLAN or routed traffic may be why you can't ping it.

If all 5 are on a switch that does not allow ICMP it will just not reply, but if you telnet to the IP and get a connection refused, this would be clue to one of the 2 scenarios above.  
 

In DHCP, reduce your lease time from default to a few days. Mine is set to 8 hours. a BAD_ADDRESS can mean the device is not on, but is holding the lease. At least this is what I believe is happening. I had a similar problem, lowered the lease time and the problem went away. When you get those, right click your scope and choose "Display Statisics..." This will show you how many are in use. From that same menu, you can choose "Reconcile" This will free up addresses if this is the case. If you have wireless bridged into your regular scope, you may want to split this into another scope, or create a super scope.
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Author Closing Comment

by:cgunix
ID: 39848572
Interesting problem - here's what happened.

A while ago we were running close on IPs for DHCP to hand out. We'd been using ...150.nnn and we added ...151.nnn. To accomplish this we changed the subnet mask from 255 in the third octet to 254. DHCP passed this new subnet out.

Most often my PC would happen to get an IP in the 150.nnn range - things worked fine.

My ping problem occurred when the DHCP flooding caused me to get an IP in the 151.nnn - range. I was still generally OK as far as general work went.

The ping problem occurred when I tried to connect to machines that were statically assigned an IP __** AND **__  whose subnet mask I had neglected to change. Those machines didn't know how to get back to me with the ping results.

As soon as I went into a machine and corrected the subnet mask, ping worked.

Thanks for you help. I appreciate this forum.
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by:John Hurst
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@cgunix - Thanks for the update and I was happy to help.
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