network blips every couple minutes

Posted on 2016-09-06
Last Modified: 2016-09-14
We have a bunch of 24 port switches - each plugged into a port on our firewall with it's own subnet.

All of the clients attached to a particular one of the switches would lose most connectivity every couple minutes for a minute or so.

so for instance would be pinging (it's own gateway) (gateway of servers IP) (main server)

1.1 and 1.7 would fail, but somehow 31.1 would still reply.... BUT firewall company says the packet never got to them because sniffer saw nothing come in during that time.....

Anyway - so we rebooted switch - issue persisted - so we moved all the cables from that switch to another switch on another subnet... things are working fine so far...

strange thing is we can plug in a laptop to the original "Bad" switch and now pings run fine on it....

Totally confused - any idea what the issue could have been?
Question by:Xetroximyn
  • 3
  • 2
LVL 37

Accepted Solution

ArneLovius earned 500 total points
ID: 41786842
excepting changes to the local routing table, if the gateway address is on the firewall, and pings to the gateway were okay and pings to addresses beyond the gateway were not, then the problem is not the local switch but either the firewall or beyond the firewall.

Author Comment

ID: 41787105
firewall tech was doing a sniffer - claims that nothing was coming into firewall while at same time my guy onsite says he was getting replies.... I wonder if something could have somehow been static set to same ip as gateway and fighting it?  

Anyway, Things are still all good as it stands.... just so weird.... wonder if it could have been overheating?  Traffic flows, causes heat, causes problems, traffic stops, it cools down, traffic flows again.  But that doesnt explain how we got ping replies from 30.1 when fortigate sniffer saw no such traffic.
LVL 37

Assisted Solution

ArneLovius earned 500 total points
ID: 41787519
it would be "unusual" for a L2 switch to overheat because of traffic flow...

something else taking the default gateway address could cause the problem you saw, the way to check if it happens again is to check the ARP cache with "arp -a" and see if the MAC address matches the expected MAC address

Author Comment

ID: 41788206
Thanks - should have checked arp when we were troubleshooting!!   Oh well - it's working now, so I am leaving it.

Question... would the fact it's a server room with not great airflow, a completely mess of cables, and is about 76 degrees because the A/C unit is not quite as powerful as it should be change your mind at all about the overheating probability?   (Also the switch is probably 10 years old.... and likely never air dusted.... so dust may have collected in decent quantities by now.)
LVL 37

Assisted Solution

ArneLovius earned 500 total points
ID: 41789460
heat "may" be an issue, do the switches have a management interface ?

if the switches are ten years old, any initial warranty is long gone, so you could open them and give them a blast from a can of compressed air.

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

In the hope of saving someone else's sanity... About a year ago we bought a Cisco 1921 router with two ADSL/VDSL EHWIC cards to load balance local network traffic over the two broadband lines we have, but we couldn't get the routing to work consi…
If your business is like most, chances are you still need to maintain a fax infrastructure for your staff. It’s hard to believe that a communication technology that was thriving in the mid-80s could still be an essential part of your team’s modern I…
Viewers will learn how to connect to a wireless network using the network security key. They will also learn how to access the IP address and DNS server for connections that must be done manually. After setting up a router, find the network security…
In this tutorial you'll learn about bandwidth monitoring with flows and packet sniffing with our network monitoring solution PRTG Network Monitor ( If you're interested in additional methods for monitoring bandwidt…

821 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