switches cause erratic PING reply

We have a router supplied by an external co. with 2 IP ranges on it. The main network of 4 or so switches is connected to each router ports via cat5 from switch1.

Have setup a computer with static IP in range to test.

Plug the computer directly into the router with a crossover cable and it replies to PING all day from both ports.

Plug the computer directly into ANY of the 4 switches with a cat5 cable, and one range replies to PING fine, the other range replies erratically, often ‘request timed out’ (changing IP of computer before of course).
My switches are obviously the culprit, they are all Dlink GB 1224T which have a management IP of 192.x.x.x. They have spanning tree protocol setup on them. There’s no firewall onsite.
What would cause this erratic reply behaviour?
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Don JohnstonInstructorCommented:
Duplex mismatch. Check that the switchport and the PC are both set to full duplex.

Are there new switches or used switches? Are they managed switches? If they are managed to they have any configuration in them? VLANs? Port Channels? If they're used have you successfully used them in another situation?Are they a layer 3 switch?
PeteAuthor Commented:
duplex is set to auto\full on everything.
they have been stable using range 1 for a couple of years, range 2 is new (but it works from crossover test directly into router so the router is presumably setup correctly).
They are managed with just spanning tree enabled
They are layer 2
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Here is my thought. If your host connected to the switch and ping your router fine on the first range of addresses it's not the switch. Think about how the switch works. It takes only layer two information and forwards it to the device with the destination mac address. I hear you you're saying with the crossover test too, and to that I can't answer right now. For me my first stop would be the router. Check and double check it's configured correctly. Don't completely rule out the switch, but if you can ping the first port fine and the  second every so often I'd start at the router then work my way down..Try and ping both hosts from the router.

I say "seems like" because I am still thinking through why you get replies consistently with the crossover cable (Hence why I asked if it's a layer 3 switch. To see if perhaps it was trying to do some sort of routing)
PeteAuthor Commented:
the 3rd party who supply\support the router looked at 2 tests:
  • They ping to a workstation connected inside the school (through the switches)
  • We ping them using corssover cable direct into router
both tests pinged continually, so they now will not support us any further in this issue as it's a local problem (according to them)....
So they ping both hosts from the router and it responded continually? Then you ping from one host to a host on a different subnet and it fails? That's interesting. What are the two subnets for each of the routers interfaces?
PeteAuthor Commented:
I never know whether it is 'safe' to advsertise my IP ranges\details on public forums...?
Are they public ranges? If so, then yes. Don't advertise them. If they're private ranges, you're good.
PeteAuthor Commented:
they are both 10.x.x.x
does that make them private?
Yes the private ranges are: - - -
PeteAuthor Commented:

Range 1:

Range 2:
Hi, to find out if the problem is in your switches you need to look at your ARP settings.
1. On the COmputer, command prompt type in ipconfig/all
    i. Get the MAc (Physical) address of your NIC, i.e. 00-22-69-06-B9-E8
   ii. Type in ARP -a You will see your arp table. Make note of the Routes IP Address and MAC address and broadcast address. hint, if this table is empty go a quick ping of the network, i.e. ping then check the arp table again.
2. On the router, if a Cisco in enable mode, type in sh arp You will get the arp table of the router, note the PC, Switch's IP address and MAC address.
3. Log onto your switch and go to the ARP table, check the enteries. MAke sure the MAC addresses and IP Addresses coresponde to the correct switch ports that the devices are connected to.
   i. Another critical entery to look at is the time the arp entry will stay active before it expires, similar to a DHCP address lease.

This will help elimate any arp table issues. I've had similar problems where the arp entry is set to 5 hours and when you move the PC to a different port it keeps sending the packets to the previous port. Hint, the switches IP address is only a management address, in that it is not used by the network, only to connect to it and manager it.

If you require further explanation, post the arp enteries and the device ip addresses and a network connectivity sketch

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PeteAuthor Commented:
I am unable to access the router as it's managed by 3rd party. i will contact them.
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