Eleven layer2 managed NetGear switches. Have a strange problem in that some default OS install PCs are unpingable ( newDefaultInstall ) from host X until host X is pinged by the new machine. All newDefaultInstall hosts have firewall disabled with ACCEPT as default. What are the typical places to look to solve this type of problem? It is something with the switches, not the hosts because when i hook both machines upto a new dummy switch, works as expected.. Can an electrical surge do this because this problem happened out of the blue?

    HostX> ping -s 40999 newDefaultInstall
    Request timed out.
    Request timed out.
    Request timed out.
    Request timed out.

<... Continues to time out until opposite ping is run ...>

    41007 bytes from newDefaultInstall ( icmp_seq=4 ttl=64 time=1.25 ms
41007 bytes from newDefaultInstall ( icmp_seq=5 ttl=64 time=1.06 ms
41007 bytes from newDefaultInstall ( icmp_seq=6 ttl=64 time=0.998 ms
41007 bytes from newDefaultInstall ( icmp_seq=7 ttl=64 time=1.23 ms

Once the following oppisite ping is entered, both pings work immediately.

newDefaultInstall> ping -s 40999 HostX
41007 bytes from HostX
41007 bytes from HostX
41007 bytes from HostX
  • 1
    Just from a basics perspective, to me it sounds like the switches don't have a mac address until the new machine specifically puts traffic on the network. It's not discovering the host until then. Are the new machines not receiving ARP broadcasts or something? (probably will need a sanitized switch config, if I know this stack)
    – Radhil
    Dec 5, 2018 at 23:21
  • 1
    If you send one packet to "enable" the pings, do they fail again after an amount of time, perhaps 90s or so? Are you able to run a wireshark or similar? It looks like potentially mismatched masks. It works because the incoming ping puts and entry in the ARP cache.
    – jonathanjo
    Dec 5, 2018 at 23:44
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    – Ron Maupin
    Dec 25, 2018 at 10:10

1 Answer 1


While the issue is occuring - does HostX have an ARP entry for newDefaultInstall? Assuming these are Windows machines, use arp -a on HostX to get a list - you should see a MAC address for the newDefaultInstall IP. Compare that ARP entry to the MAC address of newDefaultInstall (found using ipconfig /all) and make sure they match. If they do not, then you may have a duplicate IP address on the network. If there is no entry, check the ARP table on the newDefaultInstall and look for an entry for 'HostX' - compare against ipconfig /all again to make sure they match.

If there are no MAC addresses being learnt (or only in one direction), check the subnet mask that is configured on newDefaultInstall and HostX - it may be that one host has a longer mask and is unable to send ARP for the other without trying it's default gateway first.

Check that there is only a single network connection on each node - is there both a wired and wireless connection on the same subnet that may responding asymmetrically - if so, disable the wireless adapter and see if that changes things.

Depending on the capabilities of your Netgear switches, check the forwarding table of each and confirm that both device MACs are learnt end-to-end on the correct switch ports.

Confirm that each of your Netgear switches do not have any port security functionality (DHCP-Snooping, Dynamic ARP Inspection, MAC limiting etc.) enabled, and if they do, disable these features during your testing.

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