Are there network switches under your control? It sounds similar to what happens when MTU on the systems MTU do not match or one system MTU is set above the value on the switch ports.

Next time the issue occurs use ping with the do not fragment flag.
ex $ ping -m DO -s 8972 ip.address

This example should be the highest value to work in the case of MTU size 9000, there is 28 byte overhead for IPv4 packets.

Second, are you sure no one is attaching to the network and duplicating the MAC address of your NFS server or perhaps the system that is stalled? If the switches are manageable you would have to insure that the MAC addresses are being learned on the correct ports.

-Jamie


On Sun, Sep 26, 2021 at 10:24 AM Tom Horsley <horsley1953@gmail.com> wrote:
On Sun, 26 Sep 2021 10:26:19 -0300
George N. White III wrote:

> If you have cron jobs that use a lot of network bandwidth it may work
> fine until some network issue causing lots of retransmits bogs it down.

Which is why you should check the dumb stuff first! Has a critter
chewed on the ethernet cable to the server?
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