oof, the situation can be even rougher than that. At 9000 MTU on IPv4, you have a 'safe' NFS-over-UDP data rate of roughly 18 megabytes/second. Plenty of room at 1GbE, but not enough for 10GbE or greater. I suppose using krb5i/p mounts or some other integrity-providing GSSAPI/crypto implementation could help with this, but thats a different pile of worms. You would also get issues with not-strictly-necessary retransmits impacting your effective bandwidth.

Thankfully, IPV6 can help mitigate this problem by extending the fragment id length from 16 to 32 bits. This gets you up to roughly 1.18 trillion bytes of 'safe' NFS traffic/second. There's plenty of reasons why IPv6 adoption is still fragmentary, but if you're running a high throughput network, this is certainly a motivator to move at least part of it to IPv6.