Solaris 10 NFS not responding still trying when setting ixgbe.conf mtu size higher then 1500 connect

Solaris 10 u11sparc,  NFS not responding still trying when setting ixgbe.conf mtu size higher then 1500 connecting to ZFS appliance 7420

when I set mtu to 1500 its ok.

Jun  8 11:26:58 sy-pinow nfs: NFS server sw-7420b10g ok

Jun  8 11:27:05 sy-pinow last message repeated 1 time

Jun  8 11:27:08 sy-pinow nfs: NFS server sw-7420b10g not responding still trying

Jun  8 11:31:00 sy-pinow nfs: NFS server sw-7420b10g ok

Jun  8 11:33:08 sy-pinow nfs: NFS server sw-7420b10g not responding still trying

Heres the ixgbe.conf

name = "pciex8086,10fb" parent = "/pci@400/pci@2/pci@0/pci@0" unit-address = "0" default_mtu = 9000;

#lso_enable=0;

flow_control = 3;

rx_ring_size = 3072;

tx_ring_size = 3072;