Due to a problem with the simulation model of the Intel® FPGA Triple-Speed Ethernet IP core, both rx_clk and tx_clk output of the Intel® FPGA Triple-Speed Ethernet IP core stop after about 1.7 sec in the simulation.
This is due to the MSB of the internal 32-bits clock counter not toggled.
This problem can be seen in only simulation.
There is no workaround for this problem.
This problem is fixed starting with the Intel® Quartus® Prime Standard Edition software version 21.1.