Some PCI motherboards contain DMA chipsets that are unable to support 100-Mbps Fast Ethernet. The Solaris environment does not support 100-Mbps PCI network operation on systems containing the slow chipsets. This problem affects PCI cards only.
These chipsets are known to exhibit this problem:
82450GX (Orion) (A and B steppings only)
These chipsets do not exhibit this problem:
82430HX (Triton II)
82450GX (Orion) (C0 stepping and later)
In particular, PCI cards supported by the dnet and iprb drivers don't perform well on machines with the problem chipsets. You must decide whether the performance on a particular machine is adequate for the intended purpose.