forcing speed/mode on a NIC

I have Red Hat 8.0. I want to force the NIC to 100 Full Duplex. I’m assuming that the default is auto negotiate. I manage many Solaris servers and found that the negotiation isn’t always working with our switches so all ports are forced 100 FD onthe switches. I could set a port back to Auto but I’d rather not. In Solaris ndd is used to set this and many other parameters. I have found that the other similiar parameters are set via /etc/sysctl.conf in Linux, but I don’t see the proper syntax for doing this one anywhere.