RH ES4: SCTP kernel module not automatically loaded

I am running RH ES4, kernel 2.6.9-67, sctp is configured as a loadable 
module.

When I try to create a SCTP socket:
int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP);

I get the error that the socket type is not supported and the sctp module 
doesn't get loaded.

If I load first manually the module like that:
insmod /lib/modules/2.6.9-67.EL/kernel/net/sctp.ko

I can then successfully create the SCTP socket.

Why does the kernel not automatically load the sctp module when required?

Thank you.