FreeBsd as internet router

[Ong Beng Hui]

Hi,

Looking thru the FreeBSD handbook...

http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/index.html

and Advanced Networking...

http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/advanced-networking.html

Under Building a Router, it said...

"Even when FreeBSD is configured in this way, it does not completely 
comply with the Internet standard requirements for routers. It comes 
close enough for ordinary use, however."

Could someone advise, in what way FreeBSD doesn't comply with Internet
standard requirements for routers ? Which internet standard it might be
referencing to.

Thanks.