connection limits

[=?x-user-defined?Q?toylet=2Elinux=5B=A4p=AA=B1=B7N=5D?=]

is there a maximum connection limit in the networking services of linux?
how could I find out all these limits? 
/usr/src/linux/include/limits.h?

a friend of mine running a public news server using dnews on freebsd.
and I constantly hit an error message "800 simultaneous connections
exceeded".


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