No way? Uhm, that very much depends on your definition of "your system". And HTTP may be stateless, TCP certainly isn't (not that statelessness matters). In the simplest case, you have a network like this:

                      ^-^-^-^-^-^-^                             ^-^-^-
+^-^-^-^
  +-------------+    /             \    +-----------------+    /      
+       \
  | Your server |===< Local network >===| Router/Firewall |===< Big Ba
+d World > 
  +-------------+    \             /    +-----------------+    \      
+       /
                      v-v-v-v-v-v-v                             v-v-v-
+v-v-v-v
[download]

So, treat a request coming from your local network as "your system", and if it comes via the "Router/Firewall", it comes from somewhere else. And you block it. Preferably at said Router/Firewall.

Now, your details may be different, but your problem seems more a networking (and in particular, a firewall configuration problem) to me, than a Perl issue.