" LAN servers are restricted to all local clients ( class c ) " error is a common problem for everyone including myself, so I decided to come here for some help on this error for all to suggest how to fix it. Im having this problem on all mods and yes even the default game.
Here is my information

Half life installed : Yes
Version : 1.1.1.0 ( best version or so I heard )
Im hosting a : Dedicated Server
Net : Broadband Cable Modem No Router
Error : LAN clients are restricted to local clients class c
Used Hamachi? : Yes
Did it work? : No
Put sv_lan 1 in command parameter and server.cfg? : Yes
Did it work? : No
put sv_lan 0 instead sv_lan 1 : Yes
Did that work? : No
Clients Router? : No
Tried Other versions? : Yes
Did they work? : No

No problems with my girlfriends router at all it's the server im trying to host

Me and my girlfriend have tried virtually everything but it hasn't worked at all

I really need help on this, any help would be appreciated

any suggestions?