Document PacketAliasPptp() and allow it to be disabled

by passing INADDR_NONE.

lib/libalias/alias_db.c

@@ -1953,8 +1953,7 @@ PacketAliasPptp(struct in_addr src_addr)
 {
 
     pptpAliasAddr = src_addr; 		/* Address of the inside PPTP machine */
-    pptpAliasFlag = 1;
-
+    pptpAliasFlag = src_addr.s_addr != INADDR_NONE;
 
     return 1;
 }

lib/libalias/libalias.3

@@ -33,6 +33,7 @@ of the text.
     4.2 PacketAliasRedirectAddr()
     4.3 PacketAliasRedirectDelete()
     4.4 PacketAliasProxyRule()
+    4.5 PacketAliasPptp()
 5. Fragment Handling
     5.1 PacketAliasSaveFragment()
     5.2 PacketAliasGetFragment()
@@ -507,6 +508,7 @@ re-mapped in the same manner the header fragment
 was.  Fragments which arrive before the header
 are saved and then retrieved once the header fragment
 has been resolved.
+
 .Ss 4.4 PacketAliasProxyRule()
 
 .Ft int
@@ -594,6 +596,34 @@ This function is usually used to redirect outgoing connections for
 internal machines that are not permitted certain types of internet
 access, or to restrict access to certain external machines.
 
+.Ss 4.5 PacketAliasPptp()
+
+.Ft extern int
+.Fn PacketAliasPptp "struct in_addr addr"
+
+This function causes any
+.Em G Ns No eneral
+.Em R Ns No outing
+.Em E Ns No encapsulated
+.Pq Dv IPPROTO_GRE
+packets to be aliased using
+.Ar addr
+rather than the address set via
+.Fn PacketAliasSetAddress .
+This allows the uses of the
+.Em P Ns No oint
+to
+.Em P Ns No oint
+.Em T Ns No unneling
+.Em P Ns No rotocol
+on a machine on the internal network.
+.Pp
+If the passed address is
+.Dv INADDR_NONE
+.Pq 255.255.255.255 ,
+.Dv PPTP
+aliasing is disabled.
+
 .Ss 5.1 PacketAliasSaveFragment()
 
 .Ft int

sys/netinet/libalias/alias_db.c

@@ -1953,8 +1953,7 @@ PacketAliasPptp(struct in_addr src_addr)
 {
 
     pptpAliasAddr = src_addr; 		/* Address of the inside PPTP machine */
-    pptpAliasFlag = 1;
-
+    pptpAliasFlag = src_addr.s_addr != INADDR_NONE;
 
     return 1;
 }

sys/netinet/libalias/libalias.3

@@ -33,6 +33,7 @@ of the text.
     4.2 PacketAliasRedirectAddr()
     4.3 PacketAliasRedirectDelete()
     4.4 PacketAliasProxyRule()
+    4.5 PacketAliasPptp()
 5. Fragment Handling
     5.1 PacketAliasSaveFragment()
     5.2 PacketAliasGetFragment()
@@ -507,6 +508,7 @@ re-mapped in the same manner the header fragment
 was.  Fragments which arrive before the header
 are saved and then retrieved once the header fragment
 has been resolved.
+
 .Ss 4.4 PacketAliasProxyRule()
 
 .Ft int
@@ -594,6 +596,34 @@ This function is usually used to redirect outgoing connections for
 internal machines that are not permitted certain types of internet
 access, or to restrict access to certain external machines.
 
+.Ss 4.5 PacketAliasPptp()
+
+.Ft extern int
+.Fn PacketAliasPptp "struct in_addr addr"
+
+This function causes any
+.Em G Ns No eneral
+.Em R Ns No outing
+.Em E Ns No encapsulated
+.Pq Dv IPPROTO_GRE
+packets to be aliased using
+.Ar addr
+rather than the address set via
+.Fn PacketAliasSetAddress .
+This allows the uses of the
+.Em P Ns No oint
+to
+.Em P Ns No oint
+.Em T Ns No unneling
+.Em P Ns No rotocol
+on a machine on the internal network.
+.Pp
+If the passed address is
+.Dv INADDR_NONE
+.Pq 255.255.255.255 ,
+.Dv PPTP
+aliasing is disabled.
+
 .Ss 5.1 PacketAliasSaveFragment()
 
 .Ft int