are also put at the end (before the
.B _AFTER
rules), though this may change later.
+.TP
+.BI "impbind " bind-rule
+Add an entry to the implicit-bind rule list. When a program attempts to
+.BR connect (2)
+a socket without binding its local address first,
+.B noip
+consults this list to decide on the correct local address to assign.
+Each entry in the list has the form
+.RS
+.IP
+.I address-range
+.IR address | \c
+.B same
+.PP
+The rules are tried in order: if the remote address matches (in the same
+way as in an ACL entry) the address range on the left side of the rule,
+then the socket is bound to the address from the right side; if the
+address on the right is
+.B same
+then the remote address is used.
+.PP
+Three environment variables
+are consulted too:
+.BR NOIP_IMPBIND_BEFORE ,
+.BR NOIP_IMPBIND ,
+and
+.BR NOIP_IMPBIND_AFTER .
+The
+.B _BEFORE
+rules are inserted at the front of the list; the
+.B _AFTER
+rules are appended on the end. Currently, the rules in
+.B NOIP_IMPBIND
+are also put at the end (before the
+.B _AFTER
+rules), though this may change later.
+.RE
.PP
(Aside: An attempt to connect to a remote host may not be a hopeless failure,
even if a real IP socket is denied:
is a comma-separated list of entries of the form:
.IP
.BR + | \-
-.IR address \c
-.RB [ \- \c
-.IR address | \c
-.BR / \c
-.IR prefix-length ]| \c
-.BR local | any
+.I address-range
.RB [ : \c
-.IR port [ \c
-.BI \- \c
-.IR port ]]
+.IR port-range ]
.PP
(The spaces in the above are optional.)
.PP
-The leading sign says whether
-matching addresses should be
+The leading sign says whether matching addresses should be
.I accepted
.RB (` + ')
or
.I denied
.RB (` \- ').
.PP
-The IP-address portion may be any of the following
+The
+.I address-range
+portion may be any of the following.
.TP
.B any
Matches all addresses.
.IB address / prefix-length
Matches an address in the given network.
.PP
-The port portion may be omitted (which means `match any port'), or may
-be a single
+The
+.I port-range
+may be omitted (which means `match any port'), or may be a single
.I port
or a range
.IB port \- port