Document filter language.

babel.man

@@ -124,6 +124,81 @@ of this machine, but can be any unique 128-bit string.
 .TP
 .IR interface ...
 The list of interfaces on which the protocol should operate.
+.SH CONFIG FILE FORMAT
+The configuration file is a sequence of lines each of which specifies
+a filter entry.  Each of these lines has the following format:
+.IP
+.I filter selector... action
+.PP
+.I Filter
+specifies the filter to which this entry will be added, and can be one of
+.BR in ,
+.BR out ,
+or
+.BR redistribute .
+
+.I Selector
+specifies the conditions under which the given statement matches.  It
+can be one of
+.TP
+.BI ip " prefix"
+This entry only applies to routes in the given prefix.
+.TP
+.BI eq " plen"
+This entry only applies to routes with a prefix length equal to
+.BR plen .
+.TP
+.BI le " plen"
+This entry only applies to routes with a prefix length less or equal to
+.BR plen .
+.TP
+.BI ge " plen"
+This entry only applies to routes with a prefix length greater or equal to
+.BR plen .
+.TP
+.BI neigh " id"
+This entry only applies to routes learned from a neighbour with router-id
+.IR id .
+.TP
+.BI id " id"
+This entry only applies to routes originated by a router with router-id
+.IR id .
+.TP
+.BI proto " p"
+This entry only applies to kernel routes with kernel protocol number
+.IR p .
+.TP
+.BI if " interface"
+For an input filter, this specifies the interface over which the route
+is learned.  For an output filter, this specifies the interface over
+which this route is advertised.  For a redistribute statement, this
+specifies the interface over which the route forwards packets.
+.PP
+.I Action
+specifies the action to be taken when this entry matches.  It can have
+one of the following values:
+.TP
+.B allow
+Allow this route, without changing its metric (or setting its metric
+to 0 in case of a redistribute filter).
+.TP
+.B deny
+Ignore this route.
+.TP
+.BI metric " value"
+For an input or output filter, allow this route after increasing its metric by
+.IR value .
+For a redistribute filter, redistribute this route with metric
+.IR value .
+.TP
+.B inherit
+For a redistribute filter, redistribute this route with the metric
+provided by the kernel.
+.PP
+If
+.I action
+is not specified, it defaults to
+.BR allow .
 .SH EXAMPLES
 Let
 .B $IPv6
@@ -148,7 +223,14 @@ them into the routing domain as zero-cost external routes:
 On an access point, you'll probably want to redistribute some routes
 into Babel:
 .IP
-# babel -X $IPv6 \-C 'redistribute metric 256' $IPv6 eth1
+# babel \-C 'redistribute metric 256' \-X $IPv6 $IPv6 eth1
+.PP
+or
+.IP
+# babel \\
+    \-C 'redistribute proto 11 ip ::/0 le 64 metric 256' \\
+    \-C 'redistribute proto 11 ip 0.0.0.0/0 le 24 metric 256' \\
+    \-X $IPv6 $IPv6 eth1
 .PP
 .SH WIRED INTERFACES
 By default, the daemon optimises traffic on wired interfaces by
@@ -177,6 +259,9 @@ flag.  This is recommended if you are running Babel over bridge
 interfaces, since such interfaces will be detected as wired interfaces.
 .SH FILES
 .TP
+.B /etc/babel.conf
+The default location of the configuration file.
+.TP
 .B /var/lib/babel\-state
 The default location of the file storing long-term state.
 .SH SIGNALS