martians, import and export
statements.
The action taken when no match is found is dependent on the context,
for instance import and export route filters
assume an all reject ; at the end a list.
A route will match the most specific filter that applies. Specifying more than one filter with the same destination, mask and modifiers will generate an error.
network [ exact | refines ]
network mask mask [ exact | refines ]
network masklen number [ exact | refines ]
all
default
host host
These are all the possible formats for a route filter. Not all of
these formats are available in all places, for instance the
host and default formats are not valid for
martians.
In most cases it is possible to specify additional parameters relevent
to the context of the filter. For example, on a martian
statement it is possible to specify the allow keyword, on
an import statement you can specify a preference, and on
a export you can specify a metric.
If no additional parameters are specified, any destination that falls in the range given by the network and mask is matched, the mask of the destination is ignored. If a natural network is specified, the network, any subnets, and any hosts will be match. The two optional modifiers cause the mask of the destination to be considered also:
0.0.0.0 mask 0.0.0.0
0.0.0.0 mask 0.0.0.0 exact
host mask 255.255.255.255 exact