gated route filtering
Routes are filtered by specifying configuration language that will match a
certain set of routes by destination or by destination and mask. Among other
places, route filters are used on 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 of 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. The filtering syntax is as follows:
network network mask mask network mask-length number all host hostThese are all the possible formats for a route filter. Not all of these formats are available in all places; for instance, the host format is not valid for martians.
In most cases, it is possible to specify additional parameters relevant 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 an
export statement 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 match.
0.0.0.0 mask 0.0.0.0
host mask 255.255.255