Technical data

Gateway Routing Daemon (GATED) Configuration Reference
A.18 Control Statements
A.18 Control Statements
The control statements are used to define:
• Route filtering, described in Section A.18.1
• Matching AS paths, as described in Section A.18.2
• Importing routes, as described in Section A.18.3
• Exporting routes, as described in Section A.18.4
• The source of exported routes, as described in Section A.18.5
• Route aggregation, as described in Section A.18.6
A.18.1 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, and in 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.
Filtering syntax:
network [ exact | refines | between number and number ]
network mask mask [ exact | refines | between number and number ]
network masklen number [ exact | refines | between number and number ]
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
an export you can specify a metric.
Each control statement is described in the following list:
•
network [ exact | refines | between lownumber and highnumber ] network
mask mask [ exact | refines | between lownumber and highnumber ]] network
masklen number [ exact | refines | between lownumber and highnumber ]
Matching usually requires both an address and a mask, although the mask is
implied in the shorthand forms listed below. These three forms vary in how
the mask is specified. In the first form, the mask is implied to be the natural
mask of the network. In the second, the mask is explicitly specified. In the
third, the mask is specified by the number of contiguous one bits.
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:
A–32 Gateway Routing Daemon (GATED) Configuration Reference