15 Route Map

Route maps provide a means to both filter and/or apply actions to route, hence allowing policy to be applied to routes.

Route-maps are an ordered list of route-map entries. Each entry may specify up to four distincts sets of clauses:

‘Matching Policy’

This specifies the policy implied if the ‘Matching Conditions’ are met or not met, and which actions of the route-map are to be taken, if any. The two possibilities are:

• - ‘permit’: If the entry matches, then carry out the ‘Set Actions’. Then finish processing the route-map, permitting the route, unless an ‘Exit Action’ indicates otherwise.
• - ‘deny’: If the entry matches, then finish processing the route-map and deny the route (return ‘deny’).

The ‘Matching Policy’ is specified as part of the command which defines the ordered entry in the route-map. See below.

‘Matching Conditions’

A route-map entry may, optionally, specify one or more conditions which must be matched if the entry is to be considered further, as governed by the Match Policy. If a route-map entry does not explicitely specify any matching conditions, then it always matches.

‘Set Actions’

A route-map entry may, optionally, specify one or more ‘Set Actions’ to set or modify attributes of the route.

‘Call Action’

Call to another route-map, after any ‘Set Actions’ have been carried out. If the route-map called returns ‘deny’ then processing of the route-map finishes and the route is denied, regardless of the ‘Matching Policy’ or the ‘Exit Policy’. If the called route-map returns ‘permit’, then ‘Matching Policy’ and ‘Exit Policy’ govern further behaviour, as normal.

‘Exit Policy’

An entry may, optionally, specify an alternative ‘Exit Policy’ to take if the entry matched, rather than the normal policy of exiting the route-map and permitting the route. The two possibilities are:

• - ‘next’: Continue on with processing of the route-map entries.
• - ‘goto N’: Jump ahead to the first route-map entry whose order in the route-map is >= N. Jumping to a previous entry is not permitted.

The default action of a route-map, if no entries match, is to deny. I.e. a route-map essentially has as its last entry an empty ‘deny’ entry, which matches all routes. To change this behaviour, one must specify an empty ‘permit’ entry as the last entry in the route-map.

To summarise the above:

‘action’

• - Apply set statements
• - If call is present, call given route-map. If that returns a ‘deny’, finish processing and return ‘deny’.
• - If ‘Exit Policy’ is next, goto next route-map entry
• - If ‘Exit Policy’ is goto, goto first entry whose order in the list is >= the given order.
• - Finish processing the route-map and permit the route.

‘deny’

• - The route is denied by the route-map (return ‘deny’).

‘cont’

• - goto next route-map entry