Clavister cOS Core Administration Guide

Chapter 4: Routing
received routing information, and it might be crucial to avoid parts of the routing database
getting published to other routers.
For this reason, Dynamic Routing Rules are used to regulate the flow of routing information.
These rules filter either statically configured or OSPF learned routes according to parameters like
the origin of the routes, destination, metric and so on. The matched routes can be controlled by
actions to be either exported to OSPF processes or to be added to one or more routing tables.
Usage with OSPF
Dynamic Routing Rules are used with OSPF to achieve the following:
• Allowing the import of routes from the OSPF AS into local routing tables.
• Allowing the export of routes from a local routing tables to the OSPF AS.
• Allowing the export of routes from one OSPF AS to another OSPF AS.
Note
The last usage of joining asynchronous systems together is rarely encountered except in
very large networks.
OSPF Requires at Least an Import Rule
By default, cOS Core will not import or export any routes. For OSPF to function, it is therefore
mandatory to define at least one dynamic routing rule which will be an Import rule.
This Import rule specifies the local OSPF Router Process object. This enables the external routes
made available in the OSPF AS to be imported into the local routing tables.
Specifying a Filter
Dynamic routing rules allow a filter to be specified which narrows the routes that are imported
based on the network reached. In most cases, the Or is within option should be specified as
all-nets so that no filter is applied.
When to Use Export Rules
Although an Import rule is needed to import routes from the OSPF AS, the opposite is not true.
The export of routes to networks that are part of OSPF Interface objects are automatic.
A dynamic routing export rule must be created to explicitly export the route to the OSPF AS.
Dynamic Routing Rule Objects
The diagram below shows the relationship between the cOS Core dynamic routing rule objects.
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