This section details JUNOS software routing policy operation and
configuration. The actual application of policy to solve some specific
networking requirement is generally left to the protocol-specific coverage
found in subsequent chapters. You configure policy-related options and
statements at the
hierarchy. Routing policy and firewall filters have a similar syntax in
JUNOS software. The former deals with routes in the control plane, whereas
the latter deals with packets in the data plane.
Simply put, routing policy is used to:
Control what routes are installed into the route table for possible selection as an active route
Control what routes are exported from the route table, and into which protocols
Alter attributes of routes, either at reception or at the time of advertisement to other peers
Given that routing policy is used to control the reception and transmission of routing information and to alter route attributes, it’s safe to say that you need routing policy when the default policy does not meet your requirements.
The specifics of the various default policies are covered later, but to provide an example, consider that, by default, directly connected routes are not advertised into any routing protocol; in the case of RIP, not even when RIP is configured to run on those directly connected interfaces. If your goal is to get direct routes advertised into RIP, the default policy obviously does not ...