Discussion

then accept;
}
}
}
protocols {
ospf {
export send-statics;
}
}
Discussion
From a structural point of view, this routing policy is very straightforward and illustrates
the basic components of how to configure a policy. The JUNOS policy language
is similar to standard programming languages or pseudocode, so you can read
through the show output in this recipe to get the gist of the policy. If you are not a
programmer, you can read the policy language as if it were a paragraph written in an
outline format. Looking through the show output in this recipe, you see it creates a
policy named send-statics that looks for static routes and accepts them. OSPF
applies the policy to routes it advertises to its OSPF neighbors. Rephrased, this recipe
allows OSPF to advertise static routes in addition to the default OSPF behavior,
which is to advertise routes learned from OSPF.
Before looking at the policy configuration, one question you might ask is why you
need to create routing policies at all. What happens if you don’t configure any? By
default, all routing protocols accept any routes they learn from their protocol neighbors
or peers and place them into one of the routing tables (see Table 9-1). This
means that without a routing policy, BGP accepts all routes from all its BGP neighbors,
IS-IS accepts all routes from all its IS-IS neighbors, OSPF from all its OSPF
neighbors, and so on. Routing policy is how you modify this behavior. In most cases,
you use routing policy with BGP to enforce peering agreements and your company’s
administrative policies because they provide explicit control over which routes are
installed in the routing table. These routes are eligible to become active routes, which
are used for forwarding traffic. Routing policy also provides explicit control over
which routes are advertised to the router’s neighbors.
Table 9-1. Default routing-policy actions
Protocol Routing table Default import action Default export action
BGP inet.0 Accept all BGP routes. Do not modify
BGP route properties.
Accept and export active BGP routes. Do
not modify BGP route properties.
DVMRP inet.1 Accept all DVMRP routes. Accept and export active DVMRP routes.
IS-IS
inet.0 and
inet6.0
Accept all IS-IS routes. Policy cannot be
modified because IS-IS requires that all
routers in an area have the same linkstate
database to maintain a stable,
loop-free network.
Reject everything (IS-IS uses LSPs to
advertise its routes).
Creating a Simple Routing Policy | 285
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