You have now been exposed to various applications of JUNOS software routing policy, here and in earlier chapters. We discussed the operational theory of routing policy in detail in Chapter 3. In summary, import routing policy is responsible for placing routes into the route table, possibly with modified attributes, and export policy is responsible for placing copies of routes into outgoing routing protocol updates, again possibly with modified attributes. The complexity of an organization’s policy is typically tied directly to the degree of its interconnectivity requirements. An enterprise that is single-homed needs very little policy; in most cases, such an attachment does not even warrant use of BGP!
This section focuses on applying JUNOS software routing policy to meet the needs of an enterprise that is dual-homed to different providers.
In a majority of cases, a dual-homed enterprise network will have distinctly different inbound and outbound policies. Your inbound policy is intended to control how traffic enters your AS from other networks, whereas your outbound policy dictates how traffic leaves your AS to enter other networks. You use specific instances of export and import policy to facilitate your organization’s inbound and outbound policy goals.
Achieving your inbound policy goals can be difficult, or even impossible, given that you do not have direct control over the outbound policies of the networks that you ...