D-Link DFL-2500 User Guide - Page 108
Policy-based Routing Tables, Policy-based Routing Policy, PBR Execution
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10.7. Policy Based Routing(PBR) 89 • Creating provider-independent metropolitan area networks - All users share a common active backbone, but can use different ISPs, subscribing to different streaming media providers. PBR implementation in D-Link firewalls consists of two elements: • One or more named PBR tables in addition to the normal routing table. • A separate PBR ruleset, which determines which named routing table to use. 10.7.2 Policy-based Routing Tables Policy-based routing tables are alternative tables additional to the main routing table. These tables contain the same fields for describing routes as the main routing table, except that there is an Ordering parameter defined on each of them. This parameter dictates when the PBR table comes into play in firewall's route lookup, either prior or later than the main table. 10.7.3 Policy-based Routing Policy The rules defined in PBR policy are selectors of different routing tables. Each PBR rule is triggered by the fields of service type and source & destination interface and network. During the firewall's lookup, the first matching rule is carried out, and routes can be chosen and prioritized by the order parameter on a per-state basis other than packet-by-packet lookup, which means that PBR rules can specify which routing table to use in both forward and return direction. 10.7.4 PBR Execution The sequence of PBR execution cooperating with the main routing table and the firewall's rules setting can be summarized as follows: 1. Main routing table checking - looking up the interface for the packets' destination address. 2. Rules consulting - looking up in the firewall's Rules list to determine the action to the packets. 3. PBR policy consulting - If the lookup in step 2 results in allowing the packets to go through, the firewall will perform a lookup in the PBR D-Link Firewalls User's Guide
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