ZyXEL ISG50-PSTN User Guide - Page 290

Chapter 14 Policy and Static Routes 14.1.2 What You Need to Know Policy Routing Traditionally, routing is based on the destination address only and the ISG50 takes the shortest path to forward a packet. IP Policy Routing (IPPR) provides a mechanism to override the default routing behavior and alter the packet forwarding based on the policy defined by the network administrator. Policy-based routing is applied to incoming packets on a per interface basis, prior to the normal routing. How You Can Use Policy Routing • Source-Based Routing - Network administrators can use policy-based routing to direct traffic from different users through different connections. • Bandwidth Shaping - You can allocate bandwidth to traffic that matches routing policies and prioritize traffic. You can also use policy routes to manage other types of traffic (like ICMP traffic) and send traffic through VPN tunnels. • Cost Savings - IPPR allows organizations to distribute interactive traffic on high-bandwidth, highcost paths while using low-cost paths for batch traffic. • Load Sharing - Network administrators can use IPPR to distribute traffic among multiple paths. • NAT - The ISG50 performs NAT by default for traffic going to or from the WAN interfaces. A routing policy's SNAT allows network administrators to have traffic received on a specified interface use a specified IP address as the source IP address. Note: The ISG50 automatically uses SNAT for traffic it routes from internal interfaces to external interfaces. For example LAN to WAN traffic. Static Routes The ISG50 usually uses the default gateway to route outbound traffic from computers on the LAN to the Internet. To have the ISG50 send data to devices not reachable through the default gateway, use static routes. Configure static routes if you need to use RIP or OSPF to propagate the routing information to other routers. See Chapter 15 on page 302 for more on RIP and OSPF. Policy Routes Versus Static Routes • Policy routes are more flexible than static routes. You can select more criteria for the traffic to match and can also use schedules, NAT, and bandwidth management. • Policy routes are only used within the ISG50 itself. Static routes can be propagated to other routers using RIP or OSPF. • Policy routes take priority over static routes. If you need to use a routing policy on the ISG50 and propagate it to other routers, you could configure a policy route and an equivalent static route. DiffServ QoS is used to prioritize source-to-destination traffic flows. All packets in the same flow are given the same priority. CoS (class of service) is a way of managing traffic in a network by grouping similar types of traffic together and treating each type as a class. You can use CoS to give different priorities to different packet types. 290 ISG50 User's Guide