Amer Networks E5Web GUI - Manual (Page 272)

4.3. Policy-based Routing
Overview
Policy-based Routing (PBR) is an extension to the standard routing described previously. It offers
administrators significant flexibility in implementing routing decision policies by being able to
use different routing tables according to specified criteria.
Normal routing forwards packets according to destination IP address information derived from
static routes or from a dynamic routing protocol. For example, using OSPF, the route chosen for
packets will be the least-cost (shortest) path derived from an SPF calculation. Policy-based
routing means that routes chosen for traffic can be based on specific traffic parameters.
Policy-based routing allows the following to be possible:
• Source-based Routing
A different routing table may need to be chosen based on the source of traffic. When more
than one ISP is used to provide Internet services, policy-based routing can route traffic
originating from different sets of users through different routes.
For example, traffic from one address range might be routed through one ISP, whilst traffic
from another address range might be through a second ISP.
• Service-based Routing
A different routing table might need to be chosen based on the service. Policy-based routing
can route a given protocol such as HTTP, through proxies such as Web caches. Specific
services might also be routed to a specific ISP so that one ISP handles all HTTP traffic.
• User-based Routing
A different routing table might need to be chosen based on the user identity or the group to
which the user belongs.
This is particularly useful in provider-independent metropolitan area networks where all users
share a common active backbone but each can use different ISPs and subscribe to different
providers.
PBR Components
Policy-based routing implementation in cOS Core is implemented using two components:
• Additional Routing Tables
One or more user-defined alternate Routing Tables are created in addition to the standard
default main routing table.
• Routing Rules
One or more Routing Rules are created to determine which routing table to use for which
traffic.
Without routing rules, the main routing table is the default. However, an alternate routing
table can also be explicitly assigned as the default table for a given interface without the use
of rules.
Chapter 4: Routing
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