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Advanced Path Control Tools

This section provides a brief overview of additional path control mechanisms that you might encounter in your enterprise networks.

Cisco IOS Optimized Edge Routing

Cisco IOS OER is intended for sites using multiple Internet or WAN service providers. Cisco IOS OER uses tools such as Cisco IOS IP SLAs to automatically detect network service degradation and to make dynamic routing decisions and adjustments based on criteria such as response time, packet loss, jitter, path availability, traffic load distribution, and so forth.

In contrast, normal routing, using routing protocols, focuses on detecting a routing path using static routing metrics, rather than the condition of the service over that path.

An example is illustrated in Figure 5-13. The Cisco IOS OER edge routers, called border routers, monitor information about route prefixes (using traditional routing protocols) and gather performance statistics over each external interface (in this example, using Cisco IOS IP SLAs).

Figure 5-13

Figure 5-13 Cisco IOS OER Operations.

This information is periodically reported to another router called the master controller. If the prefixes and exit links comply with a configured policy based on performance and service metrics, routing remains as is. If not, the master controller makes a policy-based decision and notifies the border routers, which change the path, by such mechanisms as adding static routes or changing routing protocol parameters.


Virtualization is another advanced technology being used in enterprise networks that includes benefits such as traffic segregation across a common physical network infrastructure.

An example of virtualization is the use of virtual routing and forwarding (VRF) tables, which are virtual routing tables used to separate the routing function by group, on one physical router, as illustrated in Figure 5-14.

Figure 5-14

Figure 5-14 VRF Creates Separate Virtual Routing Tables in One Physical Router.

For example, employee routes could be kept separate from guest routes by using two different VRFs. These VRFs could also be associated with other virtualization and traffic segregation elements on the network, such as virtual LANs (VLANs), virtual private networks (VPNs), and generic routing encapsulation (GRE) tunnels, to provide an end-to-end, segregated path across the network. An example is illustrated in Figure 5-15, in which path control is based on a design decision to engineer different paths, end to end, with a variety of network virtualization technologies. In this figure, two business units are associated with two different VRFs on the end routers. These VRFs are associated with different VLANs and VPNs throughout the network, to provide an end-to-end segregated path across the network.

Figure 5-15

Figure 5-15 Virtualization Technologies Used for Path Control.

Cisco Wide Area Application Services

Cisco WAAS is a good example of the use of PBR to adjust the path of traffic based on advanced services for that traffic, to provide both scalability and high availability. Technologies such as Web Cache Communications Protocol (WCCP) perform a similar function, which is to have routers redirect normal traffic flows into Cisco WAAS devices, where a series of data reduction, flow optimization, and application acceleration services are implemented, and then have them route the flows back into their normal path across the WAN. This scenario is illustrated in the example in Figure 5-16. This use of path control is becoming common in networks with branch offices.

Figure 5-16

Figure 5-16 WCCP Used for WAN Optimization.

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