Characteristics of the Backup Methods

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Backup Interface

Floating Static Route

Dialer Watch

Dependent on line protocol status of primary interface and requiresthat the primary interface go down

Employs static routes with higher administrative distance to trigger DDR call

Watches specific routes in the routing table and initiates backup link if the route is missing

Encapsulation is a factor. For example, Frame Relay backup may not work correctly with backup interface.

Encapsulation independent

Encapsulation independent

Does not consider end-to-end connectivity. Problems with end-to-end connectivity, such as routing errors, do not trigger backup links.

Evaluates status of primary link based on the existence of routes to the peer. Hence, it considers primary link status based on the ability to pass traffic to the peer.

Evaluates status of primary link based on the existence of routes to the peer. Hence, it considers primary link status based on the ability to pass traffic to the peer.

Needs interesting traffic to trigger dialing the backup link.

Needs interesting traffic to trigger dialing the backup link even after the route to the peer is lost

Does not rely on interesting packets to trigger dialing. Dialing the backup link is done immediately when the primary route is lost.

Does not depend on the Routing protocol

Dependent on the routing protocol convergence time

Dependent on the routing protocol convergence time

Routing protocol independent

All routing protocols supported

EIGRP/OSPF supported

Limited to one router, one interface

Typically limited to single router, but with multiple interface/networks

Supports multiple router backup scenario. For example, one router monitors the link between two other routers and initiates the backup if that link fails

Can be used to provide bandwidth on demand. The backup interface can be setup to activate when the primary link reaches a specified threshold.

Bandwidth on demand is not possible since the route to the peer will exist regardless of the load on the primary link.

Bandwidth on demand is not possible since the route to the peer will exist regardless of the load on the primary link.

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Cisco CCIE Prep v1.0—Module 3-72

This table summarizes the characteristics of the three backup methods. You can use it to compare and evaluate the appropriate backup method to use in a certain situation.

Table 3-1: Backup Methods

Backup Interface

Floating Static Route

Dialer Watch

Dependent on line protocol status of primary interface and requires that the primary interface go down

Employs static routes with higher administrative distance to trigger DDR call when dynamic routes are lost

Watches specific routes in the routing table and initiates backup link if the route is missing

Encapsulation is a factor. For example, Frame Relay backup may not work correctly with backup interface.

Encapsulation independent

Encapsulation independent

■ Does not consider end-to-end connectivity

■ Problems with end-to-end connectivity, such as routing errors, do not trigger backup links

■ Evaluates status of primary link based on the existence of routes in the routing table

■ It considers primary link status based on the ability to route traffic to the peer

Evaluates status of primary link based on the existence of routes in the routing table

■ It considers primary link status based on the ability to route traffic to the peer

Requires interesting traffic to trigger dialing the backup link

Needs interesting traffic to trigger dialing the backup link even after the route to the peer is lost

Does not rely on interesting packets to trigger dialing

■ Dialing the backup link is done immediately when the primary route is lost

Does not depend on the routing protocol

Dependent on the routing protocol convergence time

Dependent on the routing protocol convergence time

Routing protocol independent

All routing protocols supported

Only Enhanced Interior Gateway Routing Protocol (EIGRP) and OSPF are supported

Limited to one router, one interface

Typically limited to single router, but with multiple interface/networks

■ Supports multiple router backup scenario

■ For example, one router monitors the link between two other routers and initiates the backup if that link fails.

■ Can be used to provide Bandwidth On Demand (BOD)

■ The backup interface can be setup to activate when the primary link reaches a specified load threshold.

Bandwidth on demand is not possible since the route to the peer will exist regardless of the load on the primary link.

Bandwidth on demand is not possible since the route to the peer will exist regardless of the load on the primary link

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