User`s guide

252 XSR User’s Guide
VPN Applications Chapter 11
Configuring the Virtual Private Network
Configuring OSPF with Fail Over
In this scenario, the client initiates two tunnels to two servers which are
connected on their trusted sites. With alternative paths to the trusted network
behind the server (via the client's two tunnels), OSPF learns two paths of
identical costs but uses the first learned path.
Should the tunnel serving that path become non-functional, OSPF
recalculates the routes and uses the alternate path. The interval between link
failure and the switch to the new route depends on the following OSPF
parameters set on the VPN interfaces:
 hello-interval - This specifies how often hello packets are sent to the
neighbor.
 dead-interval - This sets the peak interval which may elapse without
receiving hello packet from the neighbor before the link is declared
non-operational.
Setting those parameters low will generate more traffic on the link but
guarantees faster detection of link failure. As shown in page 253, OSPF is
enabled on the following interfaces:
Server 1
Interfaces FastEthernet 1 and VPN 1
Server 2
Interfaces FastEthernet 1 and VPN 1
Client
Interfaces FastEthernet 1, VPN 1 and VPN 2.