Nokia IPSO 4.0 manual Understanding Monitored-Circuit Vrrp, Configuring Vrrp, 186

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Understanding Monitored-Circuit VRRP

The Nokia implementation of VRRP includes additional functionality called monitored circuit. Monitored-circuit VRRP eliminates the black holes caused by asymmetric routes that can be created if only one interface on the master fails (as opposed to the entire box failing). IPSO does this by releasing priority over all of the VRRP-configured interfaces to allow the backup to take over entirely.

Note

You can choose to implement the industry standard VRRPv2 on your Nokia appliance instead of monitored-circuit VRRP. For information on implementing VRRPv2, see “Configuring VRRPv2” on page 196.

To understand the advantage of monitored-circuit VRRP, consider the configuration pictured in Figure 2. In this example, if you are using standard VRRPv2 and the external interface fails or becomes unreachable, the external virtual router fails over to the backup while the internal virtual router stays on the master. This can result in reachability failures, as the platform might accept packets from an internal end host but be unable to forward them to destinations that are reached through the failed interface to the external network.

Monitored-circuit VRRP monitors all of the VRRP-configured interfaces on the platform. If an interface fails, the master releases its priority over all of the VRRP-configured interfaces. This allows the backup platform to take over all of the interfaces and become master for both the internal and external VRID.

To release the priority, IPSO subtracts the priority delta, a Nokia-specific parameter that you configure when you set up the VRID, from the priority to calculate an effective priority. If you configured your system correctly, the effective priority is lower than that of the backup routers and, therefore, the VRRP election protocol is triggered to select a new master.

Configuring VRRP

You can configure VRRP on your appliance using three methods:

„Monitored-Circuit VRRP simplified method

For most purposes, you should use this method. This is a simplified version of the VRRP with monitored circuit full configuration method. You cannot use both full and simplified methods to configure monitored-circuit VRRP on the same appliance. For more information, see “Configuring Monitored-Circuit VRRP using the Simplified Method”.

„Monitored-Circuit VRRP full method

Use this method if you are working with a system on which VRRP has already been configured using this method or if you need control over the configuration of each individual interface. For more information see “Configuring Monitored-Circuit VRRP using the Full Method”.

„VRRPv2

186 Nokia Network Voyager for IPSO 4.0 Reference Guide