Configuring OSPF

The Citrix ADC supports Open Shortest Path First (OSPF) Version 2 (RFC 2328). The features of OSPF on the Citrix ADC are:

• If a vserver is active, the host routes to the vserver can be injected into the routing protocols.
• OSPF can run on any subnet.
• Route learning advertised by neighboring OSPF routers can be disabled on the Citrix ADC.
• The Citrix ADC can advertise Type-1 or Type-2 external metrics for all routes.
• The Citrix ADC can advertise user-specified metric settings for VIP routes. For example, you can configure a metric per VIP without special route maps.
• You can specify the OSPF area ID for the Citrix ADC.
• The Citrix ADC supports not-so-stubby-areas (NSSAs). An NSSA is similar to an OSPF stub area but allows injection of external routes in a limited fashion into the stub area. To support NSSAs, a new option bit (the N bit) and a new type (Type 7) of Link State Advertisement (LSA) area have been defined. Type 7 LSAs support external route information within an NSSA. An NSSA area border router (ABR) translates a type 7 LSA into a type 5 LSA that is propagated into the OSPF domain. The OSPF specification defines only the following general classes of area configuration:
  • Type 5 LSA: Originated by routers internal to the area are flooded into the domain by AS boarder routers (ASBRs).
  • Stub: Allows no type 5 LSAs to be propagated into/throughout the area and instead depends on default routing to external destinations.

After enabling OSPF, you need to configure advertisement of OSPF routes. For troubleshooting, you can limit OSPF propagation. You can display OSPF settings to verify the configuration.

Enabling and Disabling OSPF

To enable or disable OSPF, you must use either the CLI or the GUI. When OSPF is enabled, the Citrix ADC starts the OSPF process. When OSPF is disabled, the Citrix ADC stops the OSPF routing process.

To enable or disable OSPF routing by using the CLI:

At the command prompt, type one of the following commands:

1. enable ns feature OSPF

2. disable ns feature OSPF

To enable or disable OSPF routing by using the GUI:

1. Navigate to System > Settings, in Modes and Features group, click Change advanced features.
2. Select or clear the OSPF Routing option.

Advertising OSPF Routes

OSPF enables an upstream router to load balance traffic between two identical virtual servers hosted on two standalone Citrix ADC appliances. Route advertising enables an upstream router to track network entities located behind the Citrix ADC.

To configure OSPF to advertise routes by using the VTYSH command line:

At the command prompt, type the following commands, in the order shown:

Example:

>VTYSH
NS# configure terminal
NS(config)# router OSPF
NS(config-router)# network 10.102.29.0/24 area 0
NS(config-router)# redistribute static
NS(config-router)# redistribute kernel

Limiting OSPF Propagations

If you need to troubleshoot your configuration, you can configure listen-only mode on any given VLAN.

To limit OSPF propagation by using the VTYSH command line:

At the command prompt, type the following commands, in the order shown:

Example:

>VTYSH
NS# configure terminal
NS(config)# router OSPF
NS(config-router)# passive-interface VLAN0

Verifying the OSPF Configuration

You can display current OSPF neighbors, and OSPF routes.

To view the OSPF settings by using the VTYSH command line:

At the command prompt, type the following commands, in the order shown:

Example:

>VTYSH
NS# sh ip OSPF neighbor
NS# sh ip OSPF route

Configuring Graceful Restart for OSPF

In a non-INC high availability (HA) setup in which a routing protocol is configured, after a failover, routing protocols are converged and routes between the new primary node and the adjacent neighbor routers are learned. Route learning take some time to complete. During this time, forwarding of packets is delayed, network performance might get disrupted, and packets might get dropped.

Graceful restart enables an HA setup during a failover to direct its adjacent routers to not remove the old primary node’s learned routes from their routing databases. Using the old primary node’s routing information, the new primary node and the adjacent routers immediately start forwarding packets, without disrupting network performance.

To configure graceful restart for OSPF by using the VTYSH command line, at the command prompt, type the following commands, in the order shown: