Can I configure only an OSPF non-backbone area on S series switches

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OSPF partitions an AS into different areas to resolve the problem of frequent LSDB updates and improve network efficiency. An area is regarded as a logical group, and each group is identified by an area ID. A switch, not a link, resides at the border of an area. A network segment or link belongs only to one area. The area to which each OSPF-enabled interface belongs must be specified.
On an OSPF network, the backbone area connects to all other OSPF areas and transmits inter-area routes. A single non-backbone area (for example, Area 3) can be configured to implement intra-area communication. However, if multiple non-backbone areas are configured, a backbone area is required to enable communication between the non-backbone areas.
Therefore, all devices on a small network can be added to Area 0 (the backbone area). You are advised not to configure a single non-backbone area.

Other related questions:
Can an S series switch correctly calculate routes when OSPF backbone areas are not continuous
For S series switches supporting OSPF, if OSPF backbone areas are not continuous, some areas may be unreachable and loops may occur on inter-area and external routes.

Configure OSPF special areas on S series switches
1. Configure a stub area. A stub area is a special area where ABRs do not flood received AS external routes, significantly reducing the routing table size and transmitted routing information of routers. A border area on an OSPF network is often configured as a stub area. For example, configure Area1 as a stub area. [SwitchA] ospf 1 [SwitchA-ospf-1] area 1 [SwitchA-ospf-1-area-0.0.0.1] stub [SwitchA-ospf-1-area-0.0.0.1] quit [SwitchA-ospf-1] quit Precautions: 1. To configure an area as a stub area, you must run the stub command on all the devices in this area. 2. To configure an area as a totally stub area, run the stub no-summary command on the ABR in this area and run the stub command on other devices in this area. This prevents the ABR from transmitting Type 3 LSAs to the stub area, making the area a totally stub area. 2. Configure an NSSA area. In an NSSA, an ABR does not flood AS external routes received from other areas, similar to the situation in a stub area. The difference is that an ABR can import and flood AS external routes to the entire OSPF domain. A border area connected to another AS on an OSPF network is often configured as an NSSA. For example, configure Area2 as an NSSA. [SwitchB] ospf 1 [SwitchB-ospf-1] area 2 [SwitchB-ospf-1-area-0.0.0.2] nssa [SwitchB-ospf-1-area-0.0.0.2] quit [SwitchB-ospf-1] quit Precautions: 1. To configure an area as an NSSA, you must run the nssa command on all the devices in this area. 2. To configure an area as a totally NSSA, run the nssa no-summary command on the ABR in this area and run the nssa command on other devices in this area. This prevents the ABR from transmitting Type 3 LSAs to the NSSA, making the area a totally NSSA.

Why OSPF on an S series switch does not preferentially select a route with a small cost value and through the backbone area
OSPF defined by RFC 2328 must be compatible with RFC 1583. As defined in RFC 2328, if "RFC1583 Compatibility" is disabled, the routes learned through common areas are preferred regardless of their costs when routes can be learned through common areas and the backbone area. This helps reduce the burden of the backbone area.

Can I configure OSPF authentication on an interface of an S series switch
Two S series switches supporting OSPF can only use primary interface IP addresses to establish an OSPF adjacency relationship. If secondary interface IP addresses are added to the OSPF configuration, corresponding routes can be advertised.

Differences between interface authentication and area authentication for OSPF on S series switches
Rules for OSPF authentication on S series switches supporting OSPF are as follows: If an interface is configured with authentication, the authentication method configured on the interface is used. If the authentication is set to null, the interface is not authenticated. If the interface is not configured with authentication (null does not indicate no configuration), area authentication is used. If the area is not configured with authentication either, no authentication is performed.

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