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Configuring OSPF in Data Center Networks

Munachimso Victor Nwaiwu

• 3 min read
Configuring OSPF in Data Center Networks

In our previous blogs, we explored the fundamental concepts of OSPF and delved into some of its key details. Now, we'll demonstrate how to configure OSPF in a data center environment, using Cisco Nexus devices as our example platform.

A Brief Overview of OSPF

OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP) used to propagate routing information within an autonomous system (AS).

Before we dive into configuration, let's recap some essential OSPF concepts:

  • Neighbor Relationships: OSPF routers form neighbor relationships (adjacencies) to exchange routing information.
  • Areas: OSPF networks can be divided into areas to improve scalability and efficiency.
  • DR/BDR Election: In multi-access networks, a Designated Router (DR) and a Backup Designated Router (BDR) are elected to optimize communication.

OSPF Versions

OSPF has two versions:

  • OSPFv2: Used for IPv4 networks.
  • OSPFv3: Used for IPv6 networks.

On Cisco Nexus switches, OSPFv2 is strictly for IPv4 and OSPFv3 is strictly for IPv6.

OSPFv2 Configuration

Here are the basic commands needed to configure OSPFv2 (and OSPFv3 with minor adjustments) on a Nexus switch:

  • feature ospf - Enables the respective ospf feature on the nexus switch.
  • router ospf instance_ID - Enables the ospf instance. The instance_ID  could be any alphanumeric string. It allows you to run multiple OSPF instances in parallel.
router ospf MyOSPFInstance
  • router_id router_ID - Configures the router id for the router. It is the name the router is referred to as in an OSPF domain
router-id 192.168.1.1
  • log-adjacency-changes - Enables system logging of neighbor state changes
  • ip router ospf instance_ID area area_ID (interface command) - Includes a specific interface to participate in a ospf process for a specific area
interface Ethernet1/1
 ip router ospf MyOSPFInstance area 0
  • auto-cost reference-bandwidth bandwidth [Gbps | Mbps] - Sets the reference bandwidth that is used for metric calculation. The default reference bandwidth is 40 Gbps.

Example (to set the reference bandwidth to 100 Gbps): 

auto-cost reference-bandwidth 100 Gbps
  • network address wildcard-mask area area_ID (older command) - This command is used to tell the router which networks should participate in OSPF. It is an alternative to configuring OSPF directly on specific interfaces as this command would enable OSPF on interfaces with addresses configured in the range of the given network. The network command is hidden (i.e., it won't be found when using TAB completion or '?'), but it still functions correctly.

Example (to advertise the network 192.168.1.0/24 in area 0): 

network 192.168.1.0 0.0.0.255 area 0

Below is the code block for the needed commands:

feature ospf 
router ospf MyOSPFInstance
 router-id 192.168.1.1
 log-adjacency-changes
 auto-cost reference-bandwidth 100 Gbps
!
interface Ethernet1/1
 ip router ospf MyOSPFInstance area 0
!
network 192.168.1.0 0.0.0.255 area 0 

NOTE: The configuration for v2 and v3 are virtually the same thing wIth the exception that “ospf” is used for v2 and “ospfv3” is used for v3

Although there are more configuration commands that could be used to manipulate the OSPF behaviours, the commands highlighted are very sufficient to deploy OSPF in a data center when applied

Verification

You can verify your OSPF configuration using commands like:

  • show ip ospf neighbor: Displays OSPF neighbor status.
  • show ip ospf database: Shows the OSPF routing table.

Conclusion

And there you have it! You've now successfully configured OSPF on your Cisco Nexus switches, enabling efficient routing within your data center network. This blog post concludes our mini-series on OSPF, where we covered the fundamentals, key details, and finally, the configuration steps.

But the journey through the world of networking doesn't stop here. In our next blog post, we'll move on to another critical routing protocol: BGP (Border Gateway Protocol). BGP is the glue that holds the internet together, enabling routing between different autonomous systems. So, stay tuned as we explore the intricacies of BGP and learn how to configure it in your network.

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