Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?


How to Enable Link Delay Measurement and Advertising in OSPF

Understanding Link Delay Measurement and Advertising in OSPF

Benefits of link delay measurement and advertising in OSPF

Link delay measurement and advertising in OSPF provides the following benefits:

  • Highly beneficial in certain networks such as stock market data providers, where it is crucial to have access to market data in real-time to make trades faster than the competition. This is where network performance criteria or latency is becoming critical to data-path selection.
  • Helps to make path-selection decisions based on performance data (such as latency) in a cost-effective and scalable way.
  • Superior alternative to using metrics such as hop count or cost as routing metrics.

Overview of link delay measurement and advertising in OSPF

Network performance is measured by using TWAMP -Light. Starting in Junos OS Release 21.4R1, you can get the measurement of various performance metrics in IP networks, by using probe messages. OSPF Traffic Engineering Extensions helps to distribute network-performance information in a scalable fashion. This information can then be used to make path-selection decisions based on network performance.

Border Gateway Protocol Link-State (BGP-LS) allows BGP to carry link-state information acquired from IGPs, which then allows internet service providers (ISP) to selectively expose the information with other ISPs, service providers, CDNs and so on, through normal BGP peering. New BGP-Link State (BGP-LS) TLVs are defined to carry the IGP Traffic Engineering Metric Extensions.

The following illustration depicts the minimum IGP metric and minimum delay metric in networks that consist a core, metro, and access network.

In this scenario, core network is cheaper but has longer delay. Access shortcut, with lowest latency is expensive. As core network is cheaper, majority of traffic typically go from 1>2>3>4>5> to 6 by using minimum IGP metric. As displayed in scenario a), you can achieve minimum IGP requirement by running OSPF with appropriate cost configured and default OSPF algorithm set to zero. In businesses where ultra-low latency is crucial, packets need to go from 1 to 6. As displayed in scenario b), you can achieve minimum delay metric by defining OSPF flex algorithm with minimum latency, which minimize the delay to the endpoint. This flex algorithm consists only node 1 and node 6.

Configuring OSPF Link Delay on an OSPF Interface

In IP networks, the bulk of traffic often goes through the core network, which reduces costs but might result in increased latency. Business traffic, however, often benefits from the ability to make path-selection decisions based on other performance metrics, such as path latency, rather than relaying on the traditional path optimization based simply on IGP metrics. Optimizing a path to reduce latency can greatly benefit applications like real-time voice and video. It can also enable high performance access to financial market data where milliseconds can translate into significant gains or losses.

Starting in Junos OS Release 21.4R1, you can enable OSPF link delay in IP networks. You can achieve minimum IGP metric paths by configuring OSPF with the appropriate link cost using the default OSPF algorithm. Doing so optimizes paths to the endpoint that are based strictly on the sum of the link metrics. By using the OSPF delay flex algorithm you can optimize paths based on their end-to-end delay.

Link delay can be dynamically measured using Two-Way Active Measurement Probes (TWAMP). The routers then flood their link delay parameters. The routers in the area store these parameters in the shared Link State Database (LSDB). Ingress nodes run an SPF algorithm against the LSDB to compute paths that are optimized on various attributes, such as link colors, IGP metric, traffic-engineering (TE) metric.

To configure link delay measurement for an OSPF Interface:

  1. Create an OSPF area.

    For example:

  2. Specify the interface.

    For example:

  3. Configure dynamic OSPF link delay-measurement on the OSPF interface of the device.
  4. Configure the delay-measurement advertisement on the OSPF interface of the device. You can either configure accelerated or periodic advertisement.

    Accelerated advertisement is disabled by default. To configure accelerated advertisement, configure the threshold percentage.

  5. To configure periodic advertisement, you can either configure interval or the threshold percentage.

    For example: To configure periodic interval:

    For example: To configure periodic threshold:

  6. (Optional) Specify the probe count.

    For example:

  7. (Optional) Specify the probe interval.

    For example:

  8. Enter commit from the configuration mode.

To configure delay metric for an OSPF Interface:

For example:

Enter commit from the configuration mode.

To verify your configuration results, use the show protocols operational command.

user@host# show protocols

To verify that link delay parameters are present in the OSPF database use the show ospf database extensive | match delay operational command.

The output displays the delay of 20000 microseconds that is configured on the interface.