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ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
OSPF Fast Convergence

OSPF Fast Convergence

OSPF fast convergence is an extended feature of OSPF to speed up the convergence of routes. It includes the following components:

  • Partial Route Calculation (PRC): calculates only those routes which have changed when the network topology changes.

  • An OSPF intelligent timer: can dynamically adjust its value based on the user's configuration and the interval at which an event is triggered, such as the route calculation interval, which ensures rapid and stable network operation.

    OSPF intelligent timer uses the exponential backoff technology so that the value of the timer can reach the millisecond level.

PRC

When a node changes on the network, this algorithm is used to recalculate all routes. The PRC calculation takes a long time and consumes too many CPU resources, which affects the convergence speed.

In route calculation, a leaf represents a route, and a node represents a router. Either an SPT or a leaf change causes a route change. The SPT change is irrelevant to the leaf change. PRC processes routing information as follows:

  • If the SPT changes, PRC processes the routing information of all leaves on a changed node.
  • If the SPT remains unchanged, PRC does not process the routing information on any node.
  • If a leaf changes, PRC processes the routing information on the leaf only.
  • If a leaf remains unchanged, PRC does not process the routing information on any leaf.

OSPF Intelligent Timer

On an unstable network, routes are calculated frequently, which consumes a great number of CPU resources. In addition, LSPs that describe the unstable topology are generated and transmitted on the unstable network. Frequently processing such LSAs affects the rapid and stable operation of the entire network.

To speed up route convergence on the entire network, the OSPF intelligent timer controls route calculation, LSA generation, and LSA receiving.

The OSPF intelligent timer works as follows:

  • On a network where routes are calculated repeatedly, the OSPF intelligent timer dynamically adjusts the route calculation based on user's configuration and the exponential backoff technology. The number of route calculation times and the CPU resource consumption are decreased. Routes are calculated after the network topology stabilizes.

  • On an unstable network, if a router generates or receives LSAs due to frequent topology changes, the OSPF intelligent timer can dynamically adjust the interval. No LSAs are generated or processed within an interval, which prevents invalid LSAs from being generated and advertised on the entire network.

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Updated: 2019-01-04

Document ID: EDOC1100059473

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