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CLI-based Configuration Guide - IP Unicast Routing

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document describes the concepts and configuration procedures of IP Service features on the device, and provides the configuration examples.
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Permanent Advertisement of Static Routes

Permanent Advertisement of Static Routes

Permanent advertisement of static routes provides a low-cost and simple link detection mechanism and improves compatibility between Huawei devices and non-Huawei devices. If service traffic needs to be forwarded along a specified path, you can ping the destination addresses of static routes to detect the link connectivity.

Link connectivity determines the stability and availability of a network. Therefore, link detection plays an important role in network maintenance. BFD, as a link detection mechanism, is inapplicable to certain scenarios. For example, a simpler and more natural method is required for link detection between different ISPs.

After permanent advertisement of static routes is configured, the static routes that cannot be advertised are still preferred and are added to the routing table in the following cases:

  • If an outbound interface configured with an IP address is specified for a static route, the static route is always preferred and added to the routing table regardless of whether the outbound interface is Up or Down.

  • If no outbound interface is specified for a static route, the static route is always preferred and added to the routing table regardless of whether the static route can be iterated to an outbound interface.

In this way, you can enable IP packets to be always forwarded through this static route. The permanent advertisement mechanism provides a way for you to monitor services and detect link connectivity.

A device enabled with this feature always stores static routes in its IP routing table, regardless of whether the static routes are reachable. If a path is unreachable, the corresponding static route may become a blackhole route.


In Figure 2-2, BR1, BR2, and BR3 belong to ISP1, ISP2, and ISP3 respectively. Between BR1 and BR2 are two links, Link A and Link B. ISP1, however, requires that service traffic be forwarded to ISP2 over Link A without traveling through ISP3.

Figure 2-2 Networking for applying permanent advertisement of static routes

The External Border Gateway Protocol (EBGP) peer relationship is established between BR1 and BR2. For service monitoring, a static route destined for the BGP peer (BR2) at is configured on BR1, and permanent advertisement of static routes is enabled. The interface that connects BR1 to BR2 is specified as the outbound interface of the static route. Then, the network monitoring system periodically pings to determine the status of Link A.

If Link A works properly, ping packets are forwarded over Link A. If Link A becomes faulty, although service traffic can reach BR2 over Link B, the static route is still preferred because permanent advertisement of static routes is enabled. Therefore, ping packets are still forwarded over Link A, but packet forwarding fails. This scenario is also applicable to BGP packets. That is, a link fault causes the BGP peer relationship to be interrupted. The monitoring system detects service faults as returned in the ping result and prompts maintenance engineers to rectify the faults before services are affected.

Updated: 2019-05-20

Document ID: EDOC1100034072

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