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CX11x, CX31x, CX710 (Earlier Than V6.03), and CX91x Series Switch Modules V100R001C10 Configuration Guide 12

The documents describe the configuration of various services supported by the CX11x&CX31x&CX91x series switch modules The description covers configuration examples and function configurations.
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This section describes the implementation of Static Routes.

Basics of Static Routes

A router forwards data packets based on routing entries containing route information. The routing entries can be manually configured or calculated by dynamic routing protocols. Static routes refer to the routes that are manually added to the routing table.

Static routes use less bandwidth than dynamic routes. No CPU resource is used for calculating or analyzing routing update. When a fault occurs on the network or the topology changes, static routes cannot automatically change and must be changed manually. The configuration of a static route includes destination IP address and mask, outbound interface and next-hop address, and preference.

Destination Address and Mask

The destination IPv4 address is expressed in dotted decimal notation. The mask can be expressed either in dotted decimal notation or by the mask length, that is, the number of consecutive 1s in the mask. For details about the destination IPv6 address and mask, see "Basic IPv6 Configurations - Principles - IPv6 Addresses" in the Configuration Guide - IP Service. When the destination and mask are set to all 0s, the default static route is configured. For details about the default static route, see Application of the Static Default Route.

Outbound Interface and Next-Hop IP Address

When configuring a static route, you can specify the outbound interface and the next-hop IP address based on outbound interfaces types.

  • Configure the outbound interface for point-to-point (P2P) interfaces. For a P2P interface, the next-hop address is specified after the outbound interface is specified. That is, the address of the remote interface (interface on the peer device) connected to this interface is the next-hop address. For example, the protocol used to encapsulate 10GE is the Point-to-Point protocol (PPP). The remote IP address is obtained through PPP negotiation. You need specify only the outbound interface.

  • Configure the next hop for Non Broadcast Multiple Access (NBMA) interfaces (for example, ATM interfaces). You need to configure the IP route and the mapping between IP addresses and link-layer addresses.

  • Configure the next hop for broadcast interfaces (for example, Ethernet interfaces) and virtual template (VT) interfaces. The Ethernet interface is a broadcast interface, and the VT interface can be associated with several virtual access (VA) interfaces. If the Ethernet interface or the VT interface is specified as the outbound interface, multiple next hops exist and the system cannot decide which next hop is to be used. Therefore, this configuration is not recommended.

Static Route Preference

Different static routes can be configured with different preferences. A smaller preference value indicates a higher priority of static routes. If you specify the same preference for the static routes to the same destination, you can implement load balancing among these routes. If you specify different preferences for the static routes, you can implement route backup among the routes. For details, see Load Balancing and Route Backup.

BFD for Static Routes

Different from dynamic routing protocols, static routes do not have a detection mechanism. As a result, when a link fault occurs on the network, the administrator needs to handle it. Bidirectional Forwarding Detection (BFD) for static route is introduced to bind a static route to a BFD session so that the BFD session can detect the status of the link where the static route resides.

  • When the BFD session that is bound to a static route detects a link fault, BFD reports the link fault to the Routing Management (RM) module. The RM module sets the route to inactive. The route is unavailable in the routing table.

  • When the BFD session that is bound to a static route detects that the faulty link is re-established, BFD reports a message to the RM module. The RM module sets the route to active. The route is available in the IP routing table.


For details about BFD, see "BFD Configuration - Principles" in the Configuration Guide - Reliability.

NQA for Static Routes

As mentioned previously, static routes do not have a dedicated detection mechanism. After a fault occurs, the corresponding static route is automatically deleted from the IP routing table. This condition delays the link switchover and can interrupt services for a comparatively long time. The network administrator must delete the corresponding static route to allow traffic to switch to an available path.

An effective method is required to detect faults in links related to static routes. BFD for static routes is applicable only to the scenario where both communicating devices support BFD. If either of the two communicating devices supports NQA, NQA for static routes can be used to detect faults in links where Layer 2 devices reside.

NQA for static routes refers to the association between a static route and an NQA test instance. The system can use the NQA test instance to check the link status. Then, according to the NQA test result, the system can determine an optimal route in time to prevent communication interruption and ensure service quality. NQA for static routes functions as follows:
  • If NQA detects a fault in the link, the system sets the static route to inactive. The route becomes unavailable and is deleted from the IP routing table.
  • If NQA finds that the link recovers, the system sets the static route to active. The route becomes available and is added to the IP routing table.

When a static route is associated with an NQA test instance, only ICMP test instances are used to test whether there are reachable routes between the source and destination.

Each static route can be associated with only one NQA test instance.

For details about NQA, see "NQA Configuration - Principles" in the Configuration Guide - Network Management.


On the network shown in Figure 7-5, each access switch provides access services for 10 users, and a total of 100 users are connected to the network. Because dynamic routing protocols are unavailable for communication between RouterB and users, static routes are configured on RouterB. For network stability, RouterC, functioning as the backup for RouterB, is configured with static routes to the same destination. RouterA, RouterB, and RouterC run a dynamic routing protocol to learn routes from each other. RouterB and RouterC import static routes using a dynamic routing protocol and have different costs for these static routes. After the configuration is complete, RouterA can use the dynamic routing protocol to learn routes destined for users from RouterB and RouterC. RouterA uses the link related to the static route with a lower cost as the active link and the other link as the standby link.

NQA for static routes is configured on RouterB. NQA tests are performed to check the active link of RouterB → SwitchA → SwitchC (SwitchD). If the active link fails, the corresponding static route is deleted from the routing table, and traffic diverts to the standby link of RouterC → SwitchB → SwitchC (SwitchD). If both links work properly, traffic travels along the active link.

Figure 7-5 Networking to apply NQA for 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 7-6, 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 7-6 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: 2019-08-09

Document ID: EDOC1000041694

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