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CLI-based Configuration Guide - IP Unicast Routing

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R009

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Load Balancing and Route Backup

Load Balancing and Route Backup

When multiple routes have the same routing protocol preference and metric, these routes are called equal-cost routes, among which load balancing can be implemented. When multiple routes have different routing protocol preferences and metrics, route backup can be implemented among these routes.

Load Balancing

Routers support the multi-route mode, which allows you to configure multiple routes with the same destination and preference. If the destinations and costs of multiple routes discovered by the same routing protocol are the same, load balancing can be performed among the routes.

During load balancing, a router forwards packets based on the packets' 5-tuple (source IP address, destination IP address, source port, destination port, and transport protocol). When the 5-tuple information is the same, the router always chooses the next-hop address that is the same as the last one to send packets. When the 5-tuple information is different, the router forwards packets over idle paths.

Figure 1-2 Networking diagram of load balancing

In the example shown in Figure 1-2, RouterA forwards the first packet P1 to through GE1/0/0 and needs to forward subsequent packets to and respectively. The forwarding process is as follows:

  • If RouterA finds that 5-tuple information of P2 destined for is the same as that of P1 destined for, it forwards P2 and subsequent packets destined for through GE1/0/0.

  • If RouterA finds that 5-tuple information of P1 destined for is different from that of P1 destined for, it forwards P1 and subsequent packets destined for through GE2/0/0.

The number of equal-cost routes for load balancing varies with products.

Route Backup

Route backup can improve network reliability. You can configure multiple routes to the same destination as required. The route with the highest preference functions as the primary route, and other routes with lower preferences function as backup routes.

A router generally uses the primary route to forward data. When the primary link fails, the primary route becomes inactive. The router selects a backup route with the highest preference to forward data. In this manner, data is switched from the primary route to a backup route. When the primary link recovers, the router selects the primary route to forward data again because the primary route has the highest preference. Data is then switched back from the backup route to the primary route.

Updated: 2019-12-27

Document ID: EDOC1000174069

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