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S12700 V200R010C00 Configuration Guide - Device Management

This document describes the principles and configurations of the Device Management features, and provides configuration examples of these features.
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Cluster Link Aggregation and Local Preferential Forwarding

Cluster Link Aggregation and Local Preferential Forwarding

Cluster Link Aggregation

CSS supports cluster link aggregation (Eth-Trunk). You can bundle physical Ethernet interfaces on different member switches into an Eth-Trunk interface and connect a CSS to an upstream or downstream device through the Eth-Trunk link. If a member switch or a member link of the Eth-Trunk fails, data flows are forwarded through the cluster cables between the member switches. Cluster link aggregation ensures reliable data transmission and implements backup between member switches. It is important to the core switching system and networks with high QoS requirements because it prevents service interruptions caused by single-point failures and greatly improves network availability.

As shown in Figure 8-6, traffic sent to the core device on the network is equally distributed to member links of an Eth-Trunk set up between CSS member switches. When a member link fails, traffic on this link is distributed to the other link through the cluster cables between the member switches. This link backup mechanism improves network reliability.

Figure 8-6  Cluster link aggregation 1

As shown in Figure 8-7, traffic sent to the core device on the network is equally distributed to member links of an Eth-Trunk set up between CSS member switches. When a member switch fails, traffic toward this switch is distributed to the other switch. This device backup mechanism improves network reliability.

Figure 8-7  Cluster link aggregation 2

Local Preferential Forwarding

To implement reliable data traffic transmission and backup between member switches, a CSS usually connects to upstream and downstream devices through inter-chassis Eth-Trunk links. Similar to a standalone switch, a CSS uses the hash algorithm to select outbound interfaces in an inter-chassis Eth-Trunk. Therefore, traffic is load balanced among the Eth-Trunk member links, and some traffic is forwarded across the member switches.

Inter-chassis forwarding consumes bandwidth on cluster cables. As bandwidth provided by a cluster cable is limited, this forwarding mode increases load on cluster cables and reduces forwarding efficiency. To improve forwarding efficiency and reduce traffic on cluster cables, the switch provides the local preferential forwarding feature. This feature allows traffic reaching the local switch to be preferentially forwarded through a local interface. If the local device has no outbound interface or all the outbound interfaces fail, traffic is forwarded through an interface on another member switch.

As shown in Figure 8-8, SwitchA and SwitchB set up a CSS, and their uplink and downlink interfaces are bundled to Eth-Trunk interfaces. If local preferential forwarding is not configured, traffic reaching SwitchA is load balanced between the Eth-Trunk member links, and some traffic is forwarded through the cluster cables and sent out from a physical interface on SwitchB. If local preferential forwarding is configured, traffic reaching SwitchA is preferentially forwarded through a local physical interface and does not pass through the cluster cables.

Figure 8-8  Local preferential forwarding
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Updated: 2019-08-21

Document ID: EDOC1000142080

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