Preferential Forwarding of Local Traffic on an Eth-Trunk in a Stack
Concepts
Stack device
The stack device is a logical device formed by connecting multiple devices through dedicated stack cables. In Figure 3-10, DeviceB and DeviceC are connected to form a logical device.
Inter-device Eth-Trunk
An inter-chassis Eth-Trunk contains physical interfaces of multiple devices in a stack. When a device in the stack fails or a physical interface added to the Eth-Trunk fails, traffic can be transmitted between devices through stack cables. This ensures reliable transmission and implements device backup.
Preferential forwarding of local traffic
In network b of Figure 3-10, traffic from DeviceB or DeviceC is only forwarded through local member interfaces when the network runs properly. In network a of Figure 3-10, traffic is forwarded across devices through stack cables.
Inter-Device Eth-Trunk Supporting Preferential Forwarding of Local Traffic
Inter-chassis Eth-Trunk supporting preferential forwarding of local traffic saves bandwidth resources between devices and improves traffic forwarding efficiency. In a stack, an Eth-Trunk is configured to be the outbound interface of traffic to ensure reliable transmission. Eth-Trunk member interfaces are located on different devices. If preferential forwarding of local traffic is not enabled, when the stack device forwards traffic, the Eth-Trunk may select inter-device member interfaces based on the hash algorithm. This forwarding mode occupies bandwidth resources between devices and reduces traffic forwarding efficiency.
As shown in Figure 3-10, DeviceB and DeviceC constitute a stack, and the stack connects to DeviceA through an Eth-Trunk. After the Eth-Trunk in the stack is configured to preferentially forward local traffic, the following functions are implemented:
Forwarding received traffic by the local device
When DeviceB has Eth-Trunk member interfaces and the member interfaces function properly, the Eth-Trunk forwarding table of DeviceB contains only local member interfaces. In this manner, the hash algorithm selects a local member interface, and traffic is only forwarded through DeviceB.
Forwarding received traffic by another device
When DeviceB does not have any Eth-Trunk member interface or all member interfaces are faulty, the Eth-Trunk forwarding table of DeviceB contains all available member interfaces. In this manner, the hash algorithm selects a member interface on DeviceC, and traffic is forwarded through DeviceC.
- This function is only valid for known unicast packets, and is invalid for unknown unicast, broadcast, and multicast packets.
- Before configuring an Eth-Trunk to preferentially forward local traffic, ensure that member interfaces of the local Eth-Trunk have sufficient bandwidth to forward local traffic; otherwise, traffic may be discarded.