Forwarding Principle

As shown in Figure 3-2, an Eth-Trunk is deployed at the data link layer, that is, between the LLC sub-layer and the MAC sub-layer.

Figure 3-2 Eth-Trunk in the Ethernet protocol stack

The Eth-Trunk forwarding table is composed of the following entries:

• HASH-KEY value

  The key value is calculated through the hash algorithm based on the MAC address or IP address in a data packet.

• Interface number

  Eth-Trunk forwarding entries are relevant to the number of member interfaces in an Eth-Trunk. Different HASH-KEY values map different outbound interfaces.

  If physical interfaces 1, 2, 3, and 4 are bundled into an Eth-Trunk, the Eth-Trunk forwarding table contains four entries and the HASH-KEY values correspond to interface numbers, as shown in Figure 3-3.

Figure 3-3 Example of an Eth-Trunk forwarding table

The Eth-Trunk module forwards a packet according to the Eth-Trunk forwarding table:

1. The Eth-Trunk module receives a packet from the MAC sub-layer, and then extracts its source MAC address/IP address or destination MAC address/IP address.

2. The Eth-Trunk module calculates the HASH-KEY value using the hash algorithm.

3. Based on the HASH-KEY value, the Eth-Trunk module searches the Eth-Trunk forwarding table for the interface number, and then sends the packet from the corresponding interface.