802.1Q bridges use what is called “ flood-and-learn” to populate the MAC forwarding table. If a packet is received without a VLAN tag, the bridge port has a default VLAN tag associated with it. Similarly, we’ll assume that L1 connects to host A on Port A.Īn 802.1Q bridge forwards a packet based on the VLAN and the destination MAC address of the packet. To simplify the mappings a reader has to maintain, we’ll refer to the MAC address of A as MAC A. In an 802.1Q bridge, these virtual networks will be VLANs. There are two virtual networks, red and blue. Hosts (or endpoints) A through F are attached to the leaves. The figure shows a simple Clos network with two spine switches labeled S1 and S2 and four leaf switches labeled L1 through L4. A compare-and-contrast table at the end helps solidify these concepts further.įor the sake of this discussion, let us assume the network shown inįigure 4-1. We then use this as the basis to describe how EVPN solves the same problem, albeit differently. We also introduce the terminology commonly used in bridging. ![]() ![]() IEEE 802.1Q defined the standard that describes how VLAN-aware bridges work, and so traditional bridging is also called 802.1Q bridging or plain. To understand how bridging works with EVPN, we begin with a quick study of how bridging works in a traditional 802.1Q bridge.
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