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Single-homed port is a port on the MLAG peer device which provides access device single-access to the network through either MLAG Node 0 or Node 1 device. The single-homed port on the MLAG peer devices can connect to both hosts or servers and it can also be connected to other access switch devices. As shown in Figure 6, Switch 1 and Switch 3 are single-homed devices, the ports on the MLAG peer devices connected to Switch 1 and Switch 3 are called single-homed ports. Traffic between Switch1 and Switch3 always crosses the MLAG peer-link as Switch1 and Switch3 are active on different switches. With single-homed ports, servers and other standalone switches are able to single-home into the network.
Figure 6. MLAG network
The MAC address entries learned on the single-homed port will be synchronized to the MLAG peer-link port on the MLAG peer device, and the address type is Peer-Sync in the MAC address table. However, the MAC synchronization on the single-homed port will be done only when the MLAG neighbor state is ESTABLISHED. This MAC synchronization ensures that the devices connected to the single-homed port can communicate normally.
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As shown in the figure below, Switch 1 and Switch 2 are a pair of MLAG devices. The host can dual-access to the network through the MLAG peer devices. VRRP is not deployed in this topology.
Let’s assume that the default gateway address on the host is the address of Switch 2. In this case, any message from the host directly sent to Switch 2 can be routed correctly. However, there may exist one case that message from the host is hashed to Switch 1, Switch 1 finds that the destination MAC address of the message is Switch 2, then the message will be forwarded to Switch 2 through the peer link. When the message received from the peer link is about to be forwarded on the MLAG member port on Switch 2, it will be dropped due to MLAG flood control mechanism.
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