H3C Technologies H3C S12500 Series Switches - Manual (Page 12)

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• MAC entries configured or learned in the data plane—The edge devices use the typical
source-MAC-based learning mechanism to learn unicast MAC addresses in their local sites (called
"local MAC addresses").
• MAC entries learned through EVI IS-IS—After completing neighbor discovery, the edge devices run
EVI IS-IS in the control plane to establish adjacencies and advertise MAC reachability information
that has been learned or configured in the data plane to each other over EVI links.
NOTE:
The mac-address max-mac-count command and the mac-address mac-learning enable command take
effect only on local MAC addresses, which are learned in the data plane. They do not take effect on
remote MAC addresses, which are learned in the control plane.
Unicast flow
For intra-site unicast flows, an edge device performs the typical MAC address table lookup, as shown
in Figure 4 .
Figure 4 Layer 2 forwarding in a site
The following forwarding process (see Figure 5 ) takes place for unicast flows between sites:
1. The source edge device learns the source MAC address of the incoming Ethernet frame, and looks
up the destination MAC address in its MAC table for the outgoing interface.
2. If the outgoing interface is an EVI-Link interface rather than an internal physical port, the source
edge device encapsulates the frame in a GRE header, and then adds an IP header and a link layer
protocol header.
In the outer IP header, the source IP address is the source edge device's tunnel source IP address,
and the destination IP address is the destination edge device's tunnel source IP address.