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Cisco LAN Switching Fundamentals by Basir Sakandar - CCIE No. 6040, David Barnes - CCIE No. 6563

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Understanding the MLS Packet Flow

It is critical for the MLS-enabled switch to see the full initial packet flow. In other words, the switch must see the initial packet destined to the inbound router interface, and then, it must also see the packet on the outbound interface of the router. If the switch does not know the outbound interface for the flow of the traffic, it will not have the information to rewrite the MAC at the ASIC level.

As the packet enters the port destined to another VLAN, the switch will forward the packet to the RSM (see Figure 6-1). This is known as the Candidate packet. Assuming the switch sees the outbound interface, the packet now becomes an Enable packet. The RSM will do a MAC rewrite and forwards the packet out its ...

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