Inside Cisco IOS Software Architecture (CCIE Professional Development)

Packet Switching on a Shared Memory Router

Now that we've looked at the general hardware architecture of the shared memory routers and how IOS divides their memory, let's look at how IOS actually switches packets. IOS on shared memory routers supports the following:

• Process switching

• CEF switching

• Fast switching

There are three stages in IOS packet switching:

1. Receiving the packet

2. Switching the packet

3. Transmitting the packet

Receiving the Packet

Figure 3-2 illustrates the steps of the packet receive stage.

Figure 3-2. Receiving the Packet

Step 1.

The interface media controller detects a packet on the network media and copies it into a buffer ...