User guide

1042 Brocade 6910 Ethernet Access Switch Configuration Guide

53-1002581-01

IP Routing and Switching

FIGURE 337 Virtual Interfaces and Layer 3 Routing

IP Routing and Switching

IP Switching (or packet forwarding) encompasses tasks required to forward packets for both Layer

2 and Layer 3, as well as traditional routing. These functions include:

• Layer 2 forwarding (switching) based on the Layer 2 destination MAC address

• Layer 3 forwarding (routing):

• Based on the Layer 3 destination address

• Replacing destination/source MAC addresses for each hop

• Incrementing the hop count

• Decrementing the time-to-live

• Verifying and recalculating the Layer 3 checksum

If the destination node is on the same subnetwork as the source network, then the packet can be

transmitted directly without the help of a router. However, if the MAC address is not yet known to

the switch, an Address Resolution Protocol (ARP) packet with the destination IP address is

broadcast to get the destination MAC address from the destination node. The IP packet can then

be sent directly with the destination MAC address.

VLAN 1

VLAN 2

Inter-subnet traffic (Layer 3 switching)

Routing

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Intra-subnet traffic (Layer 2 switching)