LevelOne GTL-2691 - Manual (Page 622)

C HAPTER 18 | General IP Routing
IP Routing and Switching
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Figure 379: Virtual Interfaces and Layer 3 Routing
IP R OUTING AND S WITCHING
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
VLAN 1
VLAN 2
Inter-subnet traffic (Layer 3 switching)
Routing
Unt Untagged Unt Untagged
Tagged or Untagged Tagged or Untagged Tagged or Untagged Tagged or Untagged
Intra-subnet traffic (Layer 2 switching)