LevelOne GEL-5261, User Manual

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Chapter 17
| General IP Routing
IP Routing and Switching
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Figure 341: Virtual Interfaces and Layer 3 Routing
Inter-subnet traffic (Layer 3 switching)
Routing
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VLAN 1
VLAN 2
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Intra-subnet traffic (Layer 2 switching)
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:
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Layer 2 forwarding (switching) based on the Layer 2 destination MAC address
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Layer 3 forwarding (routing):
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Based on the Layer 3 destination address
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Replacing destination/source MAC addresses for each hop
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Incrementing the hop count
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Decrementing the time-to-live
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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.