PT-7828 User’s Manual
Featured Functions
3-80
Using Layer 3 Settings
The PT-7828 is a Layer-3 switch uses the Network Layer (layer 3) of the ISO’s OSI layer model
for data switching. Unlike Layer-2 switching for which the MAC address is used for exchanging
data, a Layer-3 switch uses the IP address to determine the destination of a data packet.
Layer-2 switching
Layer-3 switching
Layer 1
Layer 1
Layer 1
Layer 2
Layer 2
Layer 2
EDS-7828
Layer 3
Layer 3
Layer 4
Layer 4
Layer 5
Layer 5
Layer 6
Layer 6
Layer 7
Layer 7
Layer 1
Layer 1
Layer 1
Layer 2
Layer 2
Layer 3
Layer 2
EDS-7828
Layer 3
Layer 3
Layer 4
Layer 4
Layer 5
Layer 5
Layer 6
Layer 6
Layer 7
Layer 7
The Layer-3 Switching Concept
IP (Internet Protocol) is a protocol defined on layer 3 of the OSI 7-layer model. The IP address is
used to address data packets on the Network Layer, and is not tied to the hardware of a device or
PC. The IP address can be assigned by the system operator or network administrator.
Whereas a layer 2 switch uses the MAC address of a network card to determine the destination of
data packets, a layer 3 switch uses IP address currently assigned to the network card to transmit
data packets. Switches use ARP (Address Resolution Protocol) to establish the relationship
between MAC addresses and IP addresses.
When a PC sends out an ARP request, which is a broadcast packet requiring the IP address owner
to send back his MAC address, one of two situations could be encountered:
y
If your PC and the IP address owner are on the same subnet, the IP address owner will use a
unicast packet, which contains his MAC address, to reply to your PC. Henceforth, your PC will
use this MAC address to transmit to the IP address owner directly.
y
If your PC and the IP address owner are not on the same subnet, your PC will not receive a
reply, so it will ask for the MAC address of the Layer-3 switch (gateway/ router). To transmit
data packets to IP address owner, your PC packs the data packet with IP address and sends this
packet to the Layer-3 switch (gateway/ router) with its MAC address. The Layer-3 switch
(gateway/ router) receives the data packet, and then repacks and forwards it to the next hop,
based on the routing rules.
Static Routing and Dynamic Routing
The PT-7828 supports both static and dynamic routing. Dynamic routing can use either RIP V1
and/or V2. You can either choose one of the routing methods, or combine the two methods to
establish your routing table.
A routing entry includes the following items: the destination address, the next hop address (which
is the next router along the path to the destination address), and the metric that gives the cost we
have to pay to access a different network.
Static Routing
You can define the routes yourself by specifying the next hop (or router) that PT-7828 should
forward data to for a specific subnet. The Static Route settings will be stored in the PT-7828’s
routing table.
RIP (Routing Information Protocol)
RIP is a distance vector-based routing protocol that can automatically build up a routing table in
