User`s manual

EDS-828 Series User’s Manual Featured Functions
3-69
Using Layer 3 Settings
The EDS-828 is a Layer-3 switch that performs data switching on the Network Layer (Layer 3) of
the ISO’s OSI layer model. Unlike Layer-2 switching, which uses the MAC address for
exchanging data, a Layer-3 switch uses the IP address to represent 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-728
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
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Layer 3 Layer 3
Layer 4
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Layer 5
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Layer 6
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Layer 7
Layer 7
The Layer-3 Switching Concept
IP (Internet Protocol) is a protocol defined on layer 3 of the 7-layer OSI 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.
Since Layer 2 switches use the MAC address to determine the destination of transmitted data
packets, and Layer 3 switches use IP address, some mechanism is needed to associate MAC
addresses with IP addresses. This is done by ARP (Address Resolution Protocol), which creates a
table that matches MAC addresses to IP addresses.
When a PC sends out an ARP request, which is just a broadcast packet requiring the IP address
owner to send back his MAC address, two situations could occur:
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. There after 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 the IP address owner, your PC packs the data packet with the IP address, and
sends the packet to the Layer-3 switch (gateway/router) using its MAC address. The Layer-3
switch (gateway/router) receives the data packet, re-packs it, and then forwards it to the next
hop according to the routing rules.
Static Routing and Dynamic Routing
The EDS-828 supports two routing methods: static routing and dynamic routing. Dynamic routing
makes use of RIP V1 and V2. You can either choose one routing method, 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 a metric that represents the cost we
have to pay to access a different network.
Static Route
You can define the routes yourself by specifying what is the next hop (or router) that the EDS-828
forwards data for a specific subnet. The settings of the Static Route will be added to the routing
table and stored in the EDS-828.