User`s manual

EDS-828 Series Featured Functions
3-72
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
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:
• 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.
• 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/V1c/V2, and OSPF. 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.
RIP (Routing Information Protocol)
RIP is a distance vector-based routing protocol that can be used to automatically build up a routing table in the
EDS-828.
The EDS-828 can efficiently update and maintain the routing table, and optimize the routing by identifying the
smallest metric and most matched mask prefix.