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DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
function as a layer 2 VLAN and would require an external router to connect to the rest of the
network.
6. Develop a policy scheme. Some subnets will have a greater need for multicasting bandwidth, for
example. A policy is a mechanism to alter the normal packet forwarding in a network device,
and can be used to intelligently allocate bandwidth to time-critical applications such as the
integration of voice, video, and data on the network.
7. Develop a redundancy scheme. Planning redundant links and routes to critical network
resources can save valuable time in the case of a link or device failure. The DES-3326’s
Spanning Tree function can be used to block the redundant link until it is needed.
VLAN Layout
VLANs on the DES-3326 have more functions than on a traditional layer 2 switch, and must therefore
be laid-out and configured with a bit more care. Layer 3 VLANs (VLANs that have an IP interface
assigned to them) can be thought of as network links – not just as a collection of associated end users.
Further, Layer 3 VLANs are assigned an IP interface address and subnet mask to enable IP routing
between them.
IEEE 802.1Q VLANs must be configured on the switch before they can be assigned IP interface
addresses or subnet masks. Further, the static VLAN configuration is specified on a per port basis. On
the DES-3326, a VLAN can consist of end-nodes – just like a traditional layer 2 switch, but a VLAN can
also consist of a subnetwork defined by an IP interface address and a subnet mask.
The IP subnets for the network must be determined first, and the VLANs configured on the switch to
accommodate the IP subnets. Finally, the IP subnets can be assigned to the VLANs.
Assigning IP Interface Addresses and Subnet Masks to VLANs
The DES-3326 allows the assignment of IP subnets to individual VLANs. Any VLAN configured on the
switch that is not assigned an IP subnet, will behave as a layer 2 VLAN and will not be capable of IP
routing – even if the switch is in IP Routing mode.
Developing an IP addressing scheme is a complex subject, but it is sufficient here to mention that the
total number of anticipated end nodes – for each Layer 3 VLAN – must be accommodated with a unique
IP address. It should be noted that the switch regards a VLAN with an IP interface address and
corresponding subnet mask assigned as an IP subnet in IP Routing mode.
Defining Static Routes
Routes between the IP interfaces and a default gateway or other router with a WAN connection should
be determined beforehand and entered into the static/default routing table on the DES-3326.
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