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D-Link DES-6500 Layer 3 Stackable Gigabit Ethernet Switch
38
State <
Disabled
>
This drop-down menu allows you to
Enable
or
Disable
STP for the
selected group of ports.
Cost <
0
>
A Port Cost can be set from
1
to
200000000
. The lower the number, the
greater the probability the port will be chosen to forward packets.
Default port cost:
100Mbps port = 200000
Gigabit ports
= 20000
Priority
<0>
A Port Priority can be from
0
to
240
. The lower the number, the greater the
probability the port will be chosen as the Root Port.
Migration
<No>
Select Y
es
or
No
. Choosing Yes will enable the port to migrate from 802.1d
STP status to 802.1w RSTP status. RSTP can coexist with standard STP,
however the benefits of RSTP are not realized on a port where an 802.1d
network connects to an 802.1w enabled network. Migration should be
enabled (yes) on ports connected to network stations or segments that will
be upgraded to 802.1w RSTP on all or some portion of the segment.
Edge
<No>
Select
Yes
or
No.
Choosing Yes designates the port as an edge port. Edge
ports cannot create loops, however an edge port can lose edge port status
if a topology change creates a potential for a loop. An edge port normally
should not receive BPDU packets. If a BPDU packet is received it
automatically loses edge port status. No indicates the port does not have
edge port status.
P2P
<No>
Select
Yes
or
No
. Choosing
Yes
indicates a point-to-point (p2p) shared
link. These are similar to edge ports however they are restricted in that a
p2p port must operate in full duplex. Like edge ports, p2p ports transition to
a forwarding state rapidly thus benefiting from RSTP.
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D-Link DES-6500 Layer 3 Stackable Gigabit Ethernet Switch
39
Configuring Forwarding & Filtering
Static Unicast Forwarding
Open the
Forwarding & Filtering
folder in the
Configuration
menu and click on the
Unicast Forwarding
link.
This will open the
Setup Static Unicast Forwarding Table
, as
shown below.
Figure 4- 12. Static Unicast Forwarding Setup
To add or edit an entry, define the following parameters and then click
Add/Modify
:
Parameter
Description
VLAN ID
The VLAN ID number of the VLAN on which the above Unicast MAC
address resides.
MAC Address
The MAC address to which packets will be statically forwarded.
This must
be a unicast MAC address.
Unit
Allows the designation of the module on which the above MAC address
resides.
Port
Allows the selection of the port number on which the MAC address entered
above resides.
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D-Link DES-6500 Layer 3 Stackable Gigabit Ethernet Switch
40
Static Multicast Forwarding
The following figure and table describe how to set up Multicast forwarding on the switch.
Open the
Forwarding & Filtering
folder and click on the
Multicast Forwarding
link to see
the entry screen below:
Figure 4- 13.
Setup Static Multicast Forwarding Table
The Static Multicast Forwarding Settings page displays all of the entries made into the
switch’s static multicast forwarding table.
Click the
Add
button to open the
Setup Static
Multicast Forwarding Table
, as shown below.
Figure 4- 14.
Setup Static Multicast Forwarding Table
The following parameters can be set:
Parameter
Description
VID
The VLAN ID of the VLAN the above MAC address belongs to.
Multicast MAC
Address
The MAC address of the static source of multicast packets.
This must be a
multicast MAC address.
Port Settings
Allows the selection of ports that will be members of the static multicast
group.
The options are:
None
– no restrictions on the port dynamically joining the multicast group,
Egress
– the port is a static member of the multicast group.
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D-Link DES-6500 Layer 3 Stackable Gigabit Ethernet Switch
41
Configuring VLANs
Understanding IEEE 802.1p Priority
Priority tagging is a function defined by the IEEE 802.1p standard designed to provide a
means of managing traffic on a network where many different types of data may be
transmitted simultaneously. It is intended to alleviate problems associated with the delivery of
time critical data over congested networks. The quality of applications that are dependent on
such time critical data, such as video conferencing, can be severely and adversely affected by
even very small delays in transmission.
Network devices that are in compliance with the IEEE 802.1p standard have the ability to
recognize the priority level of data packets. These devices can also assign a priority label or
tag to packets. Compliant devices can also strip priority tags from packets. This priority tag
determines the packet’s degree of expeditiousness and determines the queue to which it will
be assigned.
Priority tags are given values from 0 to 7 with 0 being assigned to the lowest priority data and
7 assigned to the highest. The highest priority tag 7 is generally only used for data associated
with video or audio applications, which are sensitive to even slight delays, or for data from
specified end users whose data transmissions warrant special consideration.
The Switch allows you to further tailor how priority tagged data packets are handled on your
network. Using queues to manage priority tagged data allows you to specify its relative
priority to suit the needs of your network. There may be circumstances where it would be
advantageous to group two or more differently tagged packets into the same queue. Generally,
however, it is recommended that the highest priority queue, Queue 1, be reserved for data
packets with a priority value of 7. Packets that have not been given any priority value are
placed in Queue 0 and thus given the lowest priority for delivery.
A weighted round robin system is employed on the Switch to determine the rate at which the
queues are emptied of packets. The ratio used for clearing the queues is 4:1. This means that
the highest priority queue, Queue 1, will clear 4 packets for every 1 packet cleared from
Queue 0.
Remember, the priority queue settings on the Switch are for all ports, and all devices
connected to the Switch will be affected. This priority queuing system will be especially
beneficial if your network employs switches with the capability of assigning priority tags.
VLANs
A Virtual Local Area Network (VLAN) is a network topology configured according to a
logical scheme rather than the physical layout. VLANs can be used to combine any collection
of LAN segments into an autonomous user group that appears as a single LAN. VLANs also
logically segment the network into different broadcast domains so that packets are forwarded
only between ports within the VLAN. Typically, a VLAN corresponds to a particular subnet,
although not necessarily.
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D-Link DES-6500 Layer 3 Stackable Gigabit Ethernet Switch
42
VLANs can enhance performance by conserving bandwidth, and improve security by limiting
traffic to specific domains.
A VLAN is a collection of end nodes grouped by logic instead of physical location. End nodes
that frequently communicate with each other are assigned to the same VLAN, regardless of
where they are physically on the network. Logically, a VLAN can be equated to a broadcast
domain, because broadcast packets are forwarded to only members of the VLAN on which the
broadcast was initiated.
Notes About VLANs on the DES-6500
No matter what basis is used to uniquely identify end nodes and assign these nodes VLAN
membership, packets
cannot
cross VLANs without a network device performing a routing
function between the VLANs.
The DES-6500 supports IEEE 802.1Q VLANs. The port untagging function can be used to
remove the 802.1Q tag from packet headers to maintain compatibility with devices that are
tag-unaware.
The Switch’s default is to assign all ports to a single 802.1Q VLAN named “default.”
The “default” VLAN has a VID = 1.
IEEE 802.1Q VLANs
Some relevant terms
:
Tagging
– The act of putting 802.1Q VLAN information into the header of a packet.
Untagging
– The act of stripping 802.1Q VLAN information out of the packet header.
Ingress port
– A port on a switch where packets are flowing into the switch and VLAN
decisions must be made.
Egress port
– A port on a switch where packets are flowing out of the switch, either to
another switch or to an end station, and tagging decisions must be made.
IEEE 802.1Q (tagged) VLANs are implemented on the Switch. 802.1Q VLANs require
tagging, which enables them to span the entire network (assuming all switches on the network
are IEEE 802.1Q-compliant).
VLANs allow a network to be segmented in order to reduce the size of broadcast domains. All
packets entering a VLAN will only be forwarded to the stations (over IEEE 802.1Q enabled
switches) that are members of that VLAN, and this includes broadcast, multicast and unicast
packets from unknown sources.
VLANs can also provide a level of security to your network. IEEE 802.1Q VLANs will only
deliver packets between stations that are members of the VLAN.
Any port can be configured as either
tagging
or
untagging
. The
untagging
feature of IEEE
802.1Q VLANs allows VLANs to work with legacy switches that don’t recognize VLAN tags
in packet headers. The
tagging
feature allows VLANs to span multiple 802.1Q-compliant

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