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.

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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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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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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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