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STP

The Rapid Spanning Tree Protocol (RSTP) provides rapid convergence of the spanning tree by

assigning port roles and by determining the active topology. The RSTP builds upon the

IEEE 802.1D STP protocol to select the switch with the highest switch priority as the root switch.

Reconfiguration of the spanning tree can occur in less than 1 second.

Basic—RSTP Configuration

The Basic RSTP Configuration screen lets you enable RSTP:

1.

Select Switching > STP > Basic > RSTP Configuration. A screen similar to the following

displays.

2.

Select a radio button to enable or disable RSTP:

•

Disable

. RSTP is disabled. This is the default setting.

•

Enable

. RSTP is enabled.

3.

Click

Apply

to confirm any settings changes.

Advanced—RSTP Configuration

In addition to the function of the Basic RSTP Configuration screen, The Advanced RSTP

Configuration screen lets you view and modify the bridge settings:

1.

Select Switching > STP > Advanced > RSTP Configuration. A screen similar to the following

displays.

Figure 4-14

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2.

Under Bridge Settings, view or modify the bridge settings. The following configurable fields

are displayed with their possible ranges and default values:

•

Bridge Priority

.

Specifies the priority of the current bridge. After exchanging bridge

protocol data units (BPDUs) with other STP-enabled devices, the device with the lowest

priority value becomes the root bridge.

•

Bridge Max Age

. Specifies the maximum age of the current bridge in seconds. This is the

maximum age of the STP information that is learned from the network before it is

discarded.

•

Bridge Hello Time

.

Specifies the period in seconds that the switch waits before sending

configuration PDUs when it is the root of the spanning tree or trying to become the root.

•

Bridge Forward Delay

.

Indicates the period in seconds that the port stays in each of the

listening and learning states that precedes the forward state. This period is also used to age

all dynamic entries in the forwarding databases when a topology change has been detected

and is underway.

3.

Click

Apply

to confirm any settings changes.

Advanced—Port Configuration

The Port Configuration screen, also referred to as the Rapid Spanning Tree Port Configuration

screen, lets you view and modify the RSTP settings:

1.

Select Switching > STP > Advanced > Port Configuration. A screen similar to the following

displays.

Figure 4-15

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2.

You can make changes to the RSTP port settings for an individual port, for a group of ports, or

for all ports simultaneously:

•

To change the RSTP port settings for an individual port, select the check box to the left of

its port number, and then select the RSTP port settings.

•

To change the RSTP port settings for a group of ports, select the check boxes to the left of

their port numbers, and then select the RSTP port settings.

•

To change the RSTP port settings for all ports simultaneously, select the check box at the

top of the column of check boxes, and then select the RSTP port settings.

Figure 4-16

Note:

You can also enter the interface number (that is, the port number) in the

GO

TO INTERFACE

field, and then click

GO

.

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The following RSTP port information is displayed. Except for the Interface and State fields,

all fields are configurable:

•

Interface

. Shows the port number.

•

Path Cost

. Specifies the cost of the port. Cost means the contribution of this port to the

cost of paths toward the spanning tree root that include this port. The switch uses this

value to determine which port is the forwarding port. If all other factors are equal, the path

with the lowest cost to the root bridge is the active path. The possible values are between 1

and 65535.

•

Priority

. Specifies the priority of the port. This is the value of the priority field contained

in the first octet of the port ID. The port with the lowest number has the highest priority.

The possible values are 0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224,

and 240.

•

Edge

.

Specifies whether the port is the edge port. Once configured as an edge port, the

port immediately transitions to the forwarding state. The possible values are:

–

Yes

. Specifies that the port is the edge port.

–

No

. Specifies that the port is not the edge port.

•

P2P Force

.

Specifies whether the port is a point-to-point link. If you connect a port to

another port though a point-to-point link and the local port becomes a designated port, it

negotiates a rapid transition with the other port to ensure a loop-free topology. The

possible values are:

–

Yes

. Specifies that the port is a point-to-point link.

–

No

. Specifies that the port is not a point-to-point link.

•

State

. Shows the RSTP port status.

3.

Click

Apply

to confirm any settings changes.

Multicast

You can configure IGMP snooping, static multicasting, and multicast group membership.

IGMP Snooping

IGMP specifies how a host can register to a router to receive specific multicast traffic. Configure

the switch to use IGMP snooping in subnets that receive IGMP queries from either IGMP or the

IGMP snooping querier. IGMP snooping constrains multicast traffic at Layer 2 by configuring

Layer 2 LAN ports dynamically to forward multicast traffic only to those ports that want to receive

it. IGMP is a standard defined in RFC1112 for IGMPv1 and in RFC2236 for IGMPv2.

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To configure IGMP snooping:

1.

Select Switching > Multicast > IGMP Snooping. A screen similar to the following displays.

.

2.

Select a radio button to enable or disable IGMP snooping:

•

Disable

. IGMP snooping is disabled. This is the default setting.

•

Enable

. IGMP snooping is enabled.

When you enable IGMP snooping, the screen expands to display fields in which you can

specify how IGMP leave packets are processed. See

step 4

.

3.

Select a radio button to enable or disable blocking of unknown multicast addresses:

•

Disable

. Blocking of unknown multicast addresses is disabled. This is the default setting.

•

Enable

. Blocking of unknown multicast addresses is enabled.

4.

When you enable IGMP snooping, the screen expands to display fields in which you can

specify how IGMP leave packets are processed. In addition, dynamic multicast information is

displayed. Select a radio button to specify how IGMP leave packets are processed:

•

Disable

. Specifies that an incoming IGMP leave packet is forwarded to the multicast

router, that is, the incoming IGMP leave packet is not blocked. When the multicast router

receives the packet, it closes the channel.

•

Enable

. Specifies that an incoming IGMP leave packet is filtered (also referred to as

blocked) and, therefore, not forwarded to the multicast router.This is the default setting.

Under Dynamic Multicast, the following information is displayed:

•

ID

. Shows the dynamic multicast entry ID.

•

VID

. Shows the VLAN ID.

Figure 4-17