Cisco Sg2008 Manual

							Spanning Tree
Configuring STP Interface Settings
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The following information appears in the Designated Root section of the page:
•Bridge ID—The bridge identifier, which is a concatenation of the bridge 
priority and the base MAC address of the bridge.
•Root Bridge ID—The Bridge ID of the root bridge. The bridge with the lowest 
Bridge ID among all the bridges become the root bridge.
•Root Port—The port number that offers the lowest-cost path from this 
bridge to the root bridge. It is significant when the bridge is not the root. The 
default is zero.
•Root Path Cost—The cost of the path from this bridge to the root.
•To p o l o g y  C h a n g e s  C o u n t—The total amount of STP state changes that 
have occurred.
•Last Topology Change—The total amount of time since the last topographic 
change.
STEP  3Click Apply. Your changes are saved to the Running Configuration.
Configuring STP Interface Settings
The STP Inter face Set tings page assigns STP properties to individual ports or 
LAGs. These settings are applicable to both the Classic STP and Rapid STP. 
To edit settings for a port or LAG:
STEP 1Click Spanning Tree > STP Interface Settings in the navigation window.
The STP Interface Settings Table displays configuration information for each port 
and LAG. By default, all ports are enabled for STP operation. 
NOTE: The list ports/LAGs might span more than one page. Use the Page list to 
display the next set of entries.
STEP  2Select the port or LAG to configure and click Edit.
STEP  3Enter the parameters: 
						

							Spanning Tree
Configuring STP Interface Settings
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•STP—Select to enable STP operation on the port/LAG.
•Auto Edge—Select Enable to allow the switch to automatically determine if 
the port is an edge port or PortFast. A port is an edge port if it is not 
connected to a bridge. Auto-detection speeds up the transition of the port to 
forwarding state. A port can forward traffic and learn MAC addresses when 
it is in forwarding state.
•Edge Port—Select Enable to manually configure the port as an edge port. 
•BPDU Handling—Bridge Protocol Data Units (BPDUs) are the messages 
exchanged between switches to calculate STP topology. Select the method 
of BPDU packet handling when the spanning tree is disabled on an inter face :
-Filtering—Enables the port to discard BPDUs received on interfaces 
that are not enabled for STP.
-Flooding—Allows flooding of BPDUs received on non-spanning-tree 
ports to all other non-spanning-tree ports.
•Path Cost—Specify the port path cost. The cost of a path to the root bridge 
is the sum of the costs of all ports in the path. The path cost is used by CST 
and RSTP to forward traffic when a path is being rerouted. Select Use 
Default to set the path cost to the port speed. Or select User Defined to set 
a custom value between 0 and 200,000,000. A value of zero means the path 
cost is set according to the ports speed.
STEP  4Click Apply and then click Close. Your changes are saved to the Running 
Configuration.
The new configuration appears in the STP Interface Settings Table along with the 
following information about the port/LAG.
•Operational Edge Status—Indicates if a port is currently operating as an 
edge port (or PortFast port). This will indicate Enabled if the port is in the 
forwarding state due to either of the following configurations:
-The port is configured as an Edge Port and is therefore automatically in 
the forwarding state.
-The port is configured as an Auto Edge port and, because it has not 
received BDPUs, has transitioned to forwarding state. 
						

							Spanning Tree
RSTP Interface Settings
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•Port State—Current STP state of a port. If enabled, the port state 
determines the forwarding action that is taken on traffic. Possible port states 
are: 
-Disabled—STP is currently disabled on the port. The port does not 
participate in the spanning tree, but is in an operational state to learn 
MAC addresses and forward traffic.
-Discarding—Port is currently blocked and cannot be used to forward 
traffic or learn MAC addresses.
-Learning—Port is currently in the learning mode. The port cannot 
forward traffic, however, it can learn new MAC addresses.
-Forwarding—Port is currently in the forwarding mode. The port can 
forward traffic and learn new MAC addresses.
•Designated Bridge ID—Bridge identifier of the bridge that offers the 
lowest root path cost to a LAN. The ID is a concatenation of the bridge 
priority and the base MAC address of the bridge.
•Designated Port ID—Port identifier on the Designated Bridge that offers 
the lowest root path cost to the LAN. The ID is a concatenation of the port 
priority and the interface number of the port.
•Designated Cost—The root path cost from the designated bridge to the 
root bridge. Ports with lower designated cost are less likely to be blocked 
when STP detects loops.
•Speed—Port speed.
•LAG—LAG that the port is a member of, if any.
RSTP Interface Settings
Rapid Spanning Tree Protocol (RSTP) ensures a faster convergence of a loop-free 
spanning tree for any bridged LAN. To display the RSTP Interface Settings page, 
click Spanning Tree > RSTP Interface Settings in the navigation window.
A rapid spanning tree topology is formed automatically when RSTP is selected as 
the spanning tree mode. Use the STP Status & Global Settings page to enable 
RSTP mode. 
						

							Spanning Tree
RSTP Interface Settings
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By default, the RSTP Interface Settings Table displays information for each port. 
Use the Interface Type list to display ports or LAGs in the table. The RSTP 
Interface Table displays the following information for each port:
•Point to Point Operational Status—A physical port has a point-to-point 
connection to a LAN if it operates in full duplex. 
•Port Role—Port role assigned by the STP algorithm to provide to STP paths. 
The possible field values are:
-Root—Provides the lowest root path cost to the root bridge among all 
the ports in the switch.
-Designated—Provides the lowest root path cost to the root bridge from 
a LAN. The switch is the designated bridge in the LAN.
-Alternate—Provides an alternate path to the root bridge from the root 
interface.
-Backup—Provides a backup path to the designated port path toward 
the Spanning Tree leaves. Backup ports occur only when two ports are 
connected in a loop by a point-to-point link, or when a LAN has two or 
more connections connected to a shared segment.
-Disabled—The port is not participating in the Spanning Tree.
•Mode—Indicates whether the RSTP administrative mode is enabled or 
disabled for the port.
•Edge Port Operational Status—If enabled for the port or LAG, the port is 
automatically placed in the forwarding state. See Configuring STP 
Interface Settings for instructions on modifying this setting.
•Port Status—The operational state of the port.
You can select a port and click Activate Protocol Migration to have the switch 
send RSTP BPDUs to the port . This can be used to test whether all legacy bridges 
on the LAN have been removed. 
						

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RSTP Interface Settings
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MSTP Instance Settings
MSTP Interface Settings 
						

							Spanning Tree
RSTP Interface Settings
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							7
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MAC Address Tables
This chapter describes the static configuration and dynamic learning of Media 
Access Control (MAC) addresses into the filtering database of the switch. The 
switch searches its filtering database to determine which port a packet is to be 
forwarded to. The filtering database is also referred as the bridging table in this 
document. The search is based on the VLAN and destination MAC address of the 
packet. If search does not result with a matching entry, the switch floods the 
packets to the VLAN excluding the ingress port. 
It includes the following topics:
•Configuring Static MAC Addresses
•Configuring the Aging Time for Dynamic Addresses
•Dynamic MAC Addresses
Configuring Static MAC Addresses
The Static Addresses page displays a list of MAC addresses that are manually 
configured into the bridging table of the switch. A static MAC address is also 
associated with a VLAN and a port.
To add static MAC address entries:
STEP 1Click MAC Address Tables > Static Addresses in the navigation window.
STEP  2Click Add.
STEP 3 Enter the parameters:
•VLAN ID—Select the VLAN in which the device with the static MAC address 
resides.
•Interface—Specify the port/LAG in which the device with the static MAC 
addresses can be reached. 
						

							MAC Address Tables
Configuring Static MAC Addresses
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•MAC Address— Enter the static MAC address.
•Status—Select a status for this static MAC address:
-Permanent—When this status is selected, the static MAC address does 
not expire. Note, however, that if the switch is rebooted, the entry is not 
restored unless the Running Configuration file type was copied to the 
Startup Configuration file type. See Copying and Saving Configuration 
Files.
-Delete on Timeout—When this status is selected, the static MAC 
address is static but may expire due to inactivity. In this respect, it is 
treated like a dynamically learned MAC address. See the Dynamic 
Address Settings to set the aging period.
-Secure—When this status is selected, the MAC address is secured and 
is used in conjunction with the Port Security feature. When a MAC 
address is secured at a port, packets that originate from the MAC 
address can only be ingressed from the secured port. Otherwise, the 
packets are discarded. If port security is disabled on the port, the MAC 
address is deleted from the static MAC address list. When Port Security 
is enabled at a port, the port can support a maximum of 256 static and 
dynamic MAC addresses. (For more information, see Enabling Port 
Security). 
STEP  4Click Apply and then click Close. Your changes are saved to the Running 
Configuration.
NOTETo delete a static MAC address, select it in the table and click Delete. 
						

							MAC Address Tables
Configuring the Aging Time for Dynamic Addresses
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Configuring the Aging Time for Dynamic Addresses
The Dynamic Address Settings page enables you to set an aging time, after 
which the system removes addresses in the dynamic MAC address table that 
have not been refreshed. The aging period applies to dynamically learned 
addresses and to static addresses that are configured to Delete on Timeout. The 
default aging time is 300 seconds.
To configure the aging time:
STEP 1Click MAC Address Tables > Dynamic Address Settings in the navigation 
window.
STEP  2Specify an aging time from 10 to 1,000,000 seconds.
STEP  3Click Apply. Your changes are saved to the Running Configuration.
Dynamic MAC Addresses
When the switch cannot find an entry in its bridging table that matches the VLAN 
and the destination MAC address of an incoming packet, the switch learns the 
MAC address, the VLAN, and the ingress port of the packet and adds an entry to 
the Dynamic Address table.
To prevent the bridging table from overflowing and to make room for new 
addresses, an address is deleted from the bridging table if no traffic is received 
from a dynamic MAC address for the configured aging period (see Configuring 
the Aging Time for Dynamic Addresses).
To display the Dynamic Addresses page, click MAC Address Tables > 
Dynamic Addresses in the navigation window.
NOTEThis page might take up to 45 seconds to display when the Dynamic Address Table 
contains the maximum number of entries.
By default, the Dynamic Address Table displays all dynamically learned MAC 
addresses. You can enter filter criteria and click Go to filter the display. Use the 
VL AN ID filter to display table entries for a particular VLAN. Use the MAC Address 
filter to display entries for a particular MAC address. Use the Inter face filter to 
display entries for a particular port or LAG. Click Clear Filter to display all of the 
entries. 
						

							MAC Address Tables
Dynamic MAC Addresses
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The Dynamic Address Table displays the following fields for each entry it learns:
•VLAN ID—VLAN on which the MAC address was learned. Frames are 
forwarded to the interface only if they are associated with this VLAN.
•MAC Address—The dynamically learned MAC address.
•Interface—The port on which the MAC address was dynamically learned. 
Frames specifying this MAC address and VLAN as the destination are 
forwarded out to this port. 
Click Clear Table to clear all dynamic MAC address entries from the table.