Cisco Catalyst 3560-X User Manual

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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring STP
Understanding Spanning-Tree Features
Disabled State
A Layer 2 interface in the disabled state does not participate in frame forwarding or in the spanning tree.
An interface in the disabled state is nonoperational.
A disabled interface performs these functions:
• Discards frames received on the interface
• Discards frames switched from another interface for forwarding
• Does not learn addresses
• Does not receive BPDUs
How a Switch or Port Becomes the Root Switch or Root Port
If all switches in a network are enabled with default spanning-tree settings, the switch with the lowest
MAC address becomes the root switch. In Figure 1-3, Switch A is elected as the root switch because the
switch priority of all the switches is set to the default (32768) and Switch A has the lowest MAC address.
However, because of traffic patterns, number of forwarding interfaces, or link types, Switch A might not
be the ideal root switch. By increasing the priority (lowering the numerical value) of the ideal switch so
that it becomes the root switch, you force a spanning-tree recalculation to form a new topology with the
ideal switch as the root.
Figure 1-3 Spanning-Tree Topology
When the spanning-tree topology is calculated based on default parameters, the path between source and
destination end stations in a switched network might not be ideal. For instance, connecting higher-speed
links to an interface that has a higher number than the root port can cause a root-port change. The goal
is to make the fastest link the root port.
For example, assume that one port on Switch B is a Gigabit Ethernet link and that another port on
Switch B (a 10/100 link) is the root port. Network traffic might be more efficient over the Gigabit
Ethernet link. By changing the spanning-tree port priority on the Gigabit Ethernet port to a higher
priority (lower numerical value) than the root port, the Gigabit Ethernet port becomes the new root port.
86475
DP
DP
RP
DP
RP
DP
RP = Root Port
DP = Designated Port
DP
RP
DA
CB

Cisco Catalyst 3560-X Specifications

General

Enclosure Type	Rack-mountable - 1U
Subtype	Gigabit Ethernet
Ports	48 x 10/100/1000 + 4 x SFP
Flash Memory	64 MB
Power Device	Internal power supply
Voltage Required	AC 120/230 V (50/60 Hz)
Operating System	Cisco IOS
Device Type	Switch
Performance	Switching capacity: 128 Gbps
Jumbo Frame Support	Yes
Routing Protocol	RIP-1, RIP-2, EIGRP
Remote Management Protocol	SNMP 1, RMON 1, RMON 2, RMON 3, RMON 9, Telnet, SNMP 3, HTTP, HTTPS
Features	DHCP support, VLAN support, QoS, IPv6 support, Syslog
Compliant Standards	IEEE 802.3, IEEE 802.3u, IEEE 802.3z, IEEE 802.1D, IEEE 802.1Q, IEEE 802.3ab, IEEE 802.1p, IEEE 802.3af, IEEE 802.3x, IEEE 802.3ad, IEEE 802.1w, IEEE 802.1x, IEEE 802.1s, IEEE 802.3ah, IEEE 802.1ag, IEEE 802.3at
Stacking	Stackable
Security Features	SSH, RADIUS, TACACS+
Management	CLI
Dimensions (H x W x D)	17.5 in
Operating Temperature	32 to 113 °F (0 to 45 °C)
Humidity	10 - 95% (non-condensing)