Cisco Catalyst 3560-X User Manual

1-9
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring Optional Spanning-Tree Features
Understanding Optional Spanning-Tree Features
If link L1 fails as shown in Figure 1-7, Switch C cannot detect this failure because it is not connected
directly to link L1. However, because Switch B is directly connected to the root switch over L1, it detects
the failure, elects itself the root, and begins sending BPDUs to Switch C, identifying itself as the root.
When Switch C receives the inferior BPDUs from Switch B, Switch C assumes that an indirect failure
has occurred. At that point, BackboneFast allows the blocked interface on Switch C to move
immediately to the listening state without waiting for the maximum aging time for the interface to expire.
BackboneFast then transitions the Layer 2 interface on Switch C to the forwarding state, providing a path
from Switch B to Switch A. The root-switch election
takes approximately 30 seconds, twice the Forward
Delay time if the default Forward Delay time of 15 seconds is set. Figure 1-7 shows how BackboneFast
reconfigures the topology to account for the failure of link L1.
Figure 1-7 BackboneFast Example After Indirect Link Failure
If a new switch is introduced into a shared-medium topology as shown in Figure 1-8, BackboneFast is
not activated because the inferior BPDUs did not come from the recognized designated switch
(Switch B). The new switch begins sending inferior BPDUs that indicate it is the root switch. However,
the other switches ignore these inferior BPDUs, and the new switch learns that Switch B is the
designated switch to Switch A, the root switch.
Figure 1-8 Adding a Switch in a Shared-Medium Topology
L1
L2 L3
Switch C
Switch A
(Root)
Switch B
Link failure
44964
BackboneFast changes port
through listening and learning
states to forwarding state.
Switch A
(Root)
Switch C
Switch B
(Designated bridge)
Added switch
44965
Blocked port

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)