About Backbonefast - Cisco Catalyst 4500 Series Configuration Manual

Chapter 23 Configuring Optional STP Features
Station update rate set to 150 packets/sec.
UplinkFast statistics
-----------------------
Number of transitions via uplinkFast (all VLANs)
Number of proxy multicast addresses transmitted (all VLANs) :5308
Name
-------------------- ------------------------------------
VLAN1
VLAN2
VLAN3
VLAN4
VLAN5
VLAN6
VLAN7
VLAN8
VLAN10
VLAN15
VLAN1002
VLAN1003
VLAN1004
VLAN1005
Switch#

About BackboneFast

BackboneFast is a complementary technology to UplinkFast. UplinkFast is designed to quickly respond
to failures on links directly connected to leaf-node switches, but it does not help with indirect failures in
the backbone core. BackboneFast optimizes the topology based on the Max Age setting. It allows the
default convergence time for indirect failures to be reduced from 50 seconds to 30 seconds. However, it
never eliminates forward delays and offers no assistance for direct failures.
BackboneFast should be enabled on every switch in your network.
Note
Sometimes a switch receives a BPDU from a designated switch that identifies the root bridge and the
designated bridge as the same switch. Because this should not happen, the BPDU is considered inferior.
BPDUs are considered inferior when a link from the designated switch has lost its link to the root bridge.
The designated switch transmits the BPDUs with the information that it is now the root bridge as well
as the designated bridge. The receiving switch ignores the inferior BPDU for the time defined by the
Max Age setting.
After receiving inferior BPDUs, the receiving switch tries to determine if there is an alternate path to the
root bridge.
•
•
OL-25340-01
Interface List
Fa6/9(fwd), Gi5/7
Gi5/7(fwd)
Gi5/7(fwd)
Gi5/7(fwd)
Gi5/7(fwd)
Gi5/7(fwd)
Gi5/7(fwd)
If the port that the inferior BPDUs are received on is already in blocking mode, then the root port
and other blocked ports on the switch become alternate paths to the root bridge.
If the inferior BPDUs are received on a root port, then all presently blocking ports become the
alternate paths to the root bridge. Also, if the inferior BPDUs are received on a root port and no other
blocking ports exist on the switch, the receiving switch assumes that the link to the root bridge is
down and the time defined by the Max Age setting expires, which turns the switch into the root
switch.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
About BackboneFast
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