Specifications

Terms and Definitions
March 14, 2011 Page 28 of 29
FID Filter Identifier. Each VLAN is associated to a FID. VLANs are mapped to SIDs using
their FID association.
Forward delay Time interval (in seconds) the bridge spends in listening or learning mode before it
begins forwarding BPDUs.
Hello time Time interval (in seconds) at which the bridge sends BPDUs.
ISLs Inter-Switch Links.
Loop Protect Prevents or short circuits loop formation in a network with redundant paths by
requiring ports to receive type 2 BPDUs (RSTP/MSTP) on point-to-point inter-switch
links (ISLs) before their states are allowed to become forwarding.
Master port The MSTI port whose connecting CIST port is root port for an entire MST region.
Max age Maximum time (in seconds) the bridge can wait without receiving a configuration
message (bridge “hello”) before attempting to reconfigure.
MST region An MSTP group of devices configured together to form a logical region. The MST
region presents itself to the rest of the network as a single device, which simplifies
administration.
MSTI Multiple Spanning Tree Instance. N-Series, S-Series, stackable, and standalone
switch devices support up to 64 MSTIs.
Path cost Sum of the port costs in the best path to the root bridge.
Port cost Value assigned to a port based on the speed of the port. The faster the speed, the
lower the cost. This helps to determine the quickest path between the root bridge
and a specified destination. The segment attached to the root bridge normally has a
path cost of zero.
Port priority Assigns a port’s priority in relation to the other ports on the same bridge.
Root bridge Logical center of the Spanning Tree, used by STP to determine which paths to block
and which to open.
Root port Port in an active topology through which the root bridge can be reached.
SID Spanning tree identifier. By default, SID 0 is assumed. VLANs are mapped to SIDs
using their FID association.
SpanGuard Prevents Spanning Tree respans that can occur when BPDUs are received on user
ports and notifies network management that they were attempted.
Table 9 Spanning Tree Terms and Definitions (continued)
Term Definition