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Ports that have the Edge Port feature enabled continue to transmit BPDUs. The BPDU filtering feature
prevents ports configured as edge ports from sending BPDUs.
If BPDU filtering is configured globally on the switch, the feature is automatically enabled on all operational
ports where the Edge Port feature is enabled. These ports are typically connected to hosts that drop BPDUs.
However, if an operational edge port receives a BPDU, the BPDU filtering feature disables the Edge Port
feature and allows the port to participate in the spanning-tree calculation.
Enabling BPDU filtering on a specific port prevents the port from sending BPDUs and allows the port to
drop any BPDUs it receives.
3.8.4.4.
Root Guard
Enabling root guard on a port ensures that the port does not become a root port or a blocked port. When a
switch is elected as the root bridge, all ports are designated ports unless two or more ports of the root
bridge are connected together. If the switch receives superior STP BPDUs on a root-guard enabled port, the
root guard feature moves this port to a root-inconsistent STP state, which is effectively equal to a listening
state. No traffic is forwarded across this port. In this way, the root guard feature enforces the position of
the root bridge.
When the STP mode is MSTP, the port may be a designated port in one MSTI and an alternate port in the
CIST, etc. Root guard is a per port (not a per port per instance command) configuration, so all the MSTP
instances this port participates in should not be in a root role.
3.8.4.5.
Loop Guard
Loop guard protects a network from forwarding loops induced by BPDU packet loss. The reasons for failing
to receive packets are numerous, including heavy traffic, software problems, incorrect configuration, and
unidirectional link failure. When a non-designated port no longer receives BPDUs, the spanning-tree
algorithm considers that this link is loop free and begins transitioning the link from blocking to forwarding.
Once in forwarding state, the link may create a loop in the network.
Enabling loop guard prevents such accidental loops. When a port is no longer receiving BPDUs and the max
age timer expires, the port is moved to a
loop-inconsistent blocking state
. In the loop-inconsistent blocking
state, traffic is not forwarded so the port behaves as if it is in the blocking state. The port will remain in this
state until it receives a BPDU. It will then transition through the normal spanning tree states based on the
information in the received BPDU.
Note:
Loop Guard should be configured only on non-designated ports. These include ports in alternate or
backup roles. Root ports and designated ports should not have loop guard enabled so that they can forward
traffic
3.8.4.6.
BPDU Protection
When the switch is used as an access layer device, most ports function as edge ports that connect to a
device such as a desktop computer or file server. The port has a single, direct connection and is configured as
an edge port to implement the fast transition to a forwarding state. When the port receives a BPDU packet,
the system sets it to non-edge port and recalculates the spanning tree, which causes network topology
Summary of Contents for QuantaMesh QNOS5
Page 1: ...QuantaMesh Ethernet Switch Configuration Guide QNOS5 NOS Platform ...
Page 209: ...209 Table 7 8 IPv6 Neighbor Discovery Settings ...
Page 226: ...226 Table 8 2 L3 Multicast Defaults ...
Page 254: ...254 Appendix A Term and Acronyms Table 9 5 Terms and Acronyms ...
