Convergence - Juniper EX9200 Features Manual

Table 17: Selecting a Spanning-Tree Protocol (continued)
Protocol Advantages
MSTP Multiple Spanning Tree Protocol works with most
VLANs.
RSTP and STP are recognized as distinct Spanning
Tree regions by MSTP.
VSTP VLAN Spanning Tree Protocol works with VLANs
that require device compatibility.
VSTP and RSTP are the only spanning-tree
protocols that can be configured concurrently on a
switch.
Related
Documentation
Configuring a Spanning-Tree Instance Interface as an Edge Port for Faster Convergence
Related
Documentation
Copyright © 2017, Juniper Networks, Inc.
Understanding STP for EX Series Switches
Understanding RSTP for EX Series and QFX Series Switches on page 3
Understanding MSTP for EX Series and QFX Series Switches on page 78
Configuring VLAN Spanning Tree Protocol on page 168
RSTP, MSTP, and VSTP instance interfaces configured as edge ports enable the protocol
to converge faster than the original IEEE 802.1D STP version. Edge ports transition directly
to the forwarding state, and so the protocol does not need to wait for BPDUs to be
received on edge ports.
The Junos OS supports automatic detection of edge ports as described in the RSTP
standard. Layer 2 bridges do not expect to receive BPDUs for edge ports. If a BPDU is
received for an edge port, the port becomes a non-edge port.
Keep the following guidelines in mind when configuring spanning-tree instance interfaces
as edge ports:
Do not configure a spanning-tree instance interface as an edge port if it is connected
to any Layer 2 bridge. An instance interface connected to Layer 2 bridges but configured
as an edge port can cause physical loops.
if the spanning-tree protocol is configured to run the original IEEE 802.1D spanning-tree
version, the edge-port option (if configured) is ignored.
If edge ports are configured at both the VSTP global and VLAN levels, the configuration
at the VLAN level overrides the global configuration.
Example: Configuring BPDU Protection on Edge Interfaces to Prevent STP Miscalculations
Configuring Rapid Spanning Tree Protocol
Disadvantages
Some protocols require compatibility that is not
provided by MSTP. In this case, use VSTP.
MSTP supports a limited number of ports.
MSTP uses more CPU than RSTP and does not
converge as fast as RSTP.
With VSTP there can be only STP instance per
VLAN, whereas MSTP lets you combine multiple
VLANs in one instance.
VSTP supports a limited number of ports compared
to RSTP.
VSTP uses more CPU than RSTP and does not
converge as fast as RSTP.
Chapter 7: Using VSTP
161