Overview Of Stp, Rstp, And Mstp; Figure 8-1 Defect Of Rstp - Huawei Quidway S9300 Configuration Manual

8 MSTP Configuration

8.1 Overview of STP, RSTP, and MSTP

This section describes the concepts of STP, RSTP, and MSTP.
STP and RSTP
l
l

Figure 8-1 Defect of RSTP

Host C
(VLAN3)
Host B
(VLAN2)
8-2
STP
The IEEE 802.1D standard issued in 1998 defines STP.
STP is a management protocol on the data link layer and is used to detect and prevent loops
on the local area network (LAN). STP blocks redundant links and trims a network into a
tree topology to prevent loops.
However, an STP network converges slowly. A port, even an edge port, transits to the
forwarding state after at least 30 seconds.
RSTP
The IEEE 802.1W standard issued in 2001 defines the RSTP.
As an enhancement of STP, RSTP speeds up network convergence.
However, both RSTP and STP have a defect, that is, all the VLANs on the same LAN share
the same spanning tree. As a result, load balancing cannot be implemented among VLANs,
and packets of some VLANs may fail to be forwarded.
As shown in Figure 8-1, RSTP is applied to the LAN. The structure of the spanning tree
is represented by dotted lines and S9300F is the root switch. The link between S9300B and
S9300E and the link between S9300A and S9300D are blocked. Links of VLAN 2 and
VLAN 3 permit packets from the two VLANs to pass through. Other links do not permit
packets from VLAN 2 and VLAN 3 to pass through.
S9300A
VLAN3
VLAN3
S9300B
VLAN2
VLAN3
VLAN2
S9300C
spanning tree ( root switch: S9300F)
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Copyright © Huawei Technologies Co., Ltd.
Quidway S9300 Terabit Routing Switch
S9300D
VLAN2
VLAN2
VLAN2
VLAN3
VLAN3
S9300F
Configuration Guide - Ethernet
VLAN2
Host A
(VLAN2)
S9300E
Host D
(VLAN3)
VLAN3
Issue 03 (2009-08-20)