iES26GF
User’s
Manual
UM-iES26GF-1.2.3-EN.docx
Pages 18 of 169
4.3
STP/RSTP/MSTP
STP/RSTP Introduction
STP (Spanning Tree Protocol), its advanced versions RSTP (Rapid Spanning Tree Protocol) and
MSTP (Multiple Spanning Tree Protocol), are designed to prevent network loops and provide network
redundancy. Network loops occur frequently in large networks when two or more paths run to the
same destination, broadcast packets could get in to an infinite loop and cause congestion in the network.
STP can identify the best path to the destination and block all other paths. The blocked links will stay
connected but inactive. When the best path fails, the blocked links will be activated. Compared to
STP which recovers a link in 30 to 50 seconds, RSTP can shorten the time to 5 to 6 seconds.
For details on RSTP, see Section 5.4.4 RSTP.
MSTP Introduction
MSTP was developed to improve recovery times since STP and RSTP takes seconds, which is not
acceptable in some industrial applications. MSTP supports multiple spanning trees within a
network by grouping and mapping multiple
VLAN’s
into different spanning-tree instances,
known as
MSTI’s,
forming individual MST regions. Each switch is assigned an MST region. Each
MST region consists of one or more MSTP switches with the same
VLAN’s,
at least one MST
instance, and the same MST region name. This allows the switches to use different paths in the
network to effectively balance loads.
4.4
MRP Introduction
MRP (Media Redundancy Protocol) is an industry standard for high-availability Ethernet networks.
MRP allows Ethernet switches in ring configuration to recover from failure rapidly to ensure seamless
data transmission. A MRP ring (IEC 62439) can support up to 50 devices and will enable a back -up
link in 80ms (adjustable to max. 200ms/500ms).
4.5
Fast Recovery Introduction
Fast recovery mode can be set to connect multiple ports to one or more switches providing
redundant links. Fast recovery mode supports 12 priorities. Only the first priority will be active port,
the other ports with different priorities will be backup ports.
For details on Fast Recovery, see Section 5.4.6 Fast Recovery.
