Introduction EPSR Introduction
Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
4-114
4.6 Ethernet Protection Switched Ring (EPSR) and
SuperLoop Prevention
4.6.1 EPSR Introduction
Ethernet Protection Switched Ring (EPSR) is a protection scheme for Ethernet networks, specifically for ring-
based network topologies. EPSR provides a 50 milliseconds switching time for an Ethernet-based ring network,
similar to that provided by the Synchronous Optical Network (SONET) protocol, to maintain layer 2 redun-
dancy in the network.
EPSR assists the multicast streams in being redirected around a faulty link in a ring network fast enough to
result in an uninterrupted multicast service. The EPSR protocol provides fast protection switching to layer 2
switches which are interconnected in an Ethernet ring topology.
Note: EPSR is only supported on ring topology networks.
EPSR is available only on ring topology networks comprised of nodes that are physically connected to form a
ring. Each node on the ring will have two Ethernet ports connected to the ring. EPSR operates over these
Ethernet ports.
4.6.2 Overview of EPSR Configuration
The protection scheme for an Ethernet ring network basically operates by configuring an EPSR domain on the
ring. The vlans that require fault protection are configured on all the ring ports and are assigned to the above
mentioned EPSR domain. All such vlans are referred to as the protected vlans. Additionally, a control vlan is
assigned to the EPSR domain and is used to send and receive the EPSR protocol control messages over the ring
network that are then used accordingly by all the nodes to prevent loops in the network and ensure that none
of the nodes are isolated from the network.
Note: There can only be one control vlan per EPSR domain and is configured to use tagged frames. This
control vlan is unique to this domain and cannot be re-used for another domain. Also, the control vlan
must be provisioned to have the highest priority p-bit setting (as per IEEE 802.1p) and to be mapped
to the highest priority queue in the system.
One of the nodes in the ring is designated as the MASTER node while all the other nodes are designated as
TRANSIT nodes. For example, in the figures accompanying this text, Allied Telesis System C is designated the
master node while all the other systems are designated transit nodes. One ring port on the master node is des-
ignated to be the Primary Port (PP) and the other ring port is designated to be the Secondary Port (SP).
Note: The initial description of the EPSR configuration uses a standard (rather than UFO) VLAN so that the
Master Node can be any node. When UFO VLANs are configured, the Master Node must be the
upstream node.
When the ring is operating normally, the master node blocks its SP port for all non-control traffic (data carried
over the protected vlans) belonging to the EPSR domain, preventing a loop on the ring. The layer 2 Ethernet
switching and learning mechanisms operate normally on each of the nodes in the ring. However, the control
To Next Page
Loading...
