Allied Telesis RAPIER I, X900-48FE manual Introduction to Ethernet Protection Switching Ring Epsr

2 Software Reference

Introduction to Ethernet Protection

Switching Ring (EPSR)

Ethernet Protection Switching Ring (EPSR) is a protection system employed to prevent loops within Ethernet ring based topologies. EPSR offers a rapid detection and recovery time (in the order of 50 ms, depending on configuration) if a link or node fails. This rapid recovery time makes EPSR a more effective alternative to spanning tree based options when using ring based topologies to create high speed resilient layer two networks.

Ring Components and Operation

EPSR operates only on ring based topologies. An EPSR ring comprises a series of nodes (Ethernet bridges) connected end to end. Figure 1-1shows a basic ring configuration. A ring comprises one master node and a number of transit nodes. Each node connects to the ring via two ports. On the master node one port is configured to be the primary port and the other, the secondary port.

Figure 1-1: Simple EPSR ring configuration

End User Ports

Control VLAN “forwarding”

Data VLAN“blocked”

Control VLAN “forwarding” Data VLAN “forwarding”

End User Ports

S P

Master

Node

Transit

Node

4

C
on
tr
		ol
D			VL
	at			A
					N
		a
			VL
				A
D					N
						_
	at						1
		a		V
				L
					A
					N
						_
							2
Transit								End User Ports
Node
			1

	Transit	Transit
End User Ports	Node
		Node
	3
		2

Control VLAN
	Control VLAN
Data VLAN_1		Primary Port	P
	Data VLAN_1
Data VLAN_2		Secondary Port	S
	Data VLAN_2

End User Ports

EPSR 1.eps

EPSR Instances and Domains

Each physical EPSR ring contains one or more EPSR instances. An EPSR instance can be thought of as a component of an EPSR ring existing on a single node. A set of instances across the whole ring is called a “domain.” Therefore a ring whose individual nodes each have two instances, will result in a two domain ring. Each instance contains a control VLAN and a number of data VLANs. EPSR instances are created using the create epsr command on

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