Allied Telesis AT-8700XL, RAPIER I, X900-48FE, AT-8900, AT-9900 Epsr and Spanning Tree Operation

Ethernet Protection Switching Ring (EPSR) 13

EPSR and Spanning Tree Operation

EPSR and the Spanning Tree protocols (STP) each address the issue of data loop prevention, although their method of doing so is quite different. For information on STP, see the Spanning Tree Chapter of your switch’s Software Refernce. EPSR is manually configured to explicitly identify which link(s) will be broken in the defined ring, whereas STP/RSTP calculates where to break links based upon user provisioned values (metrics) that are compared to determine the "best" (or lowest cost) paths for data traffic.

At the practical level these two techniques can be employed to create complementary hybrid EPSR / STP configurations. Such a configuration might have a high speed fibre loop topology backbone—controlled and managed using EPSR. Lobes could extend out from each loop node into a user mesh network. Any loops existing within this mesh network would be controlled and managed using STP/RSTP. Figure 1-9 on page 1-13shows a basic combined EPSR / STP network.

Figure 1-9: EPSR and Spanning Tree Operation

Port 2

Other

Port 1

Secondary

Ports

Primary

S

P

C

N

A

o

n

L

t

V

r

Node 1

o

l

l

o

V

r

L

t

o

n

A

C

Master

N

N

D

a

L

A

Node

t

V

a

a

V

L

A

t

N

a

D

Other

Transit

EPSR Ring

Transit

Other

Ports

Node

Node

Ports

Node 2

Node 4

Port 1

Transit

Port 2

Node

Port 4

Node 3

Port 3

VLA

N

Data

Data

STP/RSTP

V

Port 1

LAN

Port 1

Network

Other

Data VLAN

Other

Ports

Ports

Port 2

Port 2

Control VLAN (control_ring)

Data VLAN

EPSR 5.eps

Note that EPSR and STP cannot share the same ports.