Table of Contents
Advertisement
ERP Overview
•
Refer to the
"ERP Specifications" on page 9-2
Guard Timer. When the failed link recovers, a ring node starts the Guard Timer. The Guard Timer is used
to prevent the ring nodes from receiving outdated R-APS messages that are no longer relevant.
Some important points about the Guard Timer are as follows:
•
When the Guard Timer is running, any R-APS messages received are not forwarded.
•
The Guard Timer value must be greater than the maximum expected forwarding delay time for which it
takes one R-APS message to circulate around the ring. This calculated value is required to prevent any
looping scenarios within the ring.
•
Refer to the
"ERP Specifications" on page 9-2
How Does ERP Work?
ERP operates over standard Ethernet interfaces that are physically connected in a ring topology. It uses an
Automatic Protection Switching (APS) protocol to coordinate protection and recovery switching mecha-
nisms over the Ethernet ring.
In an Ethernet ring, each node is connected to two adjacent nodes using two independent links called ring
links. A ring link is bound by two adjacent nodes on ports called ring ports. The ring nodes support stan-
dard FDB (Filtering database) MAC learning, forwarding, flush behavior, and port blocking and unblock-
ing mechanisms.
The Ethernet ring has a designated Ring Protection Link (RPL), which is blocked under normal conditions
in order to avoid forming a loop in the ring. When a link or port failure is detected, a Signal Failure (SF)
message is sent on the ring to inform other ring nodes of the failure condition. At this point the ring is
operating in protection mode. When this mode is invoked, the RPL is unblocked forming a new traffic
pattern on the ring, (for example, traffic is accommodated on the RPL but blocked on the failed link). The
node responsible for blocking and unblocking the RPL is called the RPL Owner.
ERP Ring Modes
A ring operates in one of two modes: idle (normal operation; all links up and RPL is blocked) and protec-
tion (protection switching activated; a ring failure has triggered the RPL into a forwarding state).
The following illustration shows an example of an ERP ring operating in the idle mode; all ring nodes are
up and the RPL is blocked:
page 9-4
for timer defaults and valid ranges.
for timer defaults and valid ranges.
OmniSwitch AOS Release 7 Network Configuration Guide
Configuring ERP
March 2011
Advertisement
Table of Contents
