Juniper ACX2000 Configuration Guide

Traffic Blocking and Forwarding
Ethernet ring control uses the same mechanism as the STP to control forwarding or
discarding of user traffic. The Ethernet ring control module sets the ring port physical
interface default STP index state to forwarding or discarding in order to control user
traffic.
RPL Neighbor Node
Starting with Junos OS Release 14.2, ring protection link neighbor nodes are supported.
An RPL neighbor node is adjacent to the RPL and is not the RPL owner. If a node is
configured with one interface as the protection-link-end and no protection-link-owner
is present in its configuration, the node is an RPL neighbor node.
RAPS Message Blocking and Forwarding
The router or switch treats the ring automatic protection switching (RAPS) message the
same as it treats user traffic for forwarding RAPS messages between two ring ports. The
ring port physical interface default STP index state also controls forwarding RAPS
messages between the two ring ports. Other than forwarding RAPS messages between
the two ring ports, as shown in Figure 15 on page 115, the system also needs to forward
the RAPS message between the CPU (Ethernet ring control module) and the ring port.
This type of forwarding does not depend on the ring port physical interfaces’ STP index
state. The RAPS message is always sent by the router or switch through the ring ports,
as shown in Figure 16 on page 115. A RAPS message received from a discarding ring port
is sent to the Ethernet ring control module, but is not sent to the other ring port.
Figure 15: Protocol Packets from the Network to the Router
Incoming ring port, R_APS multicast MAC address
(01-19-a7-00-00-01)
other ring port
(STP index state applies on this port and the incoming ring port)
CPU (Ethernet ring module)
(STP index state does not apply on the incoming ring port)
g017271
Figure 16: Protocol Packets from the Router or Switch to the Network
CPU, R_APS multicast MAC address
(01-19-a7-00-00-01)
east ring port (STP index state does not apply)
west ring port (STP index state does not apply)
g017270
Juniper Networks switches and Juniper Networks routers use different methods to achieve
these routes.
The switches use forwarding database entries to direct the RAPS messages. The
forwarding database entry (keyed by the RAPS multicast address and VLAN) has a
composite next hop associated with it—the composite next hop associates the two ring
interfaces with the forwarding database entry and uses the split horizon feature to prevent
sending the packet out on the interface that it is received on. This is an example of the
forwarding database entry relating to the RAPS multicast MAC (a result of the show
ethernet-switching table detail command):
115Copyright © 2017, Juniper Networks, Inc.
Chapter 4: Configuring Interfaces and Chassis

Juniper ACX2000 Specifications

General

Brand	Juniper
Model	ACX2000
Category	Network Router
Language	English