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JUNOS 10.1 Network Interfaces Configuration Guide
RAPS Message Blocking and Forwarding
The router treats the ring automatic protection switching (RAPS) message the same
as 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 between the two ring ports,
as shown in Figure 69 on page 854, 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 through the ring ports, as
shown in Figure 70 on page 854. 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 69: Protocol Packets from the Network to the Router
Incoming ring port, R_APS multicast MAC address
(01-19-a7-00-00-01)
Figure 70: Protocol Packets from the Router to the Network
CPU, R_APS multicast MAC address
(01-19-a7-00-00-01)
Juniper Networks routers use an implicit filter to achieve these routes. Each implicit
filter binds to a bridge domain. Therefore, the east ring port control channel and the
west ring port control channel of a particular ring instance must be configured to the
same bridge domain. For each ring port control channel, a filter term is generated
to control RAPS message forwarding. The filter number is the same as the number
of bridge domains that contain the ring control channels. If a bridge domain contains
control channels from multiple rings, the filter related to this bridge domain will have
multiple terms and each term will relate to a control channel. The filter has command
parts and control-channel related parts, as follows:
854
Understanding Ethernet Ring Protection Switching Functionality
Common terms:
term 1: if [Ethernet type is not OAM Ethernet type (0x8902)
]
{ accept packet }
term 2: if [source MAC address belongs to this bridge]
{ drop packet, our packet loop through the ring and come back
to home}
term 3: if [destination is the RAPS PDU multicast address(0x01,0x19,0xa7,
0x00,0x00,0x01] AND[ring port STP status is DISCARDING]
{ send to CPU }
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)
east ring port (STP index state does not apply)
west ring port (STP index state does not apply)
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