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RAPS Message Blocking and Forwarding

The router treats the RAPS message 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, 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 is physical interfaces STP index state. The RAPS message is always sent by the router through the ring ports. An 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.

Protocol packets from network to the router:

                                 |-- other ring port (STP index state applies
                                 |   on this port and the incoming ring port)
                                 |
    Incoming ring port,          | 
    RAPS multicast MAC address---|
    (01-19-a7-00-00-01)          |-- CPU (Ethernet ring module)
                                     (STP index state does not apply on the 
                                      incoming ring port)

Protocol packets from router to the network:

                                 |---- east ring port 
                                 |     (STP index state does not apply)
                                 |
CPU, RAPS multicast MAC address--|
    (01-19-a7-00-00-01)          |  
                                 |-----west ring port 
                                 |     (STP index state does not apply)

Juniper Networks uses 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:

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 }

Control channel related terms:



      if [destination is the RAPS PDU multicast address(0x01,0x19,0xa7,0x00,0x00,
         0x01] AND[ring port STP status is FORWARDING] AND [Incoming interface
          IFL equal to control channel IFL]
         { send packet to CPU and send to the other ring port }
      default term: accept packet.

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