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    Managing Address Changes Received from Remote Endpoints

    A remote endpoint can use the Start-Control-Connection-Reply (SCCRP) packets that it sends to the E Series LAC to change the address that the LAC uses to communicate with the endpoint. By default, the LAC accepts the change and uses the new address to communicate with the endpoint. However, you can configure the LAC to ignore or reject the requested change. Setting up the LAC to ignore address changes in SCCRP packets enables the router to construct tunnels with separate receive and transmit addresses and to avoid problems due to a misconfiguration. Three possible configurations are available:

    • Default configuration—The E Series LAC accepts the change from the endpoint. The LAC then sends all subsequent packets to, and accepts packets from, the new address.
    • Ignore configuration (specified by the l2tp ignore-transmit-address-change command)—The LAC continues to send packets to the original address but accepts packets from the new address.
      host1(config)#l2tp ignore-transmit-address-change Use the ip-address or udp-port keyword to ignore the specific address component. Omit the keywords to ignore the entire address change in the SCCRP packet.
    • Reject configuration (specified by the l2tp reject-transmit-address-change command)—The LAC sends a Stop-Control-Connection-Notification (StopCCN) to the original address, then terminates the connection to the endpoint.
      host1(config)#l2tp reject-transmit-address-change ip-address

      Use the ip-address or udp-port keyword to reject the specific address component. Omit the keywords to reject the entire address change in the SCCRP packet.

      Note: When an L2TP hello message contains a non-zero value in the Reserved Bits field of the L2TP message header, and the LAC rejects the change in the endpoint address by sending a StopCCN to the original address, the Result Code field contains the value of 2 and the Error Code field contains the value of 3. The Result code value denotes a generic error, while the Error code value denotes that one of the field values was out of range or the Reserved Bits field was non-zero in the StopCCN message sent from the LAC to the endpoint.

    The reject specification takes precedence over the ignore specification.

    The router accepts a change in receive address only once, during the tunnel establishment phase, and only on an SCCRP packet. Subsequent changes result in the router dropping packets. Any changes do not affect established tunnels.

    Use the show l2tp command to display the SCCRP address change configuration.

    Published: 2014-08-20