The operator can enable the following CE address discovery processes by configuring the ce-address-discovery in the config>service>ipipe context.
The service is brought up without the CE address parameter configured at either the SAP or the spoke-SDP.
The operator cannot configure the ce-address parameter under the config>service>ipipe>sap or config>service>ipipe>spoke-sdp context when the ce-address-discovery in the config>service>ipipe context is enabled. Conversely, the operator is not allowed to enable the ce-address-discovery option under the Ipipe service if it has a SAP and, or spoke-SDP with a user-entered ce-address parameter.
While an ARP cache is empty, the PE does not forward unicast IP packets over the Ethernet SAP but forwards multicast/broadcast packets. target IP address being resolved.
The PE waits for an ARP request from the CE to learn both IP and MAC addresses of the CE. Both entries are added into the ARP cache. The PE accepts any ARP request message received over Ethernet SAP and updates the ARP cache IP and MAC entries with no further check of the source IP address of the ARP request message or of the target IP address being resolved.
The 7450 ESS, 7750 SR, and 7950 XRS routers always reply to a received ARP request message from the Ethernet SAP with the SAP MAC address and a source IP address of the target IP address being resolved without any further check of the latter.
If the router received an address list TLV from the remote PE node with a valid IP address of the CE attached to the remote PE, the router does not check the CE IP address against the target IP address being resolved when replying to an ARP request over the Ethernet SAP.
The ARP cache is flushed when the SAP bounces or when the operator manually clears the ARP cache. This results in the clearing of the CE address discovered on this SAP. However, when the SAP comes up initially or comes back up from a failure, an unsolicited ARP request is not sent over the Ethernet SAP.
If the Ipipe service uses a spoke-SDP, the router includes the address list TLV in the interface parameters field of the pseudowire Forwarding Equivalent Class (FEC) TLV in the label mapping message. The address list TLV contains the current value of the CE address in the ARP cache. If no address was learned, an address value of 0.0.0.0 must be used.
If the remote PE included the address list TLV in the received label mapping message, the local router updates the remote PE node with the most current IP address of the Ethernet CE using a T-LDP notification message with the TLV status code set to 0x0000002C and containing an LDP address list. The notification message is sent each time an IP address different from the current value in the ARP cache is learned. This includes when the ARP is flushed and the CE address is reset to the value of 0.0.0.0.
If the remote PE did not include the address list TLV in the received label mapping message, the local router does not send any notification messages containing the address list TLV during the lifetime of the IP pseudowire.
If the operator disables the ce-address-discovery option under the VLL service, service manager instructs LDP to withdraw the service label and the service is shutdown. The pseudowire labels are only signaled and the service comes up if the operator re-enters the option again or manually enters the ce-address parameter under SAP and spoke-SDP.