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layer2-liveness-detection (Receive)


Hierarchy Level


Enable a DHCP client host to determine the state of the DHCPv4 or DHCPv6 client session from the perspective of a router acting as a broadband network gateway (BNG). This statement causes the BNG to conduct a host connectivity check on its directly connected DHCPv4 and DHCPv6 clients when it receives ARP or Neighbor Discovery (ND) packets.

When the BNG receives either of these packets, it does the following:

  1. Checks whether Layer 2 liveness detection for subscriber management is enabled globally for the relevant address family, inet or inet6.

  2. If liveness detection is not enabled, then the BNG responds as usual to the received packets without checking the state of the client session.

    If liveness detection is enabled for the family, then the BNG checks whether the client session is still in the bound state.

  3. If the client session is bound, the BNG responds to the client with the appropriate ARP or ND packet.

    If the session is not bound, the BNG drops the received packet. It does not send an ARP or ND response packet to the host, enabling the host to determine that the BNG considers the session to be down.

This behavior can be referred to as the receive functionality for BNG Layer 2 liveness detection, as opposed to the send functionality configured with the layer2-liveness-detection (Send) statement for DHCP relay or DHCP local server.

The usefulness of the receive functionality depends on the ability of the DHCP client host to reclaim resources from the stale client based on the absence of a response packet from the BNG for an unbound client session. If this capability requires a change in the client implementation, you may want to use the send functionality.

Required Privilege Level

system—To view this statement in the configuration.

system-control—To add this statement to the configuration.

Release Information

Statement introduced in Junos OS Release 17.4R1.