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Packet Detection

For GRE tunnel interfaces, the event that triggers dynamic creation of subscriber interfaces occurs when the router receives a packet with a source IP address that is not in the demultiplexer table. In this case, the primary IP interface must be in autoconfiguration mode.

Packet detection is the only method of dynamically creating subscriber interfaces on GRE tunnel interfaces; you cannot use DHCP local server or DHCP external server.

Issuing the ip auto-configure ip-subscriber command configures the primary IP address to enable dynamic configuration of subscriber interfaces. Unlike DHCP configurations, the router creates the dynamic subscriber interface when it receives the first packet that contains the subscriber’s IP address as the source address.

In addition, a dynamic subscriber interface becomes inactive after a period of time in which the router receives no packets that contain the subscriber’s IP address as the source address. You can configure the period of time by issuing the ip inactivity-timer command.

To configure dynamic creation of subscriber interfaces on GRE tunnel interfaces, see Configuring Dynamic Subscriber Interfaces.

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