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# Configuring the Length of Time MAC Addresses Remain in SAE Cache

When a DHCP subscriber transitions from an authenticated IP address to an unauthenticated IP address or vice-versa, the SAE:

1. Logs out the subscriber associated with the original IP address.
2. Caches the subscriber profile in the in-memory cache, indexed by the DHCP subscriber’s MAC address.
3. Waits until the DHCP subscriber with the cached MAC address obtains its new IP address, and then logs in the subscriber and associates it with the new IP address.

The period during which the subscriber profile remains in the in-memory cache can last until the DHCP lease time for the original address. If something happens during this period—for example, the subscriber turns off the client computer—the subscriber profile remains in the SAE’s in-memory cache forever. When a new IP address is assigned to the same DHCP client, problems can occur. To avoid such problems, entries in the in-memory cache are removed after a configurable amount of time.

Configure the amount of time that entries remain in cache to be greater than the time required for a DHCP subscriber to transition from an unauthenticated IP address to an authenticated IP address or vice versa. The time required for a DHCP subscriber to transition from one IP address to another depends on the lease times configured on the JUNOSe router and the instructions given to the subscriber on the Web portal, such as reboot your PC now.

Use the following configuration statement to configure the length of time that a subscriber profile remains in the SAE’s in-memory cache:

`

shared sae configuration driver {
  mac-cache-expiration mac-cache-expiration;
}

`

To configure the amount of time that subscriber profiles remain in the SAE’s in-memory cache:

1. From configuration mode, access the SAE driver configuration statement.
   `
   user@host# edit shared sae configuration driver
   `
2. Specify the amount of time that subscriber profiles remain in the SAE’s cache.
   `
   [edit shared sae configuration driver]
   user@host# set mac-cache-expiration mac-cache-expiration
   `
3. (Optional) Verify your configuration.

       [edit shared sae configuration driver]
       user@host# show mac-cache-expiration
       mac-cache-expiration 1800;

#### Related Topics

- Configuring the Length of Time That MAC Addresses Remain in SAE Cache (C-Web Interface)
- DHCP Subscriber Login and Service Activation

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