The VARP module functionality analysis and design

The main goal the VARP mdule is to maintain coherent VARP tables. It updates the vrouter's VARP table using the informations in the VARP messages received by the interface and answers to VARP requests by sending VARP responses. It also sends VARP requests when VARP entries are expired.

Two processes implement these functionalities. I will call them VARP Primary Daemon and VARP Sheduler. In the following I will give details about these two processes :

• The VARP Primary Daemon : This is an interface dependant process, spawned for every newly added interface, and takes part of the interface-dependent network stack. The main role of this sub-module is to process VARP messages received by the corresponding interface. The VARP message processing follows the standard ARP specifications, so, I will not explain it in this document ( see RFC 826 for more details about the ARP protocol ). the VARP Primary daemon is spawned by calling the function varp_startup function.

• The VARP Scheduler : This process is global and common for all interfaces ( ie. not interface-dependant ). It is spawned when adding the first interface to the router. The role of this process is to expire old VARP entries and send VARP requests to renew them, otherwise flush the VARP table and delete the obsolete entries.

  The VARP module offers function to send VARP packets when adding a new interface to tell the neighbours host about the new interface. These functions are used by the VIF module and are not attached to the VARP Primary Daemon neither to the VARP scheduler.