Interface takeover function and gratuitous ARP

Answer

TCPIP dynamically learns of redundant interfaces on a LAN, creating a LanGroup for each LAN. TCPIP will manage ARP flow for each LanGroup detected. Each interface will respond to ARP requests for the interface's unique IP address . If VIPA interfaces are configured, one interface will be selected from the LanGroup to respond to ARP requests for each VIPA address defined to the TCPIP stack. When a new VIPA is added to the TCPIP stack, a gratuitous ARP will be sent out each LanGroup, advertising the VIPA address is associated with the interface. If one of the interfaces in the LanGroup becomes inactive for any reason, another interface in the LanGroup will be assigned ARP responsibility for any IP addresses assigned to the inactive interface. Gratuitous ARPs will be sent out for each of the IP addresses being taken over.

For example, suppose a TCPIP stack has 4 OSA interfaces defined, along with 2 VIPA addresses: 10.1.1.1 and 10.100.100.1.

Two LanGroups would be created for this environment:

LanGroup: 001    LnkName   LnkStatus   ArpOwner   VipaOwner    -------   ---------   -------    ---------    OSA1      Active      OSA1       yes    OSA2      Active      OSA2       no  LanGroup: 002    LnkName   LnkStatus   ArpOwner   VipaOwner    -------   ---------   --------   ---------    OSA3      Active      OSA3       no    OSA4      Active      OSA4       yes

OSA1 and OSA4 will send gratuitous ARPs out for both the 10.1.1.1 and 10.100.100.1 VIPA addresses. If OSA1 becomes inactive for any reason, OSA2 will send out a gratuitous ARP for the physical address of OSA1 and for VIPA addresses 10.1.1.1 and 10.100.100.1. The LanGroups will then look like:

LanGroup: 001    LnkName   LnkStatus   ArpOwner   VipaOwner    -------   ---------   -------    ---------    OSA1      Not Active  OSA2       no    OSA2      Active      OSA2       yes  LanGroup: 002    LnkName   LnkStatus   ArpOwner   VipaOwner    -------   ---------   --------   ---------    OSA3      Active      OSA3       no    OSA4      Active      OSA4       yes