TCP/IP (Parallel Library) Configuration and Management Manual

Introduction
HP NonStop TCP/IP (Parallel Library) Configuration and Management Manual—522271-006
2-8
Ethernet Failover
A shared IP failover pair also requires that a second IP address, referred to as the
reserved IP address, be configured on each SUBNET in the pair. This address must be
unique in the network and must reside on the same network subnet as the shared IP
address. Parallel Library TCP/IP uses the reserved IP address when issuing Address
Resolution Protocol (ARP) requests to resolve the media access control (MAC)
address to an IP address. By using this reserved IP address, the ARP request does
not affect ARP table entries in other network devices that may currently have sessions
to the failover pair's shared IP address.
When an adapter failure or cabling problem is detected on one of the LIFs of a failover
pair, a gratuitous ARP packet containing the IP address of the failed LIF is sent using
the operational LIF. This causes all devices on the network segment that had ARP
table entries for this address to update their entries with the new MAC address of the
operational LIF. Traffic for all the sessions on the failed LIF migrates to the operational
LIF. When the failure is resolved and the failover pair is configured for non-shared IP,
Parallel Library TCP/IP issues another gratuitous ARP packet on this LIF using its IP
address. This causes all the devices that have sessions to this IP address to change
their ARP table entries again and move the traffic to the new operational LIF. In the
case of shared IP, the gratuitous ARP is not sent but new sessions are distributed over
both LIFs of the failover pair.
If configured for failover, during an adapter upgrade or removal, Parallel Library TCP/IP
detects the LIF unavailability and automatically moves traffic over to the associate LIF.
This feature eliminates the need for manual intervention for migrating traffic.
Reinsertion of a replacement adapter (of the same type and in the same slot)
automatically is detected and the replacement is initialized in the desired failover
configuration. Similarly, if a LIF fails, Parallel Library TCP/IP detects it and moves traffic
to the associate LIF.
Configuration Guidelines
The following are guidelines to use when configuring Parallel Library TCP/IP with
Ethernet failover:
•
When selecting the LIF pair for the failover SUBNET pair, you should select LIFs
on different adapters.
•
When using Fast Ethernet adapters and Gigabit Ethernet adapters connected
directly to Ethernet switches, failover recovery time may be impacted by the
spanning tree feature used in a switch.
•
When using multiple failover pairs on the same network subnet and adding static
routes, it is best to add a copy of each route to one SUBNET in each failover pair.
This increases the availability of the routes should both SUBNETs comprising a
failover pair become unavailable. It also allows Parallel Library TCP/IP to distribute
outbound connections over the failover pairs when the source IP address is not
Note. If you have configured Ethernet failover as non-shared IP, you cannot have a failover
pair consisting of addresses on different subnets.