Managing Serviceguard A.11.20, March 2013

◦ The primary switch should be directly connected to its standby.
◦ There should be no single point of failure anywhere on all bridged nets.
NOTE: You can change the value of the NETWORK_FAILURE_DETECTION parameter while the
cluster is up and running.
Local Switching
A local network switch involves the detection of a local network interface failure and a failover to
the local backup NIC (also known as the standby NIC). The backup NIC must not have any IP
addresses configured.
In the case of local network switch, TCP/IP connections are not lost for Ethernet, but IEEE 802.3
connections will be lost. For IPv4, Ethernet uses the ARP protocol, and HP-UX sends out an unsolicited
ARP to notify remote systems of address mapping between MAC (link level) addresses and IP level
addresses. IEEE 802.3 does not have the rearp function.
IPv6 uses the Neighbor Discovery Protocol (NDP) instead of ARP. The NDP protocol is used by
hosts and routers to do the following:
• determine the link-layer addresses of neighbors on the same link, and quickly purge cached
values that become invalid.
• find neighboring routers willing to forward packets on their behalf.
• actively keep track of which neighbors are reachable, and which are not, and detect changed
link-layer addresses.
• search for alternate functioning routers when the path to a router fails.
Within the Ethernet family, local switching is supported in the following configurations:
• 1000Base-SX and 1000Base-T
• 1000Base-T or 1000BaseSX and 100Base-T
On HP-UX 11i, however, Jumbo Frames can only be used when the 1000Base-T or 1000Base-SX
cards are configured. The 100Base-T and 10Base-T cards do not support Jumbo Frames.
Additionally, network interface cards running 1000Base-T or 1000Base-SX cannot do local failover
to 10BaseT.
During the transfer, IP packets will be lost, but TCP (Transmission Control Protocol) will retransmit
the packets. In the case of UDP (User Datagram Protocol), the packets will not be retransmitted
automatically by the protocol. However, since UDP is an unreliable service, UDP applications
should be prepared to handle the case of lost network packets and recover appropriately. Note
that a local switchover is supported only between two LANs of the same type. For example, a local
switchover between Ethernet and IPoIB interfaces is not supported, but a local switchover between
10BT Ethernet and 100BT Ethernet is supported.
Figure 25 shows two nodes connected in one bridged net. LAN segments 1 and 2 are connected
by a hub.
How the Network Manager Works 71