Managing Serviceguard 11th Edition, Version A.11.16, Second Printing June 2004

Understanding Serviceguard Software Components
How the Network Manager Works
Chapter 3 99
Local Switching
A local network switch involves the detection of a local network interface
failure and a failover to the local backup LAN card. The backup LAN
card 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,
Token Ring and FDDI use 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 configuration is supported:
• 1000Base-SX and 1000Base-T
• 1000Base-T or 1000BaseSX and 100Base-T
On HP-UX 11i, however, Jumbo Frames must not be used since the
100Base-T cards do not support Jumbo Frames. 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 FDDI interfaces is not supported, but
a local switchover between 10BT Ethernet and 100BT Ethernet is
supported.