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58 Chapter 2: EIU messaging protocols
297-8991-910 Standard 03.01 August 1999
• Upon failure of any one EIU IP router, the traffic is switched over to
another available (in service) EIU IP router on the same LAN.
• IP routing handles a mix of EIU IP routers and EIU hosts on the same
LAN.
• A simple load balancing scheme between multiple EIU IP routers is
provided. The load balancing scheme sets specific EIUs as primary routers
for the outgoing data. Incoming data is load balanced by specific EIUs that
proxy for host nodes within the SuperNode subnet. As host nodes are
provisioned in table IPHOST, the load balancing scheme is updated. Load
balancing is also updated when nodes go in and out of service.
• The EIU does not route messages between nodes on the same or distinct
LANs. The purpose of an EIU is to provide SuperNode connectivity to the
LAN. It is not intended to act as a router between two Ethernet LANs. The
EIU, however, routes messages to another EIU SuperNode host address if
the other EIU is configured as a host and is connected to a different
Ethernet LAN subnet.
• The IP routing software is identical on all SuperNode nodes, including an
EIU.
• The optional RIP (version 1) is implemented on the EIU to participate in
dynamic routing information exchange. RIP allows the SuperNode switch
to route messages to hosts on distant LANs (nodes not directly connected
on the LAN where EIUs are connected).
• EIUs use proxy ARP for other SuperNode IP hosts and for host EIUs on
other Ethernet LANs.
• When an EIU is ISTb (NA), it is still connected to the Ethernet LAN and
responds to packets received over the LAN. The EIU is aware that the
connection to the SuperNode switch is not available. Awareness is
achieved through the EIU by issuing a reverse RIP to neighboring routers
to indicate that the EIU can no longer route to the SuperNode subnet.
A typical SuperNode network topology that is currently supported is shown in
figure 14 in this chapter.