Novell BUSINESS CONTINUITY CLUSTERING 1.1 SP2 - ADMINISTRATION, Administration Manual, Page: 96 / 142

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Figure 8-2
Multihomed Server Using Virtual IP Addresses
In this configuration, if the 1.1.1.1 interface were to fail, the client would ultimately learn the new
route through Router 2 and would correctly forward packets to Router 2 instead of Router 1. Thus,
despite physical interface failures, a virtual IP address on a multihomed server acts as an always-
reachable IP address for the server.
Generally speaking, if a connection between two machines is established by using a virtual IP
address as the end-point address at either end, the connection is resilient to interface failures at either
end.
There are two important side effects that directly follow from the highly reachable nature of virtual
IP addresses:
Š They completely and uniquely identify a multihomed server
A multihomed server with a virtual IP address no longer needs to carry multiple DNS entries
for its name in the naming system.
Š
They significantly enhance the LAN redundancy inherent in a multihomed server
If one of the subnets that a server interfaces to fails completely or is taken out of service for
maintenance, the routing protocols reroute the packets addressed to the virtual IP address
through one of the other active subnets.
The resilience against interface failures provided by virtual IP addresses depends on the fault
resilience provided by the dynamic routing protocols, as well as on fault recovery features such as
retransmissions built into the application logic.
3.3.3.3
Client
3.3.3.2
Router 2 Router 1
2.2.2.2
Server
2.2.2.1 1.1.1.1 X
1.1.1.2
3.3.3.1
4.4.4.1 (Virtual IP)