IMS Connectivity in an On Demand Environment: A Practical Guide to IMS Connectivity

Chapter 6. Accessing IMS Connect 81

6.4 Static VIPA

Static VIPA is the term used to refer to the first and simplest implementation of VIPA. It

supports failover from one network interface to another on a single stack, as shown in the

Figure 6-3.

Figure 6-3 Static VIPA

Note that the client application references the target server using the VIPA or a host name

that resolves to the VIPA. In this example, it is 10.0.3.5. The real network interfaces 10.0.1.1

and 10.0.1.2 appear to be intermediate hops. When the connection request is made, one of

the network interfaces, such as 10.0.1.1, is chosen for the connection and all subsequent

data transfer. Only in the event of a physical interface failure associated with 10.0.1.1 will the

traffic be routed to 10.0.1.2. This rerouting will be done non-disruptively without the client

application receiving any notification of a connection failure.

The definition and activation of VIPA is done through configuration statements in the

hlq.profile.tcpip file. IMS Connect is unaware of VIPA. It simply connects to a TCP/IP stack

and relies on the stack to perform the appropriate network function.

Static VIPA only addresses nondisruptive fault tolerance in the case of a specific network

interface failure on a stack. If the stack itself fails, VIPA fails. To move the VIPA to a different

stack a manual, issue the vary obey command.

6.5 Dynamic VIPA takeover

To support recovery of a failed TCP/IP stack and to automate the movement of the VIPA to a

surviving backup stack, the VIPA support was enhanced to include a function called dynamic

VIPA takeover. The use of this capability presumes that server application instances and IMS

Connect instances exist on the backup stack and can serve the clients formerly connected to

the failed stack.

In the example shown in Figure 6-4 on page 82, the dynamic VIPA IP address 10.0.3.5 is

defined as having a

home stack on TCPIPA and a backup on TCPIPB.

TCP/IP

IMS

Connect

Port 5000

10.0.1.1

10.0.1.2

10.0.3.5

OS/390

routers with

dynamic route

updating

remote host

Connect to

port 5000

at 10.0.3.5