In a purely switch based networking configuration, mutliple subnets may
be defined on a single broadcast domain even if it is accessed by a
single access port (non-VLAN). The default gateway would need to be
configured with addresses for both subnets and for devices on the same
broadcast domain with different subnet addresses to communicate they
would need to go through the default gateway. Admittedly, this violates
the rule of thumb of one subnet per broadcast domain but is supported by
the technology.

What is the source of this restriction?

Harold Grovesteen

Alan Altmark wrote:

On Monday, 04/04/2005 at 11:50 EST, James Melin
<[EMAIL PROTECTED]> wrote:


My TCP/IP situation is such that I had to request a new subnet for my


Linux


environment if we ever want to get to and 'on demand' or any additional
increase in the # of guests. The # of IP addressses left in the current
subnet are few, but I have an entire class C to myself, waiting to be


used.


The problem is:

I have 2 VM systems and 8 linuxes in the old subnet (They have new IP's
waiting)

We are out of open OSA ports - So I cant simply change the VM config to
point to a new set of devices and have the old IP addresses on one VLAN


and


the new ones on another. I am going to have to use the exising port.

Is there a way to mix two subnets on one OSA port so you can have a sane
re-addressing plan?

to rephrase, I would start out with VM and the guests on say
123.231.132.xxx and take a guest, change the configuration so it is


using


123.132.231.xxx but still have everything else still working on the old
subnet but both subnets going out to the switch on the same wire.  Is it
possible or am I going to have to change everything wholesale (VM and


linux


to new subnet) all at once and IPL the universe?



As long as the OSA port is plugged into an access port (non-VLAN) on the switch, no. You're going to have to change all the addresses and reIPL everybody.

Alan Altmark
z/VM Development
IBM Endicott

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