IBM Mainframe Forum

Dear Group,

Is it possible to assign two subnet IP address to one Physical OSA device ?

Any Pointers or suggestions are highly appreciated.

Jaggz

Hi.

As far as I know it is not directly possible to define multiple IP addresses to one OSA. The definition should be rejected by the stack.

But what you can do is to define VLANs for your OSA Express. It is possible to define up to 32 VLANs (since V1R12, on older releases 8 VLANs) per physical OSA.
What you should consider: When you define VLANs for the OSA you need one datapath in the TRL definition for each VLAN. Also consider to use VMAC support.
The Router/Switches connected to the OSA should use trunc mode instead of access mode if you define VLANs.

There are very good examples and hints in the Communications Server Implementation Redbook (Volume 1) for VLAN definitions.
Perhaps you'll get there more detailed information.

Regards

Hello Shady,

Thanks for your reply. Yes we do not have the additional hardware to connect to the new subnet. The existing primary Subnet is exhausted with all the available IP address but i am just curious to know if we can use the secondary subnet IP address available by defining VLANS to the OSA express.

Jaggz

Hello jaggz,

what I understood is that you need an additional IP range because you run out of the old.

Now you've to consider what would you want to reach with the new subnet:
* Should all applications be autarkic from all others
* Should both subtnets be able to communicate with each other
* Are you considering in setting up a new LPAR or something (If your approach is to create a new LPAR or something, than you won't need all that. The OSA can be shared between them. So I suppose you don't want to create a new LPAR, right?)
...

Just after thinking one minute I see two alternatives (for sure there are more):
1. You just need to propagate a new range and the outside world must also propagate
2. You configure VLAN support with trunking on the switch ports

In both cases you'll need the support of the network stuff on your side.

To 1:
This is something we also do.
Just as example: You've the range 172.16.0.0/16 for your z/OS. Now you need to expand that because you running out of IPs.
You also have a range of 192.168.0.0/24. You know this range is absolutly unused in the network. Than your network stuff can define routes in the routers where to reach that range (on the mainframe). The only thing you have to do is that you also have to propagate that range. This is the part of OMPROUTE (I consider you use OMPROUTE?).
With that solution you won't need a OSA port within the 192.168.0.0/24 subnet.

To 2:
The other way, VLANs:
Example: You've actually the following interface definition (DEV/LINK/HOME, whatever):
INTERFACE OSA01IF
IPAQENET
PORTNAME OSA01
IPADDRESS 172.16.0.1/16
SOURCEVIPAINT VLINK1
MTU 1500

Also in that case you need the other range, 192.168.0.0/24
When you define it as VLANs you have to delete the old interface definition and to redefine it with VLAN.
Please note: Your network support must offer you the VLAN IDs, they must match. They also must define the switch ports as trunc ports.
The new definition can look like that:

INTERFACE OSA01IF
IPAQENET
PORTNAME OSA01
IPADDRESS 172.16.0.1/16
MTU 1500
SOURCEVIPAINT VLINK1
VLAN 10

INTERFACE OSA01IF
IPAQENET
PORTNAME OSA01
IPADDRESS 192.168.0.1/24
MTU 1500
SOURCEVIPAINT VLINK2
VLAN 20

In that way you can define up to 32 VLANs, 32 different networks on the same OSA. Please note: For each VLAN you need a seperate DATAPATH in your TRL definition. The best way in the TRL would be to define one dev for read, one dev for write and the other devs for the CHPID as range for datapaths. VTAM will then allocate the devices. One per VLAN, one per IP Stack (if you have multiple stacks). All others are unused but can used dynamically without updating the TRL (by the way, that is possible on the fly).
At the end of that solution you need to add the new definitions to your OMPROUTE.

BTW: If you consider to cut the new IP range from the old (no access between them) you can also use VLANs. You can set up a firewall by using IP filtering. That wouldn't be practicable because when you logged on from one net or from the other one: The data is the same. I just want to say it is possible.

OK...
Hope that helped you?

Best regards
Shady

Dear Shady,

Thanks a bunch again. My objective was to create a new Z/OS mini on VM. So i just ended up with selecting new Subnet.


I would definetly check on the notes provided by you.

Jaggz