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Community Member

Redundant TN3270 server

How can redudant TN3270 server be implemented with 2 x 7206 each with CPA as follows?



Can this be implemented using Hot Standby MAC address (HMAC) introduced in 12.(3)?

From the following HMAC configuration,

interface Channel1/0

csna 0190 09

lan TokenRing 20

source-bridge 310 3 100

adapter 9 4043.1313.9009 hsma-partner 4043.3333.001a

lan TokenRing 26

source-bridge 319 9 100

adapter 26 4043.1111.001a

hsma enable

Is adapter for HSMA required to be defined in XCA?

Cisco Employee

Re: Redundant TN3270 server

HSMA designed so that you can have CPA adapters

with duplicate MAC addresses in an ethernet environment. It works by keeping one of the 2 adapters inactive. There is an LLC session between the HSMA control adapters that is used to determine which adapter should be active and to determine whether the other adapter is alive.

There is a tn3270 server design guide at

Community Member

Re: Redundant TN3270 server

Do we have to define the HSMA adapter 26 in XCA?

Cisco Employee

Re: Redundant TN3270 server

No. Adapter 26 is the HSMA control adapter. The MAC address on the control adapter needs to match the MAC coded as the HSMA partner on the other CPA.


Community Member

Re: Redundant TN3270 server

Can the following configuration with 2 or more PU sharing the same IP address?


pu A3270PU 05D0100A token-adapt 3 40

rmac 4000.1111.1111 lu-seed A3270L##

pu BRAHMPU2 05D76543 token-adapter 3 50

rmac 4000.1111.1111 lu-seed PADMA##

I have the following queries also:

1. What is the advantage of having multiple PUs sharing the same IP address?

2. Can this be used for redundancy purpose?

3. How can the client identify the PU it wants to connect with the same IP address?

Community Member

Re: Redundant TN3270 server

Yes you can share the IP address among multiple PUs.

The easy answer to (1.) is that it's the only way to provide more than 255 LU Sessions (the limit for a PU Type 2 device) at a single IP address. For (2.) the answer is that it hints at the more complete answer below. And the answer to (3.) is that you can't, that it shouldn't matter, only what LU it connects to, and again see more below.

In the simplest design, all of the LUs would be dynamically created, so would effectively be one large pool, and you wouldn't care which IP address or token adapter the client attached to. For most people, some or most of their TN3270 works this way. But most also have some applications for which they need to have a deterministic mapping between TN3270 Client and SNA LU. So they will have multiple IP address's, some representing pools of LUs, and some representing specific, or small groups of, LUs.

Within these constraints there are options for how the specific LUs are created. Ranging from static pre definitions, through the lu-seed wildcard naming shown in your sample, to taking the names directly from TN3270E Clients. The last of these allowing the possibility of moving all sessions into the large pool model, but at the cost of implementing and maintaining client configurations. There's more on this, and better addressed, in the design guide.

What I think is important though, is that it is the IP side of the TN3270 Server that can provide the better hot standby - high availability solution. Because it's a TCP connection, any of a variety of load balancing products or features, from NAT, Local Director, Distributed Director,... through CSM and CSS can be used to send connections to the best and/or an available TN3270 Server. As a starting point you may want to consider the advantages of all clients connecting to DNS supplied names, rather than to a coded IP address.

Community Member

Re: Redundant TN3270 server

What is the maximum number of PUs defined with a single "listen-point IP" for TN3270? It seems that it cannot support more than 4 PUs with a single "listen-point IP" as follows:



pu pu1 0012001 token-adapter 2 40

pu pu2 0012002 token-adapter 2 44

pu pu3 0012003 token-adapter 2 48

pu pu4 0012004 token-adapter 2 4c

pu pu5 0012005 token-adapter 2 4f

Community Member

Re: Redundant TN3270 server

You should be able to create a much larger number of PUs. The last parameter in your example is the key. It's the Local SAP (lsap), and has a range of 04 to DE in multiples of 2, which yields 109 possibilities.


You may want to also have a look at the Configuration and Design Guides.




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