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Community Member

SNASW and DLSW on the same router


I have recently moved DLSW+ and SANSw configuration from our wan routers to 7206 dlur routers. Before our wan router were doing wan aggregation along with dlsw and snasw .

Now 7206 routers are only doing dlsw/snasw and WAN routers are only doing wan aggregation for our network.

I am pretty new to IBM networking and like to know what is the advantage and disadvantage of running dlsw/snasw on the same router. We are also planning to move to TN3270 so I think it will be good to have wan router also do snasw and 7206 will only do dlsw+.

Also, how sansw is forwarding papcket to upstrream CIP router which is connected to host via escon. Does packet get encapsulated at 7206 or 7513 CIP routers. Basicclay i need to know how dlsw/snasw traffic is getting encapsulated and where it does get deenvcapsulated.

Any help will be appreciated.

If you need more information please feel free to ask.


Community Member

Re: SNASW and DLSW on the same router


Please refer to this excellent white paper about DLSW+/SNASw deploiement:

This is part of a series of documents on SNASw:

In a nutshell, SNASw talks APPN to the host. DLSW+ and SNASw talk one to each other via DLC (if they are on the same router, they interface via VDLC, Virtual DLC).

I hope this helps.


Community Member

Re: SNASW and DLSW on the same router

I forgot to mention that you can also set up Enterprise Extender (HPR-IP) between SNASw and the host. Traffic would then be UDP over IP.


Community Member

Re: SNASW and DLSW on the same router

Hi Tran,

Thanks for your response and the pointer, but i do have still one questions remaining, where the packet gets encap and decap, is it at CIP rouiter or dlur routers. Also, once we move everyhting to inboard Tn3270 our hardware i mean dlur routers will be useless.Correct ?


Community Member

Re: SNASW and DLSW on the same router

There are different levels of encapsulation; I'll respond from the SNASw perspective.

If you are using the DLUR in SNASw and no EE to the host, then SNASw just forwards the (FID2) LU-LU data, and uses Fid2 Encapsulation GDS variable X'1500' for SSCP-PU/LU sessions with the DLUS.

As little as I know about TN3270, I think that you can use TN3270 server on the CIP to talk directly to the SNA host, or interface with SNASw/DLUR to talk to a or several APPN hosts.


Community Member

Re: SNASW and DLSW on the same router

Hi Javed ,

Much of your end design depends on the number of downstream connections.

I have deployed a 1,000 downstream PU configuration over Frame Relay.

We did use DLSW and SNASW Branch Extender. The PU connections home

to (6) 7206 routers at the datacenter. These 7206 routers run DLSW and SNASW. So, the DLSW LLC connection terminates on the 7206's. The next hop of course is the APPN connection between the same 7206 and your DLUS server. The actual physical routing to the mainframe looks something like this:

PU - sdlc/X.25 - Field Router w/DLSW - Frame Relay with DLSW - Datacenter Frame Router - Fast Ethernet - SNASW/DLSW peer router - Token RIng - 7513 CIP router - CSNA over to ESCON Director - Various LPARS .

Bottom Line:

If you have a few downstream connections and don't plan on much growth, then there's not a problem with merging the technologies, but keep in mind your subjecting yourself to a higher MTBF with more processes running on a single router.

If you have a larger number of downstream connections and want to plan for additional growth, then let your WAN routers handle the circuit aggregation and possibly IP route summarization. Let your back-end 7206 routers handle the DLSW LLC termination and SNASW DLUR functionality. I can tell you, I've been doing this for almost 5 years without a problem. Optionally, you can even break it out further by adding another 7206 layer (one layer for DLSW termination and one for SNASW DLUR), but that's probably an overkill.

In the example above, the 7513 appear as XCA Major Nodes (IBM 3172) to VTAM and the protocol used is CSNA.The example shows a Branch Extender configuration.

You can also configure the 7206 SNASW routers to run Enterprise Extender (HPR). If you go that route, then you're running IP all the way into your Mainframe using HPR and TCP/UDP as a transport. You would need to configure your Mainframe IP stack to terminate the IP stream and configure VTAM appropriately to send and receive the data through your IP stack. Your physical options could use a CIP router or an OSA adapter (OSA Express with Gbit attached to Catalyst swithces preferred method).


Don't use the CIP's TN3270 Server. The best worldclass TN3270 server in my opinion is the TN3270 server provided by IBM running on the Mainframe. I'm referring to the OS/390 eNetwork Communications Server V2R7 or higher. I've tried them all, Cisco CIP, TCP Access from C.A. (the old Interlink), Microsoft's SNA Server, IBM's AIX, etc. They can't compare to the inherit features of the IBM server.

Note: I'm currently running z/OS V1 R2. I am using the TN3270 server in production and I'm getting ready to use the SSL features.

Hope this helps!

Brian M. Kelley

Community Member

Re: SNASW and DLSW on the same router

Thanks Brian,

Very useful information , i really appreciate your help my friend. it looks like you have good experience in IBM networking which I dont ;)

take care

Community Member

Re: SNASW and DLSW on the same router

No problem! Good Luck!


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