> > We have here a mainframe that speaks SNA and TCP/IP. We are migrating
> > some applications to SUN machines that do not speak SNA. We'd like to
> > migrated the existing SNA links to routers. Is it possible to translate
> > SNA to TCP/IP and vice versa using a router as a gateway? Has anyone
> > ever seem this?
> Correct me if I'm wrong. I'm not CCIE certified yet. But yes, Its
> being used all over the world. Mainframes was save from being
> extinct because cisco came up a way to network sna traffic with ethernet
> traffic. Source route translational bridge (SRTB) has to be configure on
> the router. SRTB is a combination of transparant bridging and source
> routing bridging. Ethernet uses transparant bridging because the
> network is transparant to the end users. Mainframes run only on
> token-ring networks so it only uses source-route bridging. So therefore,
> SRTB needs to be in effect.
Firstly, it is possible to migrate networks such that IP clients are able to
talk to a mainframe talking SNA. The ONLY method of doing this is to use
TN3270 server, which, in the Cisco world, runs either on the Channel Port
Adapter (CPA) or the Channel Interface Processor (CIP). There are many other
benefits to using a CPA or CIP in the 7000 series routers, although nowadays
both IBM and Cisco are recommending the approach of using OSA Express
adapters in the S/390 and running TCP/IP directly on the S/390.
Source-Route Translational Bridging (SR/TLB) is at best a horror show and at
worst a network administrator's worst nightmare. It is categorically *NOT* a
solution for enabling IP clients running TN3270 to talk to an SNA host.
Bridging, whatever flavour it may be, will only convert the Data Link
Layer/Media Access Control information, i.e. Layer 2 framing. There is no
knowledge of, nor any need to manipulate, Layer 3 information at this layer.
SR/TLB is only recommended if there are Ethernet- and Token Ring-attached
PUs in the network, which are talking SNA and must talk to a S/390.
Typically, this environment involves the S/390 being Token Ring connected
and the clients are on Ethernet. SR/TLB is a kludge to get working and is
not advisable if you are at all able to avoid it. It is far better to use a
router and have the clients use TCP/IP and TN3270 to talk to the S/390. The
S/390 may be assisted by the presence of a Cisco 7000 series router, on
which you could run TN3270 server, but this is also no longer necessary. It
depends on your network.
Cisco's original strategy was to convince IBM customers that there were good
reasons to ditch the Front End Processors (FEPs, typically 3745s or 3746s),
namely the costs of maintaining these devices and especially the NCP
licences, which are very expensive. Placing a Cisco 7000 series router with
an ESCON interface (licensed to Cisco by IBM) in front of the S/390 meant
that the FEP would be redundant and could be easily replaced by the router,
which was able to handle all these functions.
The recommended method of providing S/390 connectivity today is to use the
OSA Express adapters, as they are able to bypass the mainframe bus
architecture and make use of a type of Direct Memory Access method, which is
not limited by bus speed, which is the case with the ESCON interface. Most
enterprises will continue to run SNA at the S/390 level for some years to
come, but IBM and Cisco are proposing alternatives to this, which involves a
gradual transition from Token Ring to Ethernet and from SNA to IP, right up
to S/390 level. It really is only the older S/390 that you have to be
concerned about, as the OSA Express adapter is not compatible with the older
systems. Then you could continue to use the 7000 series router as a
front-end.
--
Edward Solomon
CCNA, CCSI
Senior I/T Specialist
Networking Solutions
IBM Canada Ltd. - Learning Services
Tel.: (905) 316-3241 Fax: (905) 316-3101
E-mail: [EMAIL PROTECTED]
Internet: http://www.can.ibm.com/services/learning/net_internet.html
___________________________________
UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html
FAQ, list archives, and subscription info: http://www.groupstudy.com
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
