Unanswered Question
Sep 11th, 2010
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Hi experts,

Anybody have idea of what is SDR in IOS-XR , i have gone through cisco documents in below link but really

not getting what it is.

Please help me to understand the same.

Thanks & Regards


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Giuseppe Larosa Sat, 09/11/2010 - 04:42
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Hello Mahesh,

these high end carrier class routers can be divided into separate logical systems, and each of these logical routers uses part of hardware and it is like a stand alone router.

So SDR is simply the process of managing logical systems/routers on IOS XR.

This concept is new, as  it is not present in standard IOS.

Actually, there is an admin environment other then enabled and configuration mode.

In this admin mode the logical systems are defined and what linecards are in use by a specific logical system/SDR is defined

Also some maintanance tasks are performed in admin mode

Hope to help


Mahesh Gohil Sat, 09/11/2010 - 18:23
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Hi Giuseppe,

Expecting your reply on this new concept, however i am bit confused here about logical system,

my confusion:

This logical system is per user or what ?

If i am doing changes in any logical system will it affect rest of the main hardware ?

How each logical system corelate to different processes.?

confusion is more but i am sure you will throw it to some corner. You can also refer me to some document which i will read and

try to understand.



Jon Marshall Sun, 09/12/2010 - 05:11
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Think of SDR as the ability to have multiple virtual routers on the same physical hardware. So it's not per user or anything like that, it is simply you can have multiple logical routers and you can use these routers as you would a single physical router. It's like using contexts on the ASA or FWSM firewalls if you are familiar with them.

Each logical router has it's own configuration, it's own routing tables, runs it's own routing protocols and these are totally independant of each other. However the logical routers share the physical switch fabric and hardware of the physical chassis. You basically assign certain parts of the hardware to a logical routers.

So a practical application would be you could be servicing multiple customers and each customer could be allocated a logical router on the same physical chassis. This allows you to route that customers traffic totally independantly of the other logical routers and there is no danger of routes getting mixed up. It also has the advantage that if you make a mistake in one logical routers in terms of configuration it will not have an affect on any of the customers using different logical routers on the same chassis.


Mahesh Gohil Sun, 09/12/2010 - 20:24
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Hi jon,

This seems to be good explanation. but want to know how this is useful to me as I am using GSR as a core router

having only mpls ldp running and there is no vrf or bgp kind of stuff.

Please help to get this understanding .

once again thanks for your explanation.




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