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Whats so difficult about ISSU



http://www.juniper.net/techpubs/en_US/junos/topics/concept/issu-oveview.html

The Juniper ISSU guide.

You need two things:

1. Separation of the control plane and  forwarding plane
2. 2 routing engines in the same chassis -- the non active RE upgrades 
first, then when its up and running the active one goes into upgrade 
mode and control fails over to the secondary RE which is running the 
upgraded version of the software.

I assume it works on any vendor that has 2 REs in the same chassis and 
the fwd and control planes are separated, and there is a redundancy 
protocol running between the two REs(like Graceful Switchover on Juniper 
gear).

On 11/09/2012 01:42 AM, Kenneth McRae wrote:
> Juniper also offers it on the EX virtual switching platform.  Works if you
> have the correct version of JunOS.
>
> On Thu, Nov 8, 2012 at 3:38 PM, Zaid Ali <zaid at zaidali.com> wrote:
>
>> Cisco Nexus platform does it pretty well so they have achieved it.
>>
>> Zaid
>>
>> On Nov 8, 2012, at 3:22 PM, Kasper Adel wrote:
>>
>>> Hello,
>>>
>>> We've been hearing about ISSU for so many years and i didnt hear that any
>>> vendor was able to achieve it yet.
>>>
>>> What is the technical reason behind that?
>>>
>>> If i understand correctly, the way it will be done would be simply to
>> have
>>> extra ASICs/HW to be able to build dual circuits accessing the same
>> memory,
>>> and gracefully switch from one to another. Is that right?
>>>
>>> Thanks,
>>> Kim
>>
>>