[j-nsp] Question about Routing Engine Redundancy on MX

[Doug Hanks]

Harry wrote a great chapter on RE redundancy in the new MX book.

http://tinyurl.com/junipermx


On 1/9/13 11:39 AM, "Harry Reynolds" <harry at juniper.net> wrote:

>My .02.
>
>I too cannot find documentation that mandates the same RE hardware or
>Junos SW for all HA features. The 12.2 HA guide does mandate the same
>version for NSR, and my extension ISSU. (page 80):
>
>http://www.juniper.net/techpubs/en_US/junos12.2/information-products/topic
>-collections/config-guide-high-availability/config-guide-high-availability
>.pdf
>
>IMO, GRES/NSR/ISSU is complex enough. Generally speaking you are only
>adding potential for "less than desirable" outcomes if you attempt to
>deploy such features with mismatched RE hardware or Junos versions. It
>would be safe to say that testing HA features with all possible
>mismatches of RE HW and SW is not done routinely; it may work, or may
>not, and you may well be the first to know, being the first to ever try
>some specific test with some specific set of mismatched HW or SW.
>
>As with all things in life, to some degree success or failure is a matter
>of how significant the mismatch is. Junos 7.0 on master and 12.2 on BU as
>opposed to 12.1R1 vs. 12.1R2; here the later will likely do OK... Same
>with RE hardware. If the master RE is significantly faster or has
>significantly more memory than the BU, you may hit timing issues with
>kernel or NSR synchronization, or, may find that post NSR things go
>poorly as the new master RE struggles to keep up now that it has to run
>the show. If you expect the BU RE to take over with no hit, it's quite
>reasonable to mandate that it at least have the same capabilities as the
>master.... 
>
>In the end it's a complex interaction of how significant the mismatch is,
>whether it effects some key feature that is in use, and the degree to
>which the test box is scaled; in the end its intractable to try and
>predict all the possible permutations.
>
>As a final anecdote, I would never open a PR for a HA feature where the
>DUT had any such mismatch (unless it was a specific feature that mandated
>the disparity), as the first thing the engineer will ask is for me to try
>and repro with matched settings....
>
>HTHs
>
>Regards
>
>
>
>
>
>
>
>-----Original Message-----
>From: juniper-nsp-bounces at puck.nether.net
>[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Paul Stewart
>Sent: Wednesday, January 09, 2013 10:52 AM
>To: 'Jose Sanchez'
>Cc: 'juniper-nsp'
>Subject: Re: [j-nsp] Question about Routing Engine Redundancy on MX
>
>Nothing that I have handy - sorry. we asked this question a few times to
>our Juniper SE and were told that (so presumed it to be factual)
>
> 
>
>J
>
> 
>
>From: Jose Sanchez [mailto:jasjuniper at gmail.com]
>Sent: January-09-13 1:49 PM
>To: Paul Stewart
>Cc: juniper-nsp
>Subject: Re: [j-nsp] Question about Routing Engine Redundancy on MX
>
> 
>
>Thank you,
>
> 
>
>Any link to the documentation that require this?
>
> 
>
>Thanks again
>
> 
>
>Jose
>
> 
>
> 
>
>On Wed, Jan 9, 2013 at 12:43 PM, Paul Stewart <paul at paulstewart.org>
>wrote:
>
>Both same hardware....
>
>
>-----Original Message-----
>From: juniper-nsp-bounces at puck.nether.net
>[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Jose Sanchez
>Sent: January-09-13 1:39 PM
>To: juniper-nsp
>Subject: [j-nsp] Question about Routing Engine Redundancy on MX
>
>Hello,
>
>Does anybody know if the RE Redundancy in Juniper MX Routers requires
>that both RE are the same hardware or it is enough that the REs has the
>same JUNOS Version?
>
>Thanks
>
>Jose
>
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