[j-nsp] How to upgrade M20 RE's with least downtime

[Richard A Steenbergen]

On Fri, Nov 12, 2004 at 05:34:00PM -0700, Bill Petrisko wrote:
> On Fri, Nov 12, 2004 at 03:27:33PM -0800, Harry Reynolds wrote:
> > *If* this is within a major version, I have heard that you can get great
> > results by:
> > 
> > 1. Enable Graceful restart to minimize/eliminate forwarding plane
> > disruption
> > 2. Upgrade backup RE
> > 3. Manually switch (here is where graceful restart comes in)
> > 4. Upgrade primary RE
> > 5. If step 3 worked well, switch back
> > 
> > HTHs. Please note Juniper does not claim support for hitless upgrades,
> > but this procedure has been known to result in pretty much that. All
> > bets are off if you are crossing major JUNOS software revisions. You
> > also need to enable graceful restart on peer nodes for it to buy you
> > anything.
> 
> Ok, this is going from 5.6 (no graceful anything) to 6.3.

Having recently done some of of these exact version upgrades myself... 
You're toast on 5.6, but you'll be able to use some graceful functionality 
after you upgrade. Upgrade the 2nd RE, configure graceful restart and 
switchover on it, switch to the backup (and suffer full PFE reboot plus 
full protocol hits), upgrade the primary RE, and optionally switch back 
w/graceful switchover.

> What is the hit time?  (Not including the time for BGP/ISIS/etc
> to reconverge.)

When you do the switch-over, forwarding continues using old state info 
while the sessions are re-established. However, if you're still running 
RE-333's you probably want to increase the default max time for graceful 
restart while the upgraded RE is still in backup mode. If this is a 
peering router with a lot of sessions and/or carries any decent amount of 
protocols (v6, multicast, a few routing instances which require a lot of 
policy processing), you should expect about 15 minutes of churn for full 
convergence. I believe the default time max is only 5 minutes, which you 
may find to be unpleasant about 4 minutes after your switchover. :)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
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