Router upgrade....

[Brian Candler]

On Wed, Apr 26, 2006 at 05:48:03AM -0500, Matthew D. Fuller wrote:
> On Wed, Apr 26, 2006 at 10:02:29AM +0200 I heard the voice of
> Tyrone.VanDerHaar at TelecityRedbus.com, and lo! it spake thus:
> > 
> > I would like to upgrade the OS to 6.1RC1 to get the better support
> > for CARP on VLAN interfaces.What would the best way be to upgrade
> > with minimum downtime?
> 
> If it were me, I'd just upgrade the box as-is by buildworld; 5 and 6
> are close enough that major problems aren't too likely (of course,
> this is 'in general'; a single occurance of a major problem isn't much
> globally, but it sure does hurt when it happens to you ;).  Unless
> something goes wrong, your downtime is two reboots.

I think you're forgetting the time sat in single-user mode while doing
installworld and manually mergemaster'ing the rc scripts. For an experienced
admin who has done this many times, it might just be a couple of minutes.
For someone who hasn't done it before, it could be a long outage.

Personally I prefer the other option suggested by the OP:
- build a brand new router using whatever O/S and software revisions you
  choose to be on
- test it to death standalone
- configure it as a replacement and swap it in

If you want it to come up on the same IP address then you may have to clear
ARP caches on some other devices on the same LAN segment(s), but that's
about it. Most importantly, you have a very clear rollback available to you.
I challenge anyone to rollback a "make installworld" :-)

If you are being really clever, you bring it up on different IP address,
then let it take over the traffic (e.g. by participating in OSPF or
whatever, and then the other machine drops out). If there are machines
pointing defaultroute at the old box, then you swap IP addresses between the
boxes. Anyone who has not picked up the new MAC address will still send
traffic via the old box until its ARP cache expires, at which point it will
start using the new. If you are using CARP/VRRP or whatever, it's just a
question of changing the preferences and preemption.

This "smooth" approach may not be practical in your network though (e.g. if
you have a zillion VLANs hardwared into one router or the other)

Regards,

Brian.