Re: [PATCH RFC 00/24] IPVS: Add first IPv6 support to IPVS

To: Julius Volz <juliusv@xxxxxxxxxx>
Subject: Re: [PATCH RFC 00/24] IPVS: Add first IPv6 support to IPVS
Cc: Sven Wegener <sven.wegener@xxxxxxxxxxx>, Graeme Fowler <graeme@xxxxxxxxxxx>, netdev@xxxxxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, kaber@xxxxxxxxx, vbusam@xxxxxxxxxx
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Thu, 28 Aug 2008 09:49:16 +1000
On Wed, Aug 27, 2008 at 05:24:53PM +0200, Julius Volz wrote:
> On Wed, Aug 27, 2008 at 8:09 AM, Simon Horman <horms@xxxxxxxxxxxx> wrote:
> > On Fri, Aug 22, 2008 at 02:14:11PM +0200, Julius Volz wrote:
> >> On Fri, Aug 22, 2008 at 1:23 PM, Sven Wegener <sven.wegener@xxxxxxxxxxx> 
> >> wrote:
> >> >> He :) Imagine an old kernel on the backup receiving new messages and
> >> >> not understanding them. How could we at least handle that situation
> >> >> gracefully (without totally confusing the older kernel)? We'd need to
> >> >> do it in a way that old features are still communicated in the same
> >> >> way. E.g., v4-only connection syncs still use the same message format,
> >> >> but once you use v6 entries, an unused flag or the 'reserved' field in
> >> >> ip_vs_sync_conn is used. A v6 message would still confuse an older
> >> >> kernel then, but a user would already notice that ipvsadm can't
> >> >> configure the v6 services on the older kernel, so that's not too bad.
> >> >
> >> > If that's a problem, we can easily change the communication port and even
> >> > completely redesign the protocol this way, without having old kernels
> >> > getting confused about the data they get. We might lose the ability to
> >> > sync between different versions, but in the end this is just the
> >> > connection synchronziation and both systems should be running the same
> >> > version. We could also keep the old communication port for some time, if
> >> > that's really needed.
> >>
> >> Yes, starting from scratch on another port sounds like a good idea.
> >> Losing sync ability totally isn't as bad as confusing an older kernel
> >> with new messages, so I hope it's not necessary to keep the old
> >> baggage around?
> >
> > That does sound like a nice idea. I think that is important that we don't
> > confuse older kernels. I guess the only time that ineroperability would be
> > important is when upgrading kernels, where you might want to take the
> > master ldirector down to upgrade it, then the standby.
> Good, that makes two votes for not keeping the old protocol in parallel? ;)

I'd like to keep compatibility if possible. But I think there is
a treshold of pain that we shouldn't cross. 

> >> Is there enough motivation for doing this though before having a
> >> cleaned-up minimal v6 version without the sync daemon? This is where
> >> I'm currently a bit stuck with... any help is appreciated :)
> >
> > IPv6 without sync is fine by me. Its certainly much better than no IPv6.
> > Lets tackle sync a bit later.
> Ok, going for cleaning up and reworking more of the current IPv6 code then...

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