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: Wed, 27 Aug 2008 16:09:44 +1000
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.

> 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.

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