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

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Date:	Fri, 22 Aug 2008 14:14:11 +0200
From:	"Julius Volz" <juliusv@...gle.com>
To:	"Sven Wegener" <sven.wegener@...aler.net>
Cc:	"Graeme Fowler" <graeme@...emef.net>,
	"Simon Horman" <horms@...ge.net.au>, netdev@...r.kernel.org,
	lvs-devel@...r.kernel.org, kaber@...sh.net, vbusam@...gle.com
Subject: Re: [PATCH RFC 00/24] IPVS: Add first IPv6 support to IPVS

On Fri, Aug 22, 2008 at 1:23 PM, Sven Wegener <sven.wegener@...aler.net> 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?

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 :)

Julius

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