Message-ID: <20090429115716.3e315812@nehalam>
Date:	Wed, 29 Apr 2009 11:57:16 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Mark Smith 
	<lnx-netdev@...22607b6285f9c5d5ea31ea9d8a7ac.nosense.org>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC, PATCH 2.6.29.2] Ethernet V2.0 Configuration Testing
 Protocol, revision 20090428

On Wed, 29 Apr 2009 21:04:36 +0930
Mark Smith <lnx-netdev@...22607b6285f9c5d5ea31ea9d8a7ac.nosense.org> wrote:

> Hi Stephen,
> 
> Thanks for you time.
> 
> On Tue, 28 Apr 2009 16:15:45 -0700
> Stephen Hemminger <shemminger@...tta.com> wrote:
> 
> > On Tue, 28 Apr 2009 22:01:43 +0930
> > Mark Smith  <lnx-netdev@...22607b6285f9c5d5ea31ea9d8a7ac.nosense.org> wrote:
> > 
> > > Hi,
> > > 
> > > Following on from my initial ECTP post on the 23rd of April, here is an
> > > updated revision.
> > > 
> > > Changes:
> > > 
> <snip>
> 
> > > 
> > > Feedback from some networking and sys admin people I've told about it
> > > has been positive - they all agree with the benefit of being able to
> > > perform "ping" style testing on an Ethernet segment without requiring
> > > IP to be configured.
> > > 
> > > Any suggestions for improvement would be most appreciated.
> > > 
> > > Thanks very much,
> > > Mark.
> > > 
> > 
> > Why does this have to be in the kernel?  Why not all in user space
> > with AF_PACKET?
> 
> It doesn't have to be, however I think the same question could be asked
> as to why the IPv4, IPv6 and 802.2/LLC echo reply functions are in the
> kernel, when they could be implemented in user space too.
> 
> Here are the reasons why I think it should be in the kernel:
> 
> o  As the Ethernet V2.0 protocol is implemented in the kernel, the
> offical Ethernet V2.0 testing function should also be implemented in
> the kernel. Making Ethernet layer testing rely on a user space
> process makes it less reliable and less universally available as a
> specific test of Ethernet link layer connectivity. IIRC, this is the
> justification for why IPv4 and IPv6 ICMP echo reply functions are in
> operating system kernels rather than as user space processes. 

RSTP is implemented in user-space (IEEE 802.1d) and other standard
protocols as well. This reason is invald.

> o  Compared to near equivalent link tesing using IPv4 ping, ECTP doesn't
> require any pre-configuration at all.

Doing it in userspace would not require configuration either and could
be more flexible. It would work better with existing infrastructure
firewalling, rate limiting, ...

> o  I think it can serve as a "hello world"-like example of basic packet
> processing in the kernel. Other protocols that exist in the kernel that
> can be used as examples are pretty complicated when compared to ECTP.
> To understand their implementations, you need to understand the protocol
> well before hand, which can be a fairly time consuming task. As ECTP is
> a very simple, single packet format protocol, that has pretty simple
> processing, the time investment in understanding it is fairly small -
> probably well and truly less than an hour. I think that, combined with
> what I hope is a very straight forward and easy to follow
> implementation, could help people come quickly up to speed with the
> basics of kernel packet processing. It's for this reason that I also 
> invested quite a bit of time in providing an overview of the protocol
> in the Documentation/networking/ectp.txt file. I think it also could be
> a simple to follow example of how to use SKB queues, and how to use the
> new high res timers subsystem.

Example code, doesn't necessarily have to be shipped code.

> o  It would be another method for testing network stack latency. The
> recent udpping testing that is being performed by Christoph Lameter is
> testing the Ethernet, IP and UDP layers of the kernel. Using ECTP for
> this type of testing isolates the IP and UDP implementations from
> influencing the results.

This reason does make sense, but the latency of ethernet driver
is probably greater than userspace overhead

 
> o  It provides more link layer testing capabilities than the 802.2/LLC
> TEST function. ECTP supports querying of available ECTP nodes via
> broadcast and multicast requests, and testing of paths between
> a number of stations. The 802.2/LLC TEST function only supports
> request / reply testing between a pair of stations.


But can it be firewalled?
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