Re: [mpls] OT (was Re: draft-ietf-mpls-in-udp was RE: gre-in-udp draft (


I agree the paper is now obsolete.

Stewart


On 14/01/2014 17:06, Curtis Villamizar wrote:

Lloyd,

Maybe you should reread the paper too before citing it as evidence.
Check the date on it. Check the cited causes of errors.

Packet traces from 1998 and 1999 are prehaps not so relevante today,
particularly wrt error rates due to hosts, router memories, and link
error rates. Look at the cited caused of errors and realize that many
things have changed.

The largest single error in the paper (paerhaps as high as 99.9% of
the errors) was the ACK-of-FIN bug in Windows NT. They may have fixed
that by now. Other large causes were host hardware and host software
bugs (sent bad data in the first place).

One fifth of campus errors were caused by two hosts. This is cited as
a bug in Mac OS on Powermac 8100, fixed at the time of publication.

A lot of host software errors are discussed, where the checksums are
sent bad and therefore will pass any router link FCS.

Sending host hardware errors were thought to be in large part caused
by no data integrity check on host DMA transfers. I think progress
has been made on that front. You can check PCIe. It has a 32bit CRC
per lane in the link layer and retransmits on error.

Router memory errors was thought to play a large role in the non-host
part of the error rate in the paper. Routers use ECC now. Going that
far back they didn't always have parity RAM (and sometimes ran parity
disabled to avoid parity error reloads).

VJHC software errors? Anyone still use VJHC? Those errors should be
gone.

IP over HDLC over T1 missed a few errors at the link layer in those
days. That could be true and occurances dependent on the providers.
In the paper that was thought to be a very small contributor.

Both HDLC and PPP had an option for 16 bit or 32 bit FCS. Often 16
bit was used. Some HDLC equipment could be and was configured to
count errors and send the packets on their way on the assumption that
it was better to count errors and deliver bad packets rather than
deliver no packet. Perhaps also to hide packet loss. Today all of
the link layers in use have 32 bit FCS and count and toss errored
packets. In most equipment all of the memories have ECC and all of
the buses ECC or FCS if serialized.

It is now 14 years since that paper was published in Signcomm and 16
years since some of the observations. Things have changed. Nice bit
of nostangia but that paper may no longer be relevant.

Curtis

reference -
http://conferences.sigcomm.org/sigcomm/2000/conf/paper/sigcomm2000-9-1.pdf

In message
<290E20B455C66743BE178C5C84F1240847E63346BD(_at_)EXMB01CMS(_dot_)surrey(_dot_)ac(_dot_)uk>
l(_dot_)wood(_at_)surrey(_dot_)ac(_dot_)uk writes:

Curtis

I suggest reading Stone's work, particularly

''When The CRC and TCP Checksum Disagree'
for discussion of corruption.

Particularly its conclusions: 'In the internet, that means

we are sending large volumes of incorrect data without
anyone noticing'.

The Layer-2 check is per link, not end-to-end. That matters.The MPLS assumption is that it crosses a link with a frame

checksum. Putting MPLS over UDP breaks that assumption.

Lloyd Wood

http://about.me/lloydwood
________________________________________
From: Curtis Villamizar [curtis(_at_)ipv6(_dot_)occnc(_dot_)com]
Sent: 12 January 2014 18:09
To: Wood L  Dr (Electronic Eng)
Cc: adrian(_at_)olddog(_dot_)co(_dot_)uk; randy(_at_)psg(_dot_)com; 
gorry(_at_)erg(_dot_)abdn(_dot_)ac(_dot_)uk; mpls(_at_)ietf(_dot_)org; 
lisp(_at_)ietf(_dot_)org; ietf(_at_)ietf(_dot_)org; 
david(_dot_)black(_at_)emc(_dot_)com; jnc(_at_)mit(_dot_)edu; 
tsvwg(_at_)ietf(_dot_)org
Subject: Re: [mpls] draft-ietf-mpls-in-udp was RE: gre-in-udp draft (was: RE: 
[tsvwg] Milestones changed for tsvwg WG)

In message <290E20B455C66743BE178C5C84F1240847E63346BA(_at_)EXMB01CMS(_dot_)surrey(_dot_)ac(_dot_)uk>

l(_dot_)wood(_at_)surrey(_dot_)ac(_dot_)uk writes:

On nested checksums, the question is how they are nested; it's a matter
of scope. With a bunch of checksums checking only a payload and any
inner checksums like Russian Matryoshka dolls, the end-to-end argument
tells us that for reliable receipt of the payload, only the innermost checksum
matters.

But here, we are not solely checking the payload, but information on how to
deliver and identify that payload - and while an outer Ethernet CRC is across
the last link, the UDP checksum, though weak, provides a check on the IP
addresses and UDP ports (via the  pseudoheader check) and MPLS stack
from UDP/IP source to UDP/IP destination (and the payload, which is the bit
everyone focuses on as the performance hit as redundant and a processing
cost when the payload has its own check, and the bit that UDP-Lite can leave 
out).

Nothing else checks that scope. The scope is wider, and affects the network
as a whole. Errors in these unchecked fields lead to misdirection and lead to
misdelivery. Or pollution of other ports.

The MPLS assumption is that it's protected and checked by a strong link CRC like
Ethernet, and checked/regenerated by stack processing between hops; here,
in a path context, with zero UDP checksums MPLS has no checking at all.

That UDP would be running over IP over Ethernet or POS or GFP or ...There is no layer-2 currently in use that does not have a robust FCS,

generally a 32 FCS and therefore the MPLS assumption of checking at a
lower layer is still valid.

Curtis

"consequences for cheap hardware and for software implementations"

I'm sorry, when was MPLS cheap?

Lloyd Wood
http://about.me/lloydwood
________________________________________
From: Adrian Farrel [adrian(_at_)olddog(_dot_)co(_dot_)uk]
Sent: 09 January 2014 10:21
To: Wood L  Dr (Electronic Eng); randy(_at_)psg(_dot_)com
Cc: gorry(_at_)erg(_dot_)abdn(_dot_)ac(_dot_)uk; mpls(_at_)ietf(_dot_)org; 
ietf(_at_)ietf(_dot_)org; david(_dot_)black(_at_)emc(_dot_)com; 
tsvwg(_at_)ietf(_dot_)org; jnc(_at_)mit(_dot_)edu; lisp(_at_)ietf(_dot_)org
Subject: RE: [mpls] draft-ietf-mpls-in-udp was RE: gre-in-udp draft (was: RE: 
[tsvwg] Milestones changed for tsvwg WG)

Lloyd and Randy,

With respect to draft-ietf-mpls-in-udp, this is why we have IETF last calls, so
thanks for the comments.

We did take the precaution of sending this I-D for an early TSV Directorate
review because of the concern about a number of factors and the overlap with
tsvwg work, but the review came back "clean". Of course, such a review is just
one person, so this conversation is good.

Wrt zero checksum, where do you stand on nested checksums? There is some claim
that they represent a waste of processing. I am not convinced by that when each
layer is using dedicated hardware (that can presumably process checksums at line
speed), but I am interested in the consequences for cheap hardware and for
software implementations (as have been claimed to be some of the motivations for
this work).

Other TSV-related issues that surely pop up are:
- allocation of ports for foo-in-UDP
- congestion control

Please note that there are a number of I-Ds that you missed in your broad sweep
of "I am opposed". You should probably look at the NVGRE and VXLAN work (which I
think is lurking around the NVO3 working group) because that is also looking at
UDP encaps of a tunnelling protocol.

Thanks,
Adrian

Health warnings:
I am responsible AD for draft-ietf-mpls-in-udp
I am a co-author of the gre-in-udp draft.

-----Original Message-----
From: mpls [mailto:mpls-bounces(_at_)ietf(_dot_)org] On Behalf Of 
l(_dot_)wood(_at_)surrey(_dot_)ac(_dot_)uk
Sent: 09 January 2014 08:07
To: randy(_at_)psg(_dot_)com
Cc: gorry(_at_)erg(_dot_)abdn(_dot_)ac(_dot_)uk; mpls(_at_)ietf(_dot_)org; 
ietf(_at_)ietf(_dot_)org; david(_dot_)black(_at_)emc(_dot_)com;
tsvwg(_at_)ietf(_dot_)org; jnc(_at_)mit(_dot_)edu; lisp(_at_)ietf(_dot_)org
Subject: Re: [mpls] draft-ietf-mpls-in-udp was RE: gre-in-udp draft (was: RE:
[tsvwg] Milestones changed for tsvwg WG)

Randy,

okay, let  tsvwg adopt draft-yong-tsvwg-gre-in-udp-encap, and let's get
consensus on  it. And then the authors can adopt that consensus for

mpls-in-udp,

which overlaps in authorship...

thanks,

Lloyd Wood
http://about.me/lloydwood
________________________________________
From: Randy Bush [randy(_at_)psg(_dot_)com]
Sent: 09 January 2014 07:51
To: Wood L  Dr (Electronic Eng)
Cc: david(_dot_)black(_at_)emc(_dot_)com; 
gorry(_at_)erg(_dot_)abdn(_dot_)ac(_dot_)uk; ietf(_at_)ietf(_dot_)org; 
mpls(_at_)ietf(_dot_)org;
jnc(_at_)mit(_dot_)edu; lisp(_at_)ietf(_dot_)org; tsvwg(_at_)ietf(_dot_)org
Subject: Re: draft-ietf-mpls-in-udp was RE: gre-in-udp draft (was: RE: [tsvwg]
Milestones changed for tsvwg WG)

Because they specify zero UDP checksums,
I oppose publication of draft-ietf-mpls-in-udp in its current form
I oppose tsvwg adoption of draft-yong-tsvwg-gre-in-udp-encap in its current

form.

I oppose the IETF lisp documents.

lloyd,

i think i understand your position.  but i disagree with preventing wg
adoption of draft-yong-tsvwg-gre-in-udp-encap, mainly because i strongly
see wg adoption as how we get to discuss and work on a document, not as
approval of the document.  as david said, i think we need to discuss it
so we can decide if it should be fixed.  to do so, we have to adopt it.

randy

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Re: [mpls] OT (was Re: draft-ietf-mpls-in-udp was RE: gre-in-udp draft (was: RE: [tsvwg] Milestones changed for tsvwg WG))