Tom,
> Why would someone put six segments in a parcel if they already have a
9K link MTU?
> Why not just send one segment in 9K?
This is the mindset that we need to overcome. We have had it drilled
into our heads
that MSS must be the same as the path MTU, but it does not need to be
that way.
If the MSS is smaller than the path MTU, but we can send multiple
segments in a
single parcel that more closely approaches the size of the path MTU then
amortization savings are possible.
>The algorithm isn't the problem, it's supporting new protocols and multiple
>checksums in a packet in hardware.
But Tom, how hard can this be? Instead of running the Internet
checksum 1 time
over N octets of data simply run it M times over N/M octet chunks of
the data in
succession but still in a single pass. You spoke before of NICs
adapting to support
TCP jumbograms – if they can do that, why not a very straightforward
application
of Internet checksum? I haven’t looked at this in a long while, but
isn’t this also
similar to what UDP-lite did?
> Either you're trivializing reassembly or maybe you're thinking of
some new method that
> somehow avoids all the pitfalls and problems we've had with
reassembly over the years!
Intermediate node parcel reassembly is really just an optimization to
try to pass the
largest possible parcels on to the next hop instead of passing many
smaller ones. It is
really just a concatenation of segments of sub-parcels belonging to
the same original
parcel. Reordering is unimportant – it is OK to concatenate
sub-parcels 3,8,5,2 in that
order and without even waiting for any other sub-parcels to show up.
The application
will simply perceive it as a case of network reordering and the upper
layer protocol
will do the correct thing with the sequence numbers. AFAICT, the only
hard requirement
is that the final sub-parcel must not be concatenated as an
intermediate sub-parcel.
This stuff will all work, and it will work for the betterment of the
Internet.
Fred
*From:*Tom Herbert [mailto:t...@herbertland.com]
*Sent:* Monday, July 11, 2022 2:57 PM
*To:* Templin (US), Fred L <fred.l.temp...@boeing.com>
*Cc:* Richard Li <richard...@futurewei.com>; Juan Carlos Zuniga
(juzuniga) <juzuniga=40cisco....@dmarc.ietf.org>; int-area@ietf.org
*Subject:* Re: [EXTERNAL] Re: [Int-area] Call for WG adoption of
draft-templin-intarea-parcels-10
EXT email: be mindful of links/attachments.
On Mon, Jul 11, 2022 at 2:20 PM Templin (US), Fred L
<fred.l.temp...@boeing.com> wrote:
Tom, some rejoinders:
>Yes, I agree if the packet is fragmented by the network then this is a
nice feature.
>However, today we already have this from a host perspective property by
just
>sending "small" packets.
It can be readily shown that some applications get much greater
performance by
sending larger packets that trigger fragmentation/reassembly than
by sending
smaller packets that do not. Multiple order of magnitude
performance increases
are indeed possible.
>I'm not sure the savings qualify as significant. 9K MTUs are becoming
common in data centers
>and the standard TCP/IPv6 header is 80 bytes so that's already less
than 1% overhead.
I think 9K is only a starting point, and IP parcels pave the way
to much larger link MTUs,
possibly even in excess of 64KB. And, doing the math, even for
just a 9K link sending a
single parcel that contains 6x 1440 octet segments would save 5 *
60 == 300 octets in
Why would someone put six segments in a parcel if they already have a
9K link MTU? Why not just send one segment in 9K?
comparison with sending 6x 1500 octet packets with 60 octets of
IP/TCP headers per
packet. For links with larger MTUs, the savings for sending
parcels with lots of segments
(up to 64) becomes even greater.
>As I already mentioned, this is addressed by the BiGTCP work
(https://lwn.net/Articles/884104).
>Sending or receiving multi-megabytes TCP segments in one system call is
now feasible. Also, it's
>inevitable that NIC vendors will apply this also to be able to offload TCP
jumbo grams. Given this
>is just software that doesn't require hardware change or on-the-wire
protocols to change, it's
>immediately deployable with just a softwar change which is a huge benefit
to
datacenter operators.
As I have said, IP parcels has the same advantage within the host
system-call (user-space
to kernel-space) context. But, IP parcels goes a step further to
provide efficient packaging
over-the-wire, whereas the approach you are referring to opens the
box inside the
kernel and sends individual packets instead of aggregates.
>All modern NIC HW can deal with offloading a single checksum per
packet, it's going to be
>a major effort for them to offload multiple checksum like IP
parcels needs. Without checksum
>offload, this would be a non-starter for a lot of deployments.
Check the latest spec (now at -12 and likely to stay that way
until IETF114. Any H/W checksum
that can run over the first segment of a packet should be possible
to make run over the N-1
additional segments of the same packet (parcel) by applying the
very familiar Internet
checksum algorithm.
The algorithm isn't the problem, it's supporting new protocols and
multiple checksums in a packet in hardware.
>I'm not convinced of that. For instance, I'm skeptical that
intermediate devices trying to reassemble
>packets that aren't addressed to themselves could ever be robust or
efficient (i.e. complexity, non-work
>conserving resource requirements, security issues with reassembly,
multi-path that causes latency
>increase, potential DoS vector, etc.). Can you comment on this?
Perhaps what is confusing this matter is that the intermediate
devices referred to
here most certainly do not refer to all routers in the path.
Instead, what is intended
here is an OMNI intermediate device, of which there may be
something on the order
of 0, 1, or 2 of them on the path between the OMNI source and
destination even
though there may be many 10’s or even 100’s of ordinary IP routers
on the path.
And, again, this is not a strict reassembly case – instead, it is
an opportunistic
“combine if convenient; else forward” swift decision.
Either you're trivializing reassembly or maybe you're thinking of some
new method that somehow avoids all the pitfalls and problems we've had
with reassembly over the years! Consider that many NIC vendors have
tried, and largely failed, to get any sort of device reassembly widely
deployed (e.g. IP reassembly, TCP segmentation reassembly, etc.). The
reason they failed is because they can't give the host stack
transparency and control over the reassembly process.
In its nature reassembly can only be done with at least packets. That
means a device performing reassembly has to receive one packet, hold
it, and wait for the following packet to perform reassembly. That
makes reassembly, unlike fragmentation, a non-work conserving process.
Many issues and policies arise from this. For instance, what happens
if a packet is held and the following packet is never seen? (usually
implies a reassembly timer). What happens if a packet is received OOO
and is already forwarded, but the preceding packet is then received,
do we try to reassemble that one? (the solution here seems to be to
maintain some sort of flow state)? What about overlapping fragments
and the security issues around that?
IMO, if the WG does pursue this, I believe a lot of the effort will be
in specifying how reassembly in intermediate nodes works.
Tom
Thanks - Fred
*From:*Tom Herbert [mailto:t...@herbertland.com]
*Sent:* Monday, July 11, 2022 1:34 PM
*To:* Templin (US), Fred L <fred.l.temp...@boeing.com>
*Cc:* Richard Li <richard...@futurewei.com>; Juan Carlos Zuniga
(juzuniga) <juzuniga=40cisco....@dmarc.ietf.org>; int-area@ietf.org
*Subject:* [EXTERNAL] Re: [Int-area] Call for WG adoption of
draft-templin-intarea-parcels-10
EXT email: be mindful of links/attachments.
On Mon, Jul 11, 2022 at 12:22 PM Templin (US), Fred L
<fred.l.temp...@boeing.com> wrote:
Richard and others, thank you for these comments and for the
ensuing discussion that
took place over the time I was away on vacation. Strange how
the timing hit when I
was away from the office and off the grid - I was on a camping
trip in Canada not far
from where Steve Deering lives although I did not visit him.
In any event, I was able to push out a new draft version ahead
of the deadline that
may address some (but likely not all) of your concerns:
https://datatracker.ietf.org/doc/draft-templin-intarea-parcels/
The major change is that the draft now talks about
interactions with upper layer
protocols including TCP and UDP, whereas the previous draft
versions were silent
regarding upper layer protocol framing.
To others who have commented, I beg to differ and maintain
that IP parcels do
represent a significant improvement over the current state of
affairs and over
just regular IP jumbograms. In particular:
Hi Fred, some comments in line.
1) IP parcels make it so that the loss unit is a single
segment instead of the entire
packet/parcel, and loss of a segment often results in
retransmission of just that
segment instead of the entire packet/parcel.
Yes, I agree if the packet is fragmented by the network then this
is a nice feature. However, today we already have this from a host
perspective property by just sending "small" packets.
2) IP parcels are more efficient than sending a single segment
per IP packet, since
the parcel includes a single IP header plus single full
{TCP,UDP} header for possibly
many segments. This can result in significant savings in terms
of bits over the wire
for omitting unnecessary header bytes.
I'm not sure the savings qualify as significant. 9K MTUs are
becoming common in data centers and the standard TCP/IPv6 header
is 80 bytes so that's already less than 1% overhead.
Consider the postal service analogy; when
many items can be sent together in a single package/parcel
there is a large savings
in shippeing and handling costs than when each individual item
is shipped separately.
As I already mentioned, this is addressed by the BiGTCP work
(https://lwn.net/Articles/884104). Sending or receiving
multi-megabytes TCP segments in one system call is now feasible.
Also, it's inevitable that NIC vendors will apply this also to be
able to offload TCP jumbo grams. Given this is just software that
doesn't require hardware change or on-the-wire protocols to
change, it's immediately deployable with just a softwar change
which is a huge benefit to datacenter operators.
3) IP parcels improve large packet integrity by including a
separate checksum for
each segment instead of a single checksum for the entire packet.
All modern NIC HW can deal with offloading a single checksum per
packet, it's going to be a major effort for them to offload
multiple checksum like IP parcels needs. Without checksum offload,
this would be a non-starter for a lot of deployments.
This means that
large parcels (up to a few MB) can be sent in one piece over
links with sufficiently
large MTU without requiring the link itself to provide strong
integrity checks over
the entire length of the parcel. This means that link MTUs
significantly larger than
9KB are now safely possible.
4) IP parcels offer all of the efficiency advantages to upper
layers as are offered
by GSO/GRO, etc. but also provide benefits 1) through 3) above
that are not
offered by GSO/GRO.
Most of this is doable in GSO/GRO.
5) Plus, the idea is just plain neat. Better packaging is
good. More efficient
handling is good. Reduced header overhead is good. SAFE larger
MTUs are
good. The idea itself is good.
I'm not convinced of that. For instance, I'm skeptical that
intermediate devices trying to reassemble packets that aren't
addressed to themselves could ever be robust or efficient (i.e.
complexity, non-work conserving resource requirements, security
issues with reassembly, multi-path that causes latency increase,
potential DoS vector, etc.). Can you comment on this?
Tom
Fred
*From:*Int-area [mailto:int-area-boun...@ietf.org] *On Behalf
Of *Richard Li
*Sent:* Friday, July 01, 2022 3:11 PM
*To:* Juan Carlos Zuniga (juzuniga)
<juzuniga=40cisco....@dmarc.ietf.org>
*Cc:* int-area@ietf.org
*Subject:* Re: [Int-area] Call for WG adoption of
draft-templin-intarea-parcels-10
Chairs and Authors,
I always like every new idea and effort to improve the
Internet performance, and thus I have read this draft with a
great interest. The following are my
observations/comments/questions. If they don’t make any sense
to you, please accept my apology, and disregard them.
1.The text “multiple upper layer protocol segments” is
ambiguous. It seems that you really mean “multiple segments
from ‘the same’ upper layer protocol”, doesn’t it? It seems
that multiple segments from different upper layer protocols
are not allowed in your parcel.
2.Is the following a fair statement? All segments in the same
packet come from the same application identified by the 5-tupe
(source address, destination address, source port, destination
port, protocol number).
3.Segment size
You require that their sizes be the same except for the last
one. Is this required for easy implementation or what? Do you
require it for any other reasons?
4.TTL issue
You described how parcels are forwarded over the Internetwork,
and in particular you described what the ingress/egress
middlebox does about parcels. I understand that the ingress
middlebox may break the parcel into smaller ones, which may
rejoin at the egress middlebox. My question is about TTL. As
different smaller parcels may traverse along different paths,
as a result their TTLs may be different when they reach the
egress middlebox . How does the egress middlebox set up the
TTL value? Please provide more descriptions.
5.Reordering at the egress middlebox
The parcels would arrive one after another, and therefore the
egress middlebox would “wait” for a little bit to identify and
pick up enough parcels/packets for their rejoining and
repackaging. A description of the egress middlebox behavior
would be useful and helpful, in particular I would like to
know more about the waiting time if any, and how you deal with
the reordering and loss.
6.IPv4 option
Does IETF still allow to change/add IPv4 option fields? I
might be wrong, but aren’t they frozen? Also, do commercial
routers still care about IPv4 options?
7.IPv6 option
This draft has defined a hop-by-hop option, it will require
every intermediate IPv6 router to inspect this option. There
have been some discussions on the pros/cons about Hop-by-Hop
IPv6 Option. Is there any feedback from WG 6man?
8.Parcel Path Qualification
This draft has described a method for parcel path
qualification probe from end to end. It is nice to have it,
but it is unreliable simply for the following reason: a probe
parcel goes along one specific path, and your real application
parcels may take different paths.
9.Integrity
First paragraph of Section 7. More explanation/elaboration
should be useful. I might have missed it in previous
paragraphs, but if I do, please provide a reference to it such
as “as described in …”.
10.Implementation Status
In section 10. TSO’s performance gain and Parcel’s gain should
be regarded as two different things. Since this draft is
adding a hop-by-hop option, every intermediate router is
required to process the hop-by-hop option, which will,
theoretically speaking, lead to performance downgrade. Of
course, the whole performance would depend on many other
factors, such as the total numbers of routing table lookups
and number of segments.
11.General observation
This proposal essentially tries to solve a problem caused by
MTU. If MTU be very big, one would simply put the whole data
in a single packet. Since MTU is limited, a packet has to be
cut into many smaller pieces (segments). In the existing
specification, when an intermediate router sees a packet with
its size larger than MTU, the router would be expected to
fragment it so that the fragments could be forwarded. Here let
me call it “fragmentation as needed”. In reality, however,
some (if not all) commercial routers don’t do “fragmentation
as needed”, instead of fragmenting the packet they simply
discard it in order to achieve the wire-speed. This draft
defines a new way to address the MTU issue: when a router sees
a packet with its size larger than MTU, the router is asked to
fragment it in a prescribed way (fragment it into pre-packaged
segments). If I may, let me call it “fragmentation as
prescribed”. Both “fragmentation as needed” and “fragmentation
as prescribed” would require the support from intermediate
routers. As the same as fragmentation as needed, fragmentation
as prescribed may downgrade the performance of intermediate
routers. What is more, intermediate routers/boxes may perform
“rejoining and repackaging”, which will adversely impact the
performance of the intermediate routers/boxes.
Best regards,
Richard
*From:*Int-area <int-area-boun...@ietf.org> *On Behalf Of
*Juan Carlos Zuniga (juzuniga)
*Sent:* Wednesday, June 22, 2022 12:25 PM
*To:* int-area@ietf.org
*Subject:* [Int-area] Call for WG adoption of
draft-templin-intarea-parcels-10
Dear IntArea WG,
We are starting a 2-week call for adoption of the IP-Parcels
draft:
https://www.ietf.org/archive/id/draft-templin-intarea-parcels-10.html
<https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-templin-intarea-parcels-10.html&data=05%7C01%7Crichard.li%40futurewei.com%7C715b5db213134932c70208da5484f702%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C1%7C637915227299598680%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000%7C%7C%7C&sdata=w4G5ypaSRv%2FR31%2F%2B857XT2xUqHdEXv90ubD5GGjqBEQ%3D&reserved=0>
The document has been discussed for some time and it has
received multiple comments.
If you have an opinion on whether this document should be
adopted by the IntArea WG please indicate it on the list by
the end of Wednesday July 6^th .
Thanks,
Juan-Carlos & Wassim
(IntArea WG chairs)
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