tinc devel - Dec 2014 - tinc vpn: adding dscp passthrough (priorityinherit), ecn, and fq_codel support

I have long included tinc in the cerowrt project as a lighter weight,
meshy alternative to conventional vpns.

I sat down a few days ago to think about how to make vpn connections
work better through fq_codel, and decided I should maybe hack on a vpn
to do the job. So I picked up tinc's source code for the first time,
got it working on IPv6 as a switch in a matter of minutes between two
endpoints (very impressed, thx!), and started hacking at it to see
where I would get.

This is partially the outgrowth of looking at an ietf document on ecn
encapsulation and vpns....

https://tools.ietf.org/html/rfc6040

Experimental patches so far are at:

https://github.com/dtaht/tinc

I successfully converted tinc to use sendmsg and recvmsg, acquire (at
least on linux) the TTL/Hoplimit and IP_TOS/IPv6_TCLASS packet fields,
as well as SO_TIMESTAMPNS, and use a higher resolution internal clock.
Got passing through the dscp values to work also, but:

A) encapsulation of ecn capable marked packets, and availability in
the outer header, without correct decapsulationm doesn't work well.

The outer packet gets marked, but by default the marking doesn't make
it back into the inner packet when decoded.

see:

http://snapon.lab.bufferbloat.net/~d/tinc/ecn.png # packets get marked
but not decapsulated - and never dropped so they
just keep accumulating delay over this path....

vs

http://snapon.lab.bufferbloat.net/~d/tinc/noecn.png

So communicating somehow that a path can take ecn (and/or diffserv
markings) is needed between tinc daemons. I thought of perhaps
crafting a special icmp message marked with CE but am open to ideas
that would be backward compatible.

It IS nice to be able to operate with near zero packet loss.....

B) I have long theorized that a lot of userspace vpns bottleneck on
the read and encapsulate step, and being strict FIFOs,
gradually accumulate delay until finally they run out of read socket
buffer space and start dropping packets.

so I had a couple thoughts towards using multiple rx queues in the
vtun interface, and/or trying to read more than one packet at a time
(via recvmmsg) and do some level of fair queueing and queue management
(codel) inside tinc itself. I think that's
pretty doable without modifying the protocol any, but I'm not sure of
it's value until I saturate some cpu more. (and if you thought recvmsg
was complex, look at recvmmsg)

C) Moving forward, in this case, it looks like I am bottlenecked on my
gateway anyway (only eating 36% of cpu at this speed,
not showing any substantial delays with SO_TIMESTAMPNS (but I haven't
fully checked that)

http://snapon.lab.bufferbloat.net/~d/tinc2/native_ipv6.png

http://snapon.lab.bufferbloat.net/~d/tinc2/tunneled_classified.png

I am a little puzzled as to how well tinc handles out of order packet
delivery (the EF,BE,BK(CS1) diffserv queues are handled differently by
the shaper on the gateway...

and:

D)

the bottleneck link above is actually not tinc but the gateway, and as
the gateway reverts to codel behavior on a single encapsulated flow
encapsulating all the other flows, we end up with about 40ms of
induced delay on this test. While I have a better codel (gets below
20ms latency, not deployed), *fq*_codel by identifying individual
flows gets the induced delay on those flows down below 5ms.

At one level, tinc being so nicely meshy means that the "fq" part of
fq_codel on the gateway will have more chance to work against the
multiple vpn flows it generates for all the potential vpn endpoints...

but at another... lookie here! ipv6! 2^64 addresses or more to use!
and port space to burn! What if I could make tinc open up 1024 ports
per connection, and have it fq all it's flows over those? What could
go wrong?




-- 
Dave T?ht

http://www.bufferbloat.net

On Wed, Dec 03, 2014 at 12:07:59AM -0800, Dave Taht wrote:

[...]
> https://github.com/dtaht/tinc
> 
> I successfully converted tinc to use sendmsg and recvmsg, acquire (at
> least on linux) the TTL/Hoplimit and IP_TOS/IPv6_TCLASS packet fields,
Windows does not have sendmsg()/recvmsg(), but the BSDs support it.
> as well as SO_TIMESTAMPNS, and use a higher resolution internal clock.
> Got passing through the dscp values to work also, but:
> 
> A) encapsulation of ecn capable marked packets, and availability in
> the outer header, without correct decapsulationm doesn't work well.
> 
> The outer packet gets marked, but by default the marking doesn't make
> it back into the inner packet when decoded.
Is the kernel stripping the ECN bits provided by userspace? In the code
in your git branch you strip the ECN bits out yourself.
> So communicating somehow that a path can take ecn (and/or diffserv
> markings) is needed between tinc daemons. I thought of perhaps
> crafting a special icmp message marked with CE but am open to ideas
> that would be backward compatible.
PMTU probes are used to discover whether UDP works and how big the path
MTU is, maybe it could be used to discover whether ECN works as well?
Set one of the ECN bits on some of the PMTU probes, and if you receive a
probe with that ECN bit set, also set it on the probe reply. If you
succesfully receive a reply with ECN bits set, then you know ECN works.
Since the remote side just echoes the contents of the probe, you could
also put a copy of the ECN bits in the probe payload, and then you can
detect if the ECN bits got zeroed. You can also define an OPTION_ECN in
src/connection.h, so nodes can announce their support for ECN, but that
should not be necessary I think.
> B) I have long theorized that a lot of userspace vpns bottleneck on
> the read and encapsulate step, and being strict FIFOs,
> gradually accumulate delay until finally they run out of read socket
> buffer space and start dropping packets.
Well, encryption and decryption takes a lot of CPU time, but context
switches are also bad.

Tinc is treating UDP in a strictly FIFO way, but actually it does use a
RED algorithm when tunneling over TCP. That said, it only looks at its
own buffers to determine when to drop packets, and those only come into
play once the kernel's TCP buffers are filled.
> so I had a couple thoughts towards using multiple rx queues in the
> vtun interface, and/or trying to read more than one packet at a time
> (via recvmmsg) and do some level of fair queueing and queue management
> (codel) inside tinc itself. I think that's
> pretty doable without modifying the protocol any, but I'm not sure of
> it's value until I saturate some cpu more.
I'd welcome any work in this area :)
> (and if you thought recvmsg was complex, look at recvmmsg)
It seems someone is already working on that, see
https://github.com/jasdeep-hundal/tinc.
> D)
> 
> the bottleneck link above is actually not tinc but the gateway, and as
> the gateway reverts to codel behavior on a single encapsulated flow
> encapsulating all the other flows, we end up with about 40ms of
> induced delay on this test. While I have a better codel (gets below
> 20ms latency, not deployed), *fq*_codel by identifying individual
> flows gets the induced delay on those flows down below 5ms.
But that should improve with ECN if fq_codel is configured to use that,
right?
> At one level, tinc being so nicely meshy means that the "fq" part
of
> fq_codel on the gateway will have more chance to work against the
> multiple vpn flows it generates for all the potential vpn endpoints...
> 
> but at another... lookie here! ipv6! 2^64 addresses or more to use!
> and port space to burn! What if I could make tinc open up 1024 ports
> per connection, and have it fq all it's flows over those? What could
> go wrong?
Right, hash the header of the original packets, and then select a port
or address based on the hash? What about putting that hash in the flow
label of outer packets? Any routers that would actually treat those as
separate flows?

-- 
Met vriendelijke groet / with kind regards,
     Guus Sliepen <guus at tinc-vpn.org>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: Digital signature
URL:
<http://www.tinc-vpn.org/pipermail/tinc-devel/attachments/20141203/4f58c733/attachment.sig>

On Wed, Dec 3, 2014 at 6:17 AM, David P. Reed <dpreed at reed.com>
wrote:
> Tor needs this stuff very badly.
Tor has many, many problematic behaviors relevant to congestion control
in general. Let me paste a bit of private discussion I'd had on it in a
second,
but a very good paper that touched upon it all was:

   DefenestraTor: Throwing out Windows in Tor
   http://www.cypherpunks.ca/~iang/pubs/defenestrator.pdf

Honestly tor needs to move to udp, and hide in all the upcoming
webrtc traffic....

http://blog.mozilla.org/futurereleases/2014/10/16/test-the-new-firefox-hello-webrtc-feature-in-firefox-beta/

webrtc needs some sort of non-centralized rendezvous mechanism, but I am REALLY
happy to see calls and video stay entirely inside my network when they can be
negotiated as such.

https://plus.google.com/u/0/107942175615993706558/posts/M4xUtpCKJ4P

And of course, people are busily reinventing torrent in webrtc without
paying attention to congestion control at all.

https://github.com/feross/webtorrent/issues/39

Giving access to udp to javascript programmers... what could go wrong?
:/
> I do wonder whether we should focus on vpn's rather than end to end
> encryption that does not leak secure information through from inside as the
> plan seems to do.
"plan"?

I like e2e encryption. I also like overlay networks. And meshes.
And working dns and service discovery. And low latency.

vpns are useful abstractions for sharing an address space you
may not want to share more widely.

and: I've taken a lot of flack about how fq doesn't help on conventional
vpns, and well, just came up with an unconventional vpn idea,
that might have some legs here... (certainly in my case tinc
as constructed already, no patches, solves hooking together the
12 networks I have around the globe, mostly)

As for "leaking information", packet size and frequency is generally
an obvious indicator of a given traffic type, some padding added or
no. There is one piece of plaintext
in tinc (the seqno), also. It also uses a fixed port number for  both
sides of the connection (perhaps it shouldn't)

So I don't necessarily see a difference between sending a whole lot of
varying data on one tuple

2001:db8::1 <-> 2001:db8:1::1 on port 655

vs

2001:db8::1 <-> 2001:db8:1::1 port 655
2001:db8::2 <-> 2001:db8:1::1 port 655
2001:db8::3 <-> 2001:db8:1::1 port 655
2001:db8::4 <-> 2001:db8:1::1 port 655
....

which solves the fq problem on a vpn like tinc neatly. A security feature
could be source specific routing where we send stuff over different paths
from different ipv6 source addresses... and mixing up the src/dest ports
more but that complexifies the fq portion of the algo.... my thought
for an initial implementation is to just hard code the ipv6 address range.

I think however that adding tons and tons of ipv6 addresses to a given
interface is probably slow,
and might break things like nd and/or multicast...

what would be cooler would be if you could allocate an entire /64 (or
/118) to the vpn daemon

bindtoaddress(2001:db8::/118) (give me all the data for 1024 ips)

but I am not sure how to go about doing that..

...moving back to a formerly private discussion about tors woes...


"This conversation is a bit separate from #11197 (which is an
implementation issue in obfsproxy), so separate discussion somewhere
would probably be required.

So, there appears to be a slight misconception on how tor traffic
travels across the Internet that I will attempt to clarify, and
hopefully not get too terribly wrong.

Each step of a given connection over tor involves multiple TCP/IP
connections.  To use a standard example of someone trying to watch Cat
Videos on the "real internet", it will look approximately like thus:

   Client <-> Guard <-> Relay <-> Exit <-> Cat Videos

Each step is a separate TCP/IP connection, authenticated and encrypted
via TLS (TLS is likewise terminated at each hop). Using a pluggable
transport encapsulates the first hop's TLS session with a different
protocol be it obfs2, obfs3, or something else.

The cat videos are passed through this path of many TCP/IP connections
across things called Circuits that are created/extended by the Client
one hop at a time (So the example above, the kitty cats travel across
4 TCP/IP connections, relaying data across a Circuit that spans from
the Client to the Exit.  If my art skills were up to it, I would draw a
diagram.).

Circuits are currently required to provide reliable, in-order delivery.

In addition to the standard congestion control provided by TCP/IP on a
per-hop basis, there is Circuit level flow control *and* "end to end"
flow control in the form of RELAY_SENDME cells, but given that multiple
circuits can end up being multiplexed over a singlular TCP/IP
connection, propagation of these RELAY_SENDME cells can get delayed due
to HOL issues.

So, with that quick and dirty overview out of the way:

 * "Ah so if ecn is enabled it can be used?"

   ECN will be used if it is enabled, *but* the congestion information
   will not get propaged to the source/destination of a given stream.

 * "Does it retain iw10 (the Linux default nowadays sadly)?"

   Each TCP/IP connection if sent from a host that uses a obnoxiously
   large initial window, will have an obnoxiously large initial
   window.

It is worth noting that since multiple Circuits originating from
potentially numerous clients can and will reuse existing TCP/IP
connections if able to (see 5.3.1 of the tor spec) that dropping packets
between tor relays is kind of bad, because all of the separate
encapsulated flows sharing the singular TCP/IP link will suffer (ECN
would help here).  This situation is rather unfortunate as the good
active queue management algorithms drop packets (when ECN is not
available).

A better summary of tor's flow control/bufferbloat woes is given in:

   DefenestraTor: Throwing out Windows in Tor
   http://www.cypherpunks.ca/~iang/pubs/defenestrator.pdf

The N23 algorithm suggested in the paper did not end up getting
implemented into Tor, but I do not remember the reason off the top of
my head."

>
>
>
> On Dec 3, 2014, Guus Sliepen <guus at tinc-vpn.org> wrote:
>>
>> On Wed, Dec 03, 2014 at 12:07:59AM -0800, Dave Taht wrote:
>>
>> [...]
>>>
>>> https://github.com/dtaht/tinc
>>>
>>> I successfully converted tinc to use sendmsg and recvmsg, acquire
(at
>>> least on linux) the TTL/Hoplimit and IP_TOS/IPv6_TCLASS packet
fields,
>>
>>
>> Windows does not have sendmsg()/recvmsg(), but the BSDs support it.
>>
>>> as well as SO_TIMESTAMPNS, and use a higher resolution internal
clock.
>>> Got passing through the dscp values to work also, but:
>>>
>>> A) encapsulation of ecn capable marked packets, and availability in
>>> the outer header, without correct decapsulationm doesn't work
well.
>>>
>>> The outer packet gets marked, but by default the marking
doesn't make
>>> it back into the inner packet when decoded.
>>
>>
>> Is the kernel stripping the ECN bits provided by userspace? In the code
>> in your git branch you strip the ECN bits out yourself.
>>
>>> So communicating somehow that a path can take ecn (and/or diffserv
>>> markings) is needed between tinc daemons. I thought of perhaps
>>> crafting a special icmp message marked with CE but am open to ideas
>>> that would be backward compatible.
>>
>>
>> PMTU probes are used to discover whether UDP works and how big the path
>> MTU is, maybe it could be used to discover whether ECN works as well?
>> Set one of the ECN bits on some of the PMTU probes, and if you receive
a
>> probe with that ECN bit set, also set it on the probe reply. If you
>> succesfully receive a reply with ECN bits set, then you know ECN works.
>> Since the remote side just echoes the contents of the probe, you could
>> also put a copy of the ECN bits in the probe payload, and then you can
>> detect if the ECN bits got zeroed. You can also define an OPTION_ECN in
>> src/connection.h, so nodes can announce their support for ECN, but that
>> should not be necessary I think.
>>
>>> B) I have long theorized that a lot of userspace vpns bottleneck on
>>> the read and encapsulate step, and being strict FIFOs,
>>> gradually accumulate delay until finally they run out of read
socket
>>> buffer space and start dropping packets.
>>
>>
>> Well, encryption and decryption takes a lot of CPU time, but context
>> switches are also bad.
>>
>> Tinc is treating UDP in a strictly FIFO way, but actually it does use a
>> RED algorithm when tunneling over TCP. That said, it only looks at its
>> own buffers to determine when to drop packets, and those only come into
>> play once the kernel's TCP buffers are filled.
>>
>>> so I had a couple thoughts towards using multiple rx queues in the
>>> vtun interface, and/or trying to read more than one packet at a
time
>>> (via recvmmsg) and do some level of fair queueing and queue
management
>>> (codel) inside tinc itself. I think that's
>>> pretty doable without modifying the protocol any, but I'm not
sure of
>>> it's value until I saturate some cpu more.
>>
>>
>> I'd welcome any work in this area :)
>>
>>> (and if you thought recvmsg was complex, look at recvmmsg)
>>
>>
>> It seems someone is already working on that, see
>> https://github.com/jasdeep-hundal/tinc.
>>
>>> D)
>>>
>>> the bottleneck link above is actually not tinc but the gateway, and
as
>>> the gateway reverts to codel behavior on a single encapsulated flow
>>> encapsulating all the other flows, we end up with about 40ms of
>>> induced delay on this test. While I have a better codel (gets below
>>> 20ms latency, not deployed), *fq*_codel by identifying individual
>>> flows gets the induced delay on those flows down below 5ms.
>>
>>
>> But that should improve with ECN if fq_codel is configured to use that,
>> right?
>>
>>> At one level, tinc being so nicely meshy means that the
"fq" part of
>>> fq_codel on the gateway will have more chance to work against the
>>> multiple vpn flows it generates for all the potential vpn
endpoints...
>>>
>>> but at another... lookie here! ipv6! 2^64 addresses or more to use!
>>> and port space to burn! What if I could make tinc open up 1024
ports
>>> per connection, and have it fq all it's flows over those? What
could
>>> go wrong?
>>
>>
>> Right, hash the header of the original packets, and then select a port
>> or address based on the hash? What about putting that hash in the flow
>> label of outer packets? Any routers that would actually treat those as
>> separate flows?
>
>
> -- Sent from my Android device with K-@ Mail. Please excuse my brevity.
>
> _______________________________________________
> Cerowrt-devel mailing list
> Cerowrt-devel at lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>


-- 
Dave T?ht

thttp://www.bufferbloat.net/projects/bloat/wiki/Upcoming_Talks

On Wed, Dec 3, 2014 at 4:02 AM, Guus Sliepen <guus at tinc-vpn.org>
wrote:
> On Wed, Dec 03, 2014 at 12:07:59AM -0800, Dave Taht wrote:
>
> [...]
>> https://github.com/dtaht/tinc
>>
>> I successfully converted tinc to use sendmsg and recvmsg, acquire (at
>> least on linux) the TTL/Hoplimit and IP_TOS/IPv6_TCLASS packet fields,
>
> Windows does not have sendmsg()/recvmsg(), but the BSDs support it.
>
>> as well as SO_TIMESTAMPNS, and use a higher resolution internal clock.
>> Got passing through the dscp values to work also, but:
>>
>> A) encapsulation of ecn capable marked packets, and availability in
>> the outer header, without correct decapsulationm doesn't work well.
>>
>> The outer packet gets marked, but by default the marking doesn't
make
>> it back into the inner packet when decoded.
>
> Is the kernel stripping the ECN bits provided by userspace? In the code
> in your git branch you strip the ECN bits out yourself.
Linux, at least, gives access to all 8 bits of the tos field on udp.

Windows does not, unless you have admin privs. Don't know
about other OSes.

The comment there:

 tos = origpkt->tos & ~0x3 ; // chicken out on passing ecn for now

was due to seeing this happen otherwise (talking to a tinc not yet
modified to decapsulate ecn markings correctly)

http://snapon.lab.bufferbloat.net/~d/tinc/ecn.png

and

was awaiting some thought on a truth table derived from the
relevant rfc (which I think is slightly wrong, btw), and further
thought on determining if ecn could be used on that path.

certainly I could deploy a tinc modified to assume ecn was
in use, (and may, shortly!) with the right truth table.

There was a comment higher up in the file also -
I would like to decrement hopcount/ttl
on the encapsulated packet by the
actual number of hops in the overlay path, not by one,
as is the default here, and in many other vpns.

This would decrease the damage caused by
routing loops.
>> So communicating somehow that a path can take ecn (and/or diffserv
>> markings) is needed between tinc daemons. I thought of perhaps
>> crafting a special icmp message marked with CE but am open to ideas
>> that would be backward compatible.
>
> PMTU probes are used to discover whether UDP works and how big the path
> MTU is, maybe it could be used to discover whether ECN works as well?
Yes.
> Set one of the ECN bits on some of the PMTU probes, and if you receive a
> probe with that ECN bit set, also set it on the probe reply.
This is an encapsulated packet vs an overt ping? Seems saner to test
over the encapsulation in this case.
>If you
> succesfully receive a reply with ECN bits set, then you know ECN works.
Well it should test for both CE and ECT(0) being set on separate
packets.
> Since the remote side just echoes the contents of the probe, you could
> also put a copy of the ECN bits in the probe payload, and then you can
> detect if the ECN bits got zeroed. You can also define an OPTION_ECN in
> src/connection.h, so nodes can announce their support for ECN, but that
> should not be necessary I think.
Not sure.
>
>> B) I have long theorized that a lot of userspace vpns bottleneck on
>> the read and encapsulate step, and being strict FIFOs,
>> gradually accumulate delay until finally they run out of read socket
>> buffer space and start dropping packets.
>
> Well, encryption and decryption takes a lot of CPU time, but context
> switches are also bad.
>
> Tinc is treating UDP in a strictly FIFO way, but actually it does use a
> RED algorithm when tunneling over TCP. That said, it only looks at its
One of these days I'll get around to writing a userspace codel lib
in pure C. Or someone else will.

The C++ versions in ns2, ns3, and mahimahi are hard to read. My currently
pretty elegant codel2.h might be a starting point, if only
I could solve count increasing without bound sanely.
> own buffers to determine when to drop packets, and those only come into
> play once the kernel's TCP buffers are filled.
TCP small queues (TSQ) and BQL should be a big boon to vpn and tor users.
>> so I had a couple thoughts towards using multiple rx queues in the
>> vtun interface, and/or trying to read more than one packet at a time
>> (via recvmmsg) and do some level of fair queueing and queue management
>> (codel) inside tinc itself. I think that's
>> pretty doable without modifying the protocol any, but I'm not sure
of
>> it's value until I saturate some cpu more.
>
> I'd welcome any work in this area :)
Well, I have to get packet timestamping to give sane results, and then
come up with saturating workloads for my hardware. This is easy for
cerowrt - I doubt the mips 640mhz processor can encrypt and push
even as much as 2mbit/sec....

but my "vision" such as it was, was to toss a beaglebone box
in as a vpn gateway instead, (on comcast's dynamically assigned
ipv6 networks) and maybe fiddle with the

http://cryptotronix.com/products/cryptocape/

which has a new kernel driver....

(it was a weekend, it was raining, I needed to get to my lab in
 los gatos from gf's in SF and
 ssh tunneling and portforwarding was getting bothersome...

 so I hacked on tinc. :) )
>> (and if you thought recvmsg was complex, look at recvmmsg)
>
> It seems someone is already working on that, see
> https://github.com/jasdeep-hundal/tinc.
Seemed to be mostly windows related hacking.

I am not ready to consider all the infrastructure required to
accumulate and manage packets inside of tinc, nor (after
fighting with recvmsg/sendmsg for 2 days) ready to tackle
recvmmsg... or threads and ringbuffers and all the headache
that entails.
>> D)
>>
>> the bottleneck link above is actually not tinc but the gateway, and as
>> the gateway reverts to codel behavior on a single encapsulated flow
>> encapsulating all the other flows, we end up with about 40ms of
>> induced delay on this test. While I have a better codel (gets below
>> 20ms latency, not deployed), *fq*_codel by identifying individual
>> flows gets the induced delay on those flows down below 5ms.
>
> But that should improve with ECN if fq_codel is configured to use that,
> right?
Meh. Ecn is very useful on very short or very long paths where
packet loss as an indicator of congestion is hurtful. In the general
case it adds a tiny bit to overall latency for other flows as congestion is not
cleared for an RTT, instead of at the bottleneck, with a loss.

This is still overly optimistic, IMHO:

https://tools.ietf.org/html/draft-ietf-aqm-ecn-benefits-00

current linux pie, red and codel do not enable ecn by default,
currently. Arguably pie could (because it has overload protection),
but codel, no.

Have a version of codel and fq_codel (and cake) that do
ecn overload protection, and enable ecn by default, am testing...

fq_codel enables ECN by default, (overload does very little
harm)

but openwrt (not cerowrt)
turns it off on their qos-scripts. It's half on by default in sqm-scripts,
and works pretty well if you have enough bandwidth - I
routinely run a few low latency networks with near zero packet loss,
and near-perfect utilization... which impresses me, at least...

ECN makes me nervous in general when enabled outside the
datacenter, but as something like 60% of the alexa top 1million
will enable ecn if asked nowadays, I hope that that worry extends
to enough more people for me to worry less.

http://ecn.ethz.ch/

I am concerned that enabling ECN generally breaks Tor over tcp
even worse at the moment.... (I hadn't thought about it til
my last message)

Certainly I think ECN is a great idea for vpns so long as it is
implemented correctly, although my understanding of CTR
mode over udp is that loss hurts not, and neither does
reordering?

In tinc: what if I get a packet with a seqno 5 after receiving packets
with seq 1-4,6-255. does that get dropped due to the replay protection,
or (if it passes muster) get decrypted and forwarded even after that much
reordering?

(I am all in favor of not worrying about reordering much. wifi aps
 tend to do it a lot, so do route flaps, and linux tcp, at least, is
 now VERY resistant to reordering problems, handling megabytes
 of out of order delivery problems with aplomb.

 windows on the other hand, sucks in this department,
still)
>
>> At one level, tinc being so nicely meshy means that the "fq"
part of
>> fq_codel on the gateway will have more chance to work against the
>> multiple vpn flows it generates for all the potential vpn endpoints...
>>
>> but at another... lookie here! ipv6! 2^64 addresses or more to use!
>> and port space to burn! What if I could make tinc open up 1024 ports
>> per connection, and have it fq all it's flows over those? What
could
>> go wrong?
>
> Right, hash the header of the original packets, and then select a port
> or address based on the hash?
Yes. I am leaning towards ipv6 address rather than port, you rapidly
run out of ports in ipv4, and making this an ipv6 specific feature
seems safer to test.

I look forward to messing up the expectations of many a stateful
ipv6 firewall....
>What about putting that hash in the flow
> label of outer packets? Any routers that would actually treat those as
> separate flows?
The flow label was a pretty good idea shot down by too many people
arguing over the bits. I don't think there is a lot of useful information
stored there in any coherent way, (it's too bad that the vxlan stuff
added a prepended header, instead of just using the flowlabel)

so it is best to just hash the main
headers and whatever inner headers you can obtain, as per

http://lxr.free-electrons.com/source/net/core/flow_dissector.c#L54

and

https://github.com/torvalds/linux/blob/master/net/sched/sch_fq_codel.c#L70

I have quibble with the jhash3 here, as the present treatment
of ipv6 is the very efficient but not very hashy

addr[0] ^ addr[2] ^ addr[3] ^ addr[4] (somewhere in the code),
instead of feeding all the bits to the hash function(s).

>
> --
> Met vriendelijke groet / with kind regards,
>      Guus Sliepen <guus at tinc-vpn.org>
>
> _______________________________________________
> tinc-devel mailing list
> tinc-devel at tinc-vpn.org
> http://www.tinc-vpn.org/cgi-bin/mailman/listinfo/tinc-devel


-- 
Dave T?ht

thttp://www.bufferbloat.net/projects/bloat/wiki/Upcoming_Talks