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Last updated: [[User:Mstone|Michael Stone]] 04:15, 15 January 2010 (UTC) | '''[[Network2/Paper|paper version]]'''
= Introduction =


Sugar's desired realtime collaboration experience can only be provided atop a robust and efficient network stack designed to accommodate automated diagnosis and standardized workarounds -- anything less only wastes students' and teachers' time and patience, contrary to our [[OLPC Human Interface Guidelines/Design Fundamentals/Key Design Principles|human interface guidelines]].
Last updated: [[User:Mstone|Michael Stone]] 05:11, 18 July 2009 (UTC)


This '''unfinished''' essay summarizes an attempt to work out a simple way to realize this sort of network experience, with existing software and hardware, while also demonstrating the sort of thinking which might help other parts of the system achieve the same standard of quality.
This document proposes a design for networking based on previously realized [[Network Principles]]. It then explores and elaborates the design with analysis, example configuration, and experimental results after which it concludes by crediting those who have contributed to the design and by explaining future work inspired by current results.


'''Quick links''': '''[[Network2/Paper|the Paper]]''' : (finished/''unfinished'' sections)
: ''(If you've contributed and don't see your name, don't fret -- just add yourself with a word or two explaining your contribution!)''


* Prior work: [[networking]], [[collaboration]], [[network principles]]
Some important quality criteria to consider while reading it include:
* Background: [[Network2/Purpose|purpose]], [[Network2/Scenarios|scenarios]], [[Network2/Architecture|architecture]]
* Designs: [[Network2/Design|naming and internetworking]], ''[[Network2/Security|security ideas]]'', [[Network2/Diagnosis|diagnosis techniques]]
* Analyses: ''[[Network2/Dynamics|cost model]]'', ''[[Network2/Self-test|self-test algorithm]]''
* Experiments: [[Network2/Experiments/Dnshash|dnshash]], [[Network2/Experiments/Openvpn|openvpn]], ''[[Network2/Experiments/HE|6to4: HE]]'', ''[[Network2/Experiments/Sixxs|6to4: Sixxs]]'', ''[[Network2/Experiments/Simulation|simulation]]'', ''[[Network2/Experiments/openwrt|openwrt]]'', ''[[Network2/Experiments/tinydns|olpcdyndns1]]''


'''Personal goals...'''
; primum, non nocere
: People usually think that sufferance of free software is voluntary but this is not so for our users.
: ''First, do no harm.''


# "I want to use familiar tools in my activities, -- like Twisted, curl, ssh, rsync, and email -- both under a tree, in a walled garden, and out on the public Internet, without modification or wrappers."
; no lock-in
# "I want a design that has 20% fewer ways to fail, and that offers manual overrides for the failure modes that remain."
: Does the success of the design depend on any ideas which lack pre-existing interoperating implementations?
# "I want to chop 2-3 levels from the current collaboration stack's 6-level 'fast-path'."
: ''What existing software is it presently incompatible with? What does that cost to change?''
# "I want to collaborate with people who only have web browsers -- they outnumber people with Jabber clients by millions."


'''Finally, to help out''', please improve my writing, experiment with my ideas, and share this work with your friends!
; no ponies
: How well does the design conform to the physical and social realities which define its niche?
: ''For example: bandwidth, latency, error, ignorance, interdiction, authority, autonomy...''


==Subpages==
When judging, please also note that the design is '''not yet complete''' in several important respects:
{{Special:PrefixIndex/{{PAGENAMEE}}/}}
* it has only a stub of a bandwidth model,
* its self-test algorithm is not yet written, (though good diagnostic primitives are systematically identified)
* it lacks truly clear implementation guidance and comprehensive sample code, and
* there are unresolved questions about
** how routing and timeouts should be configured so that peers search their target address space in a useful fashion
** how [[communications security]] might best be provided.


= Design =


[[Category:Network2]]
== Protocols and Axioms ==
[[Category:Subsystems]]

We imagine our network as organized into three layers:

; a data link layer
: usually implemented via 802.3 wired Ethernet, 802.11b/g wifi in either ad-hoc or infrastructure mode, or a NATed IPv4 subnet
; a transient logical layer
: based on [http://tools.ietf.org/html/rfc2460 IPv6] ([http://tldp.org/HOWTO/html_single/Linux+IPv6-HOWTO/ tutorial documentation])
; a stable logical layer
: which binds human-meaningful [http://tools.ietf.org/html/rfc1034 DNS] names to transient logical addresses.

A couple of key facts and expectations inform the rest of this design, like:

* hosts will have multiple interfaces,
* interfaces will have multiple addresses,
* DNS queries (used via <tt>getaddrinfo()</tt>) will return multiple results
* these results will be sorted in a [http://tools.ietf.org/html/rfc3484 sane order], and
* hosts will choose routes for packets based on how specifically the routes match the destination and on any QoS information available to the routing node.

== Peer IPv6 Configuration ==

Your job is to be an IPv6 node. Consequently, when you bring up your interfaces,

# You might [http://tools.ietf.org/html/rfc2461 discover] an IPv6 router [http://tools.ietf.org/html/rfc2463 advertising] on one of your links.
#* (See <tt>sysctl net.ipv6.conf.all.accept_ra</tt> and related variables.)
# You might try out [https://fedorahosted.org/dhcpv6/ dhcp6c].
# You might have some kind of IPv4 connectivity. If so, [http://www.sixxs.net/faq/connectivity/?faq=comparison connect] to the Internet or to other internetworks of your choice.
#* ([http://www.remlab.net/miredo/ miredo] and [http://openvpn.net/ openvpn] seem particularly easy to configure and hence to experiment with...)
# Use [[dnshash]] to add guessable link-local addresses to all your links.

== Server IPv6 Configuration ==

Your job is to be an IPv6 router and a [http://tools.ietf.org/html/rfc1035 DNS server]. One of several situations might obtain:

# You might discover an IPv6 router advertising one or more IPv6 prefixes on your outbound link(s).
# You might have some kind of IPv4 connectivity. If so, [http://www.sixxs.net/faq/connectivity/?faq=comparison connect] to the Internet or to other internetworks of your choice.
# You might be under a tree. If so, generate a [http://tools.ietf.org/html/rfc4193 Unique Local Address] prefix.
# (Use [[dnshash]] to add guessable link-local addresses to all your links?)

When done, use [http://www.litech.org/radvd/ radvd] or [https://fedorahosted.org/dhcpv6/ dhcp6d] to share addresses.

== Server DNS Configuration ==

One of the server's most important jobs is to get itself on appropriate internetworks so that it can dynamically map stable (DNS) names to unstable names (IPv6 addresses) for itself and its peers.

Unfortunately, the most reliable and secure means of updating these mappings is likely to be bespoke -- [http://tools.ietf.org/html/rfc2136 RFC 2136] is not widely implemented and specifies no concrete security protocol while DNSSEC seems immature at present.

Consequently, I propose the following strawman update protocol -- exchange an RFC-2136 UPDATE packet and response over your favorite authenticated RPC protocol with the nameserver.

(My favorite protocol for this sort of thing is currently "json-over-SSH-to-python-and-make", but variations (ucspi-ssl, 9p, etc.) make me smile.)

''(Other possibilities: maybe DNSSEC isn't so hard? Maybe DNSCurve will be usable? See [http://ipcheck.sourceforge.net/ ipcheck] and [http://ddclient.sourceforge.net ddclient] for contemporary work...)''

== Peer DNS Configuration ==

Peers which have been registered with one or more servers need to update those servers when their addresses change using the protocol described above.


== Security Ideas ==

# Spoofing, Integrity, Confidentiality. See [[communications security]] and [http://passpet.org/ petnames] for some background. A very rough road along which something reasonable ''might'' lie:
#* Use [http://dev.laptop.org/git/projects/barcode physical introduction] to CNAME <tt>cscott.michael.laptop.org</tt> to <tt>''&lt;key&gt;''.cscott.laptop.org</tt>.
#* Then, my [http://dnscurve.org dnscurve]-compatible DNS resolver will refuse to give me addresses unless the nameserver I contact for cscott proves knowledge of cscott's private key.
#* Then I have a nice basis with which to configure IPsec security associations.
# System Integrity
# DoS

= Analysis =

== Bandwidth Usage ==

Several important numbers that we need to predict and to measure:

tx == transmit, rx == receive, btx == broadcast
btx/tx/rx - ICMPv6+IPv6+phys - router discovery (RD)
btx/rx - ICMPv6+IPv6+phys - duplicate address detection (DAD)
tx/rx - ICMPv6+IPv6+phys - NS neighbor discovery (ND)
tx/rx - UDP+IPv6+phys - DNS query
tx/rx - JSON+SSH+TCP+IPv6+phys - DNS update
where "phys" describes the equations' dependence on the "physical" layer's
frame overhead and MTU
notable "phys" layers:
Ethernet -- ad-hoc wifi, infra wifi, 802.11s mesh, switch, hub
TLS+UDP+IPv4 -- openvpn
L2TP+IPsec+IPv4 -- raccoon, isakmpd, openswan, etc.
UDP+IPv4 -- teredo

== Debugging Techniques ==

Start recording a typescript so that we can see what you did.

TESTDIR=`pwd`/testing
mkdir -p $TESTDIR && cd TESTDIR
script
ulimit -c unlimited

Check that you've got the right DNS name for the person you want to talk to.

NAME=the.right.person
echo $NAME > peer

Dump your addresses, routes, and perhaps your open connections.

hostname --fqdn | tee host
ip addr show | tee addrs
ip route show | tee ipv4_routes
ip -6 route show | tee ipv6_routes
netstat -anp | tee conns

If you have wireless devices,

iwconfig | tee iwconfig
iwlist scan | tee iwlist_scan

Fire up tcpdump:

tcpdump -w packets -s0 &

Resolve that name to addresses. Check that the addresses seem sane.

dnshash lookup $NAME | tee peer_addrs_dnshash
dig $NAME | tee peer_addrs_dig

See who's answering broadcasts:

ping6 -I $IFACE ff02::1

Route to the addresses:

ping6 -I $IFACE $ADDR | tee ping
traceroute6 $ADDR | tee traceroute
tracepath6 $ADDR | tee tracepath

Connect to the address:

nc6 $ADDR $PORT
# echo "SSH-2.0-Hi" | nc6 $ADDR 22
# printf "GET / HTTP/1.0\r\n\r\n" | nc6 $ADDR 80
# ssh $ADDR
# curl -I http://$ADDR/
# ...

Conduct a bandwidth test:

iperf -c -V $ADDR

Collect logs from your application and send them to developers:

kill -SIGINT %1
cd ..
tar c $TESTDIR | lzma -c > logs.tar.lzma

== Self-Test Algorithm ==

As we gain experience with the system, we'll write a decision-list here which inspects the output of the diagnostic procedures listed above and which identifies the proximate cause of networking failure based on those results.

== Advice for Coders ==

There are two critical changes that you'll need to make to your design in order to really make it sing.

First, you'll want to add some mechanism for your users to type in hostnames that they want you to connect to. This lets them do all sorts of cool stuff like:

* copy-and-paste links from websites or cerebro
* type in names from a physical display like a blackboard or a handout,

Second, you'll want to be prepared to re-resolve names in order to get fresh addresses each time your connectivity changes. For the time being, you should do this by calling libc's <tt>[http://linux.die.net/man/3/getaddrinfo getaddrinfo()]</tt> function.

Third, go check out [http://tools.ietf.org/html/rfc4960 SCTP] ([http://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocol wikipedia], [http://linux.die.net/man/7/sctp man page]). It's support for multi-homing, multi-streaming with and without ordering guarantees, and for updating the addresses you're using to talk to your peer on the fly seem particularly serendipitous.

== Advice for Deployers ==

Ask your ISPs to provide IPv6 prefixes or tunnel endpoints. After all -- if none of their customers ask, then what incentive will they ever have to upgrade?

Failing that, see if you (or a local university?) can afford a public IPv4 address -- even if it's dynamic. If so, you can be many sorts of tunnel endpoint.

Regardless, if you manage to get a globally reachable IPv6 address by any means, then you can provide a DNS server for your kids and it can direct them to one another and to any other services that you feel like pointing them at.


= Experiments =

== Link-local configuration ==

Try out [[dnshash]] on an isolated access point, ad-hoc network, switch, or hub.

Observations: very pleasant!

== VPN server configuration ==

In this experiment, we're going to configure openvpn and radvd on a machine (teach.laptop.org) with a public IPv4 address. Truthfully, this combination is probably overkill, but the task of constructing it seemed like it might to offer valuable experience, e.g. for someone who wants to bridge multiple kinds of tunnel endpoint or who wants to load-balance lots of peers between a couple of endpoints.

# Install our VPN and route advertisement software.
apt-get install openvpn radvd
# yum -y install openvpn radvd
# add nobody:nobody
groupadd nobody
useradd nobody
usermod -a -G nobody nobody
# Configure radvd
cat > /etc/radvd.conf <<EOF
interface tap0
{
AdvSendAdvert on;
MinRtrAdvInterval 30;
MaxRtrAdvInterval 100;
prefix 1234:db8:1:0::/64
{
AdvOnLink on;
};
};
EOF
# enable forwarding everywhere
sysctl -w net.ipv6.conf.all.forwarding=1
# flush the forwarding table
ip6tables -F FORWARD
# really, I /want/ a multi-user version of
# openvpn --dev tap --user nobody --group nobody --verb 6
# but I'm not sure how to get that. instead, I'll use some fake keys and no ciphers.
mkdir -P keys && cd keys
wget http://teach.laptop.org/~mstone/sample-keys.tar.bz2
tar xf sample-keys.tar.bz2 && cd sample-keys
# create a multi-user tunnel
openvpn --mode server --client-to-client --dev tap --user nobody --group nobody --verb 6 --opt-verify --tls-server --client-connect /bin/true --auth-user-pass-optional --duplicate-cn --auth-user-pass-verify /bin/true via-env --dh ./dh1024.pem --ca ./ca.crt --cert client.crt --key client.key --script-security 3 --auth none --cipher none &
# at any rate, bring up the interface so that we get link-local addresses
ip link set tap0 up
# turn on the route advertisement daemon
radvd -d 5 -m stderr &

== VPN client configuration ==

The purpose of this experiment was to test the VPN configuration described immediately above.

# install vpn client
apt-get install openvpn
# yum -y install openvpn
# add nobody:nobody
groupadd nobody
useradd nobody
usermod -a -G nobody nobody
# download fake keys.
mkdir -P keys && cd keys
wget http://teach.laptop.org/~mstone/sample-keys.tar.bz2
tar xf sample-keys.tar.bz2 && cd sample-keys
# connect to the vpn
openvpn --user nobody --group nobody --dev tap --remote teach.laptop.org --tls-client --ca ca.crt --cert ./client.crt --key client.key --auth none --cipher none &
# bring up the interface
ip link set tap0 up
# find other people
ping6 -I tap0 ff02::1
# if using dnshash, attach
dnshash attach <your>.<domain>.<name>
# ... test, as described above ...

Observations:

* TLS imposes a high latency cost, even with null algorithms.
* TAP devices work rather nicely, at least for tiny networks.
* Be careful of firewall rules!
* radvd is ''perhaps'' unnecessary with a single virtual ethernet -- dnshash "suffices" -- though it might be useful for routing between several load-balanced ethernets.
* The default IP sorting rules and route priorities mean that it may take a long time for a connecting app like ssh or nc6 to connect to the /correct/ dnshash address.

= Credits =

* {{credit|[[Profiles/mstone|Michael Stone]]|none|writing}}
* {{credit|[[Profiles/cscott|C. Scott Ananian]]|OLPC|architecture,teaching}}
* {{credit|[[Profiles/wad|John Watlington]]|OLPC|architecture}}
* {{credit|[[Profiles/robot101|Robert McQueen]]|Collabora|prior work,critique}}
* {{credit|[[Profiles/daf|Dafydd Harries]]|Collabora|prior work,critique}}
* {{credit|[[Profiles/ypod|Polychronis Ypodimatopolous]]|MIT|prior work,critique}}
* {{credit|[[Profiles/csetlow|Cortland Setlow]]|Tower Research Capital|testing}}
* {{credit|[[Profiles/aa|Andres Ambrois]]||design,testing}}
* {{credit|[[Profiles/bemasc|Benjamin Schwartz]]|Harvard|critique,publicity}}
* {{credit|[[Profiles/tabitha|Tabitha Roder]]||testing}}

= Future Work =

* Per-host networks and per-app IPs and names.
* Sample code.
* Designs for [[User:Mstone/Higher protocols|higher protocols]] like discovery, presence, and health.

Latest revision as of 04:15, 15 January 2010

Last updated: Michael Stone 04:15, 15 January 2010 (UTC) | paper version

Sugar's desired realtime collaboration experience can only be provided atop a robust and efficient network stack designed to accommodate automated diagnosis and standardized workarounds -- anything less only wastes students' and teachers' time and patience, contrary to our human interface guidelines.

This unfinished essay summarizes an attempt to work out a simple way to realize this sort of network experience, with existing software and hardware, while also demonstrating the sort of thinking which might help other parts of the system achieve the same standard of quality.

Quick links: the Paper : (finished/unfinished sections)

Personal goals...

  1. "I want to use familiar tools in my activities, -- like Twisted, curl, ssh, rsync, and email -- both under a tree, in a walled garden, and out on the public Internet, without modification or wrappers."
  2. "I want a design that has 20% fewer ways to fail, and that offers manual overrides for the failure modes that remain."
  3. "I want to chop 2-3 levels from the current collaboration stack's 6-level 'fast-path'."
  4. "I want to collaborate with people who only have web browsers -- they outnumber people with Jabber clients by millions."

Finally, to help out, please improve my writing, experiment with my ideas, and share this work with your friends!

Subpages

Retrieved from "http://wiki.laptop.org/mediawiki/index.php?title=Network2&oldid=230397"