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| author | Nick Mathewson <nickm@torproject.org> | 2019-01-28 11:31:47 +0100 |
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| committer | Nick Mathewson <nickm@torproject.org> | 2019-01-28 11:31:47 +0100 |
| commit | 5c19f4d1ca9a443ba14b07ad32e9bfe81080dbd8 (patch) | |
| tree | cba7ea6c389f899408010ca02e60fcce031db860 /proposals/299-ip-failure-count.txt | |
| parent | 6e9a14b030bc1a7b9d2919bda637d01ea34fc021 (diff) | |
| download | torspec-5c19f4d1ca9a443ba14b07ad32e9bfe81080dbd8.tar.gz torspec-5c19f4d1ca9a443ba14b07ad32e9bfe81080dbd8.zip | |
Add proposal 299 from Neel Chauhan
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| -rw-r--r-- | proposals/299-ip-failure-count.txt | 117 |
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diff --git a/proposals/299-ip-failure-count.txt b/proposals/299-ip-failure-count.txt new file mode 100644 index 0000000..6e09353 --- /dev/null +++ b/proposals/299-ip-failure-count.txt @@ -0,0 +1,117 @@ +Filename: 299-ip-failure-count.txt
+Title: Preferring IPv4 or IPv6 based on IP Version Failure Count
+Author: Neel Chauhan
+Created: 25-Jan-2019
+Status: Draft
+Ticket: https://trac.torproject.org/projects/tor/ticket/27491
+
+1. Introduction
+
+ As IPv4 address space becomes scarce, ISPs and organizations will deploy
+ IPv6 in their networks. Right now, Tor clients connect to guards using
+ IPv4 connectivity by default.
+
+ When networks first transition to IPv6, both IPv4 and IPv6 will be enabled
+ on most networks in a so-called "dual-stack" configuration. This is to not
+ break existing IPv4-only applications while enabling IPv6 connectivity.
+ However, IPv6 connectivity may be unreliable and clients should be able
+ to connect to the guard using the most reliable technology, whether IPv4
+ or IPv6.
+
+ In ticket #27490, we introduced the option ClientAutoIPv6ORPort which adds
+ preliminary "happy eyeballs" support. If set, this lets a client randomly
+ choose between IPv4 or IPv6. However, this random decision does not take
+ into account unreliable connectivity or network failures of an IP family.
+ A successful Tor implementation of the happy eyeballs algorithm requires
+ that unreliable connectivity on IPv4 and IPv6 are taken into consideration.
+
+ This proposal describes an algorithm to take into account network failures
+ in the random decision used for choosing an IP family and the data fields
+ used by the algorithm.
+
+2. Failure Counter Design
+
+ I propose that the failure counter uses the following fields:
+
+ * IPv4 failure count
+
+ * IPv4 failure count from no route (autofail)
+
+ * IPv6 failure count
+
+ * IPv6 failure count from no route (autofail)
+
+ These entries will exist as internal counters for the current session, and
+ as a list of the previous counts of these counters from previous sessions in
+ the state file.
+
+ These values will be stored as 32-bit unsigned integers for the current
+ session, and as comma seperated values in the statefile.
+
+ The list capacity will be the 4 most recent sessions for each field above
+ stored in the state file with the least recent first. This is for the
+ following reasons:
+
+ * We can forget about the oldest sessions without having to keep the
+ exact timestamp when a client failed. This prevents an attacker from
+ getting detailed failure information from the state file.
+
+ * Some clients (mobile phones, laptops) may switch between networks of
+ which may be more or less reliable than the previous in terms of IPv4
+ or IPv6. In this case, it makes less sense to remember old failures
+ caused on a different network from the current one.
+
+ When Tor is being closed, and there are less than four entries for each
+ field, we will append the current session at the end. If there are four
+ entries, we will remove the oldest entry and then add the current session's
+ values at Tor's shutdown.
+
+3. Failure Probability Calculation
+
+ The failure count of one IP version will increase the probability of the
+ other IP version. For instance, a failure of IPv4 will increase the IPv6
+ probability, and vice versa.
+
+ When the IP version is being chosen, I propose that these values will be
+ included in the guard selection code:
+
+ * IPv4 failure points
+
+ * IPv6 failure points
+
+ * Total failure points
+
+ These values will be stored as 32-bit unsigned integers.
+
+ A generic failure of an IP version will add one point to the failure point
+ count values of the particular IP version which failed.
+
+ A failure of an IP version from a "no route" error which happens when
+ connections automatically fail will be counted as two failure points
+ for the automatically failed version.
+
+ The failure points for both IPv4 and IPv6 is sum of the values in the state
+ file plus the current session's failure values. The total failure points is
+ a sum of the IPv4 and IPv6 failure points.
+
+ The probability of a particular IP version is the failure points of the
+ other version divided by the total number of failure points, multiplied
+ by 8 and stored as an integer. We will call this value the summarized
+ failure point value (SFPV). The reason for this summarization is to
+ emulate a probability in 1/8 intervals by the random number generator.
+
+ In the random number generator, we will choose a random number between 0
+ and 8. If the random number is less than the IPv6 SFPV, we will choose
+ IPv4. If it is equal or greater, we will choose IPv6.
+
+ If the probability is 0/8 with a SFPV value of 0, it will be rounded to
+ 1/8 with a SFPV of 1. Also, if the probability is 8/8 with a SFPV of 8,
+ it will be rounded to 7/8 with a SFPV of 7. The reason for this is to
+ accomodate mobile clients which could change networks at any time (e.g.
+ WiFi to cellular) which may be more or less reliable in terms of a
+ particular IP family when compared to the previous network of the client.
+
+4. Acknowledgements
+
+ Thank you teor for aiding me with the implementation of Happy Eyeballs in
+ Tor. This would not have been possible if it weren't for you.
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