On 2020-02-10 07:36, teor wrote:

Hi,

Hi teor,

I'm including some comments below.

Here is an initial draft of Proposal 313: Relay IPv6 Statistics.

This proposal includes:

• logging the number of IPv6 relays in the consensus, and
• relays publishing IPv6 connection and consumed bandwidth statistics.

This is the third of 3 proposals:

• Proposal 311: Relay IPv6 Reachability
• Proposal 312: Automatic Relay IPv6 Addresses
• Proposal 313: Relay IPv6 Statistics

I revised proposals 311 and 312 last week, and merged them to torspec as drafts.

There are still some TODO items in the proposal, about:

• safely collecting these new statistics on bridges, and
• getting accurate IPv6 connection statistics.

If you know about tor's statistics, please give us some feedback!

The full text is included below, and it is also available as a GitHub pull request: https://github.com/torproject/torspec/pull/108

The related tickets are #33159 (proposal) and #33051 and #33052 (implementation): https://trac.torproject.org/projects/tor/ticket/33159 https://trac.torproject.org/projects/tor/ticket/33051 https://trac.torproject.org/projects/tor/ticket/33052

Please feel free to reply on this list, or via GitHub pull request comments.

Filename: 313-relay-ipv6-stats.txt Title: Relay IPv6 Statistics Author: teor Created: 10-February-2020 Status: Draft Ticket: #33159

0. Abstract

   We propose that Tor relays (and bridges) should log the number of relays in the consensus that support IPv6 extends, and IPv6 client connections.

   We also propose that Tor relays (and bridges) should collect statistics on IPv6 connections and consumed bandwidth. Like tor's existing connection and consumed bandwidth statistics, these new IPv6 statistics will be published in each relay's extra-info descriptor.

1. Introduction

   Tor relays (and bridges) can accept IPv6 client connections via their ORPort. But current versions of tor need to have an explicitly configured IPv6 address (see [Proposal 312: Relay Auto IPv6 Address]), and they don't perform IPv6 reachability self-checks (see [Proposal 311: Relay IPv6 Reachability]).

   As we implement these new IPv6 features in tor, we want to monitor their impact on the IPv6 connections and bandwidth in the tor network.

   Tor developers also need to know how many relays support these new IPv6 features, so they can test tor's IPv6 reachability checks. (In particular, see section 4.3.1 in [Proposal 311: Relay IPv6 Reachability]: Refusing to Publish the Descriptor.)

2. Scope

   This proposal modifies Tor's behaviour as follows:

   Relays, bridges, and directory authorities log the number of relays that support IPv6 clients, and IPv6 relay reachability checks. They also log the corresponding consensus weight fractions.

   As an optional change, tor clients may also log this information.

   Relays, bridges, and directory authorities collect statistics on:

   • IPv6 connections, and
   • IPv6 consumed bandwidth.

   The design of these statistics will be based on tor's existing connection and consumed bandwidth statistics.

   Tor's existing consumed bandwidth statistics truncate their totals to the nearest kilobyte. The existing connection statistics do not perform any binning.

   We do not proposed to add any extra noise or binning to these statistics. Instead, we expect to leave these changes until we have a consistent privacy-preserving statistics framwework for tor. As an example of this kind of framework, see [Proposal 288: Privacy-Preserving Stats with Privcount (Shamir version)].

   We avoid:

   • splitting connection statistics into clients and relays, and
   • collecting circuit statistics.

   These statistics are more sensitive, so we want to implement privacy-preserving statistics, before we consider adding them.

   Throughout this proposal, "relays" includes directory authorities, except where they are specifically excluded. "relays" does not include bridges, except where they are specifically included. (The first mention of "relays" in each section should specifically exclude or include these other roles.)

   Tor clients do not collect any statistics for public reporting. Therefore, clients are out of scope in this proposal. (Except for some optional changes to client logs, where they log the number of IPv6 relays in the consensus).

   When this proposal describes Tor's current behaviour, it covers all supported Tor versions (0.3.5.7 to 0.4.2.5), as of January 2020, except where another version is specifically mentioned.

3. Logging IPv6 Relays in the Consensus

   We propose that relays (and bridges) log:

   • the number of relays, and
   • the consensus weight fraction of relays,

   in the consensus that:

   • have an IPv6 ORPort,
   • support IPv6 reachability checks, and
   • support IPv6 clients.

   In order to test these changes, and provide easy access to these statistics, we propose implementing a script that:

   • downloads a consensus, and
   • calculates and reports these statistics.

   As well as the statistics listed above, this script should also report the following relay statistic:

   • support IPv6 reachability checks and IPv6 clients.

   The following consensus weight fractions should divide by the total consensus weight:

   • have an IPv6 ORPort (all relays have an IPv4 ORPort), and
   • support IPv6 reachability checks (all relays support IPv4 reachability).

   The following consensus weight fractions should divide by the "usable Guard" consensus weight:

   • support IPv6 clients, and
   • support IPv6 reachability checks and IPv6 clients.

   "Usable Guards" have the Guard flag, but do not have the Exit flag. If the Guard also has the BadExit flag, the Exit flag should be ignored.

This definition is different from the one we're using in Onionoo for computing the "guard probability". There we include a relay with the Guard flag, regardless of whether it has the Exit and/or BadExit flag. Not sure if this matters and which definition is more useful, I just wanted to point out that they're different.

We propose that these logs happen whenever tor: * receives a consensus from a directory server, or * loads a live, valid, cached consensus from disk.

As an optional change, tor clients may also log this information. Some of this information is not directly relevant to clients, but these logs may help developers (and users).

4. Collecting IPv6 Consumed Bandwidth Statistics

   We propose that relays (and bridges) collect IPv6 consumed bandwidth statistics.

   To minimise development and testing effort, we propose re-using the existing "bw_array" code in rephist.c.

   In particular, tor currently counts these bandwidth statistics:

   • read,
   • write,
   • dir_read, and
   • dir_write.

   We propose adding the following bandwidth statistics:

   • ipv6_read, and
   • ipv6_write.

   (The IPv4 statistics can be calculated by subtracting the IPv6 statistics from the existing total consumed bandwidth statistics.)

   We propose adding a new BandwidthStatistics torrc option and consensus parameter, which activates reporting of all these statistics. Currently, the existing statistics are controlled by ExtraInfoStatistics, but we propose using the new BandwidthStatistics option for them as well.

   The default value of this option should be "auto", which checks the consensus parameter. If there is no consensus parameter, the default should be 1. (The existing bandwidth statistics are reported by default.)

   TODO: Should we collect IPv6 bandwidth statistics on bridges? On bridges, should bandwidth statistics be on or off by default?

     If we do want to collect bridge statistics, and we think it's safe,
     modify proposals 311 and 312 to allow bridge statistics.
   

Right now, bandwidth statistics are on by default on bridges. I'd think that turning them off by default as part of this proposal would be surprising. It would be better, in terms of less surprising, to have a replacement first before making that change.

Regardless of defaults, I'd say that collecting IPv6 bandwidth statistics over a period of 24 hours is about as safe as collecting IPv4+IPv6 bandwidth statistics over a period of 24 hours.

5. Collecting IPv6 Connection Statistics

   We propose that relays (and bridges) collect IPv6 connection statistics.

   To minimise development and testing effort, we propose re-using the existing "bidi" code in rephist.c. (This code may require some refactoring, because the "bidi" totals are globals, rather than a struct.)

   In particular, tor currently counts these connection statistics:

   • below threshold,
   • mostly read,
   • mostly written, and
   • both read and written.

   We propose adding IPv6 variants of all these statistics. (The IPv4 statistics can be calculated by subtracting the IPv6 statistics from the existing total connection statistics.)

   We propose using the existing ConnDirectionStatistics torrc option, and adding a consensus parameter with the same name. This option will control the new and existing connection statistics.

   The default value of this option should be "auto", which checks the consensus parameter. If there is no consensus parameter, the default should be 0. (The existing connection direction statistics are reported by default.)

   TODO: Do enough relays report ConnDirectionStatistics, for accurate IPv6 connection statistics?

   • at least 25% of relays have IPv6
   • at the end of the project, we expect at least 33% of relays to have deployed tor 0.4.4-stable

   If not, we should turn on ConnDirectionStatistics by default. (Or set the consensus parameter for a few days, to collect these statistics.)

It looks like these statistics are turned off by default, yet they are reported in 79,709 out of 80,468 recent extra-info descriptors I just looked at. Something's wrong in the current code, though I didn't spot it at a quick glance. If it's accidentally turned on by default, I think that changing it to a consensus parameter and turning that on for a few days only would be a good solution.

That's my last comment. Overall looks like a great proposal!

All the best, Karsten

6. Directory Protocol Specification Changes

   We propose adding IPv6 variants of the consumed bandwidth and connection direction statistics to the tor directory protocol.

   We propose the following additions to the [Tor Directory Protocol] specification, in section 2.1.2. Each addition should be inserted below the existing consumed bandwidth and connection direction specifications.

   "ipv6-read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL [At most once] "ipv6-write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL [At most once]

    Declare how much bandwidth the OR has used recently, on IPv6
    connections. See "read-history" and "write-history" for more details.
    (The migration notes do not apply to IPv6.)
   
   

   "ipv6-conn-bi-direct" YYYY-MM-DD HH:MM:SS (NSEC s) BELOW,READ,WRITE,BOTH NL [At most once]

    Number of IPv6 connections, that are used uni-directionally or
    bi-directionally. See "conn-bi-direct" for more details.
   
   

   We also propose the following replacement, in the same section:

   "dirreq-read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL [At most once] "dirreq-write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL [At most once]

    Declare how much bandwidth the OR has spent on answering directory
    requests. See "read-history" and "write-history" for more details.
    (The migration notes do not apply to dirreq.)
   
   

   This replacement is optional, but it may avoid the 3 *read-history definitions getting out of sync.

7. Optional Changes

   We propose some optional changes to help relay operators, tor developers, and tor's network health. We also expect that these changes will drive IPv6 relay adoption.

   Some of these changes may be more appropriate as future work, or along with other proposed features.

7.1. Log IPv6 Statistics in Tor's Heartbeat Logs

We propose this optional change, so relay operators can see their own IPv6 statistics:

We propose that tor logs its IPv6 consumed bandwidth and connection statistics in its regular "heartbeat" logs.

These heartbeat statistics should be collected over the lifetime of the tor process, rather than using the state file, like the statistics in sections 4 and 5.

Tor's existing heartbeat logs already show its consumed bandwidth and connections (in the link protocol counts).

We may also want to show IPv6 consumed bandwidth and connections as a propotion of the total consumed bandwidth and connections.

These statistics only show a relay's local bandwidth usage, so they can't be used for reporting.

7.2. Show IPv6 Statistics on Consensus Health

The [Consensus Health] website displays a wide rage of tor statistics, based on the most recent consensus.

We propose this optional change, to: * help relay operators diagnose issues with IPv6 on their relays, and * to drive IPv6 adoption on tor relays.

Consensus Health adds an IPv6 section, with the following relay statistics: * have an IPv6 ORPort, * support IPv6 reachability checks, * support IPv6 clients, and * support IPv6 reachability checks and IPv6 clients.

The definitions of these statistics are in section 3.

These changes can be tested using the script proposed in section 3.

7.3. Add an IPv6 Reachability Pseudo-Flag on Relay Search

The [Relay Search] website displays tor relay information, based on the current consensus and relay descriptors.

We propose this optional change, to: * help relay operators diagnose issues with IPv6 on their relays, and * drive IPv6 adoption on tor relays.

Relay Search adds a pseudo-flag for relay IPv6 reachability support.

This pseudo-flag should be given to relays that have: * a reachable IPv6 ORPort (in the consensus), and * support tor subprotocol version "Relay=3" (or later). See [Proposal 311: Relay IPv6 Reachability] for details.

TODO: Is this a useful change? Are there better ways of driving IPv6 adoption?

7.4. Add IPv6 Connections and Consumed Bandwidth Graphs to Tor Metrics

The [Tor Metrics: Traffic] website displays connection and bandwidth information for the tor network, based on relay extra-info descriptors.

We propose these optional changes, to: * help tor developers improve IPv6 support on the tor network, * help diagnose issues with IPv6 on the tor network, and * drive IPv6 adoption on tor relays.

Tor Metrics adds the following information to the graphs on the Traffic page:

Consumed Bandwidth by IP version * added to the existing [Tor Metrics: Advertised bandwidth by IP version] page * as a stacked graph, like [Tor Metrics: Advertised and consumed bandwidth by relay flags]

Fraction of connections used uni-/bidirectionally by IP version * added to the existing [Tor Metrics: Fraction of connections used uni-/bidirectionally] page * as a stacked graph, like [Tor Metrics: Advertised and consumed bandwidth by relay flags]

8. Test Plan

   We provide a quick summary of our testing plans.

8.1. Testing IPv6 Relay Consensus Count Logging

We propose to test these changes using chutney networks. However, chutney creates a limited number of relays, so we also need to test these changes on the public tor network.

Therefore, we propose to test these changes on the public network with a small number of relays and bridges.

We can use the script and the tor logs to cross-check these calculations. The Tor Metrics team may also independently check these calculations.

Once these changes are merged, they will be monitored by tor developers, as more volunteer relay operators deploy the relevant tor versions. (And as the number of IPv6 relays in the consensus increases.)

8.2. Testing IPv6 Extra-Info Statistics

We propose to test the connection and consumed bandwidth statistics using chutney networks. However, chutney runs for a short amount of time, and creates a limited amount of traffic, so we also need to test these changes on the public tor network.

In particular, we have struggled to test statistics using chutney, because tor's hard-coded statistics period is 24 hours. (And most chutney networks run for under 1 minute.)

Therefore, we propose to test these changes on the public network with a small number of relays and bridges.

During 2020, the Tor Metrics team will analyse these statistics on the public tor network, and provide IPv6 progress reports. We expect that we may discover some bugs during the first analysis.

Once these changes are merged, they will be monitored by tor developers, as more volunteer relay operators deploy the relevant tor versions. (And as the number of IPv6 relays in the consensus increases.)

References:

[Tor Directory Protocol]: (version 3) https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt

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On Mon, Feb 10, 2020 at 1:37 AM teor teor@riseup.net wrote:

Hi, Teor! This proposal looks good and thorough to me. I have only a couple of questions on section 3:

3. Logging IPv6 Relays in the Consensus

   We propose that relays (and bridges) log:

   • the number of relays, and
   • the consensus weight fraction of relays,

   in the consensus that:

   • have an IPv6 ORPort,
   • support IPv6 reachability checks, and
   • support IPv6 clients.

I don't understand the motivation behind doing this in the Tor code, since it's not something that relay operators need to know about or take action on. To me, it seems more like something do do as part of metrics than in Tor per se.

[...]

"Usable Guards" have the Guard flag, but do not have the Exit flag. If the Guard also has the BadExit flag, the Exit flag should be ignored.

It seems to me that this rule should depend on the Wgd bandwidth-weights value ("Weight for Guard+Exit-flagged nodes in the guard Position"), right? (Right now that is zero, and I don't expect it to change.)

See also Karsten's response here for more information.