Hi all, We would like to move IPv6 ORPorts from microdescriptors to the microdesc consensus. This makes it easier for IPv6 clients to bootstrap and choose reachable guards.
The proposal is inlined below, it is also available with the corresponding dir-spec updates in my torspec branch bug23826-23828 on GitHub: https://github.com/teor2345/torspec.git The tor code that implements these new consensus methods is in my tor branch on bug23826-23828 on GitHub: https://github.com/teor2345/tor.git The parent ticket for these related changes is #20916. The code changes are being tracked in #23826 and #23828, and the spec changes and proposal in #23898: https://trac.torproject.org/projects/tor/ticket/20916 If we've spoken about this, and I've left you out as an author, please let me know! Here is the proposal text: Filename: xxx-ipv6-in-micro-consensus.txt Title: Move IPv6 ORPorts from microdescriptors to the microdesc consensus Author: Tim Wilson-Brown (teor) Created: 18-Oct-2017 Status: Open Target: 0.3.3.x 1. Summary Moving IPv6 ORPorts from microdescs to the microdesc consensus will make it easier for IPv6 clients to bootstrap and select reachable guards. Since consensus method 14, authorities have voted for IPv6 address/port pairs (ORPorts) in "a" lines. Unreachable IPv6 ORPorts are dropped from the full consensus. But for clients that use microdescriptors (the default), IPv6 ORPorts are placed in microdescriptors. So these clients can only tell if an IPv6 ORPort is unreachable when a majority of voting authorities mark the relay as not Running. This proposal puts reachable relay IPv6 ORPorts in an "a" line in the microdesc consensus. This allows clients to discover unreachable IPv6 ORPorts, even if a minority of voting authorities set AuthDirHasIPv6Connectivity 1. 2. Proposal We add two new consensus methods, here represented as M and N (M < N), to be allocated when this proposal's implementation is merged. These consensus methods move IPv6 ORPorts from microdescs to the microdesc consensus. We use two different methods because this allows us to modify client code based on each method. Also, if a bug is discovered in one of the methods, authorities can be patched to stop voting for it, and then we can implement a fix in a later method. 2.1. Add Reachable IPv6 ORPorts to the Microdesc Consensus We specify that microdescriptor consensuses created with methods M or later contain reachable IPv6 ORPorts. 2.2. Remove IPv6 ORPorts from Microdescriptors We specify that microdescriptors created with methods N or later do not contain any IPv6 ORPorts. 3. Retaining Existing Behaviour The following existing behaviour will be retained: 3.1. Authority IPv6 Reachability Only authorities configured with AuthDirHasIPv6Connectivity 1 will test IPv6 ORPort reachability, and vote for IPv6 ORPorts. This means that: * if no voting authorities set AuthDirHasIPv6Connectivity 1, there will be no IPv6 ORPorts in the consensus, * if a minority of voting authorities set AuthDirHasIPv6Connectivity 1, unreachable IPv6 ORPort lines will be dropped from the consensus, but the relay will still be listed as Running, * if a majority of voting authorities set AuthDirHasIPv6Connectivity 1, relays with unreachable IPv6 ORPorts will be dropped from the consensus. We will document this behaviour in the tor manual page, see #23870. 3.2. Full Consensus IPv6 ORPorts The full consensus will continue to contain reachable IPv6 ORPorts. 3.3. Clients that use Full Descriptors Tor clients that use full descriptors already ignore unreachable IPv6 ORPorts, and have done so since at least 0.2.8.x. 4. Impact and Related Changes 4.1. Directory Authority Configuration We will work to get a super-majority (75%) of authorities checking relay IPv6 reachability, to avoid Running-flag flapping. To do this, authorities need to get IPv6 connectivity, and set AuthDirHasIPv6Connectivity 1. 4.2. Relays and Bridges Tor relays and bridges do not currently use IPv6 ORPorts from the consensus. We expect that 2/3 of authorities will be voting for consensus method N before future Tor relay or bridge versions use IPv6 ORPorts from the consensus. 4.3. Clients 4.3.1. Legacy Clients 4.3.1.1. IPv6 ORPort Circuits Tor clients on versions 0.2.8.x to 0.3.2.x check directory documents for ORPorts in the following order: * descriptors (routerinfo, available if using bridges or full descriptors) * consensus (routerstatus) * microdescriptors (IPv6 ORPorts only) Their behaviour will be identical to the current behaviour for consensus methods M and earlier. When consensus method N is used, they will ignore unreachable IPv6 ORPorts without any code changes. 4.3.1.2. IPv6 ORPort Bootstrap Tor clients on versions 0.2.8.x and 0.2.9.x are currently unable to bootstrap over IPv6 only connections when using microdescriptors. This happens because the microdesc consensus does not contain IPv6 ORPorts. When consensus method M is used, they will be able to bootstrap over IPv6 only connections using microdescriptors, without any code changes. 4.3.2. Future Clients 4.3.2.1. Ignoring IPv6 ORPorts in Microdescs Tor clients on versions 0.3.3.x and later will ignore unreachable IPv6 ORPorts once consensus method M or later is in use. (See #23827.) 4.3.2.2. IPv6 ORPort Bootstrap If a bootstrapping IPv6-only client has a consensus made with method M or later, it should download microdescriptors from one of the IPv6 ORPorts in that consensus. Previously, IPv6-only clients would use fallback directory mirrors to download microdescs, because there were no IPv6 ORPorts in the microdesc consensus. (See #23827.) 4.3.2.3. Ignoring Addresses in Unused Directory Documents If a client doesn't use a particular directory document type for a node, it should ignore any addresses in that document type. (See #23975.) 5. Data Size This change removes 2-50 bytes from the microdescriptors of relays that have an IPv6 ORPort, and adds them to reachable IPv6 relays' microdesc consensus entries. As of October 2017, 600 relays (9%) have IPv6 ORPorts in the full consensus. Their "a" lines take up 19 KB, or 33 bytes each on average. The microdesc consensus is 1981 KB, so this represents about 1% of its uncompressed size. Most tor clients are already running 0.3.1.7, which implements consensus diffs. We expect that most directory mirrors will also implement consensus diffs by the time 2/3 of authorities are voting for consensus method M. So we expect that this change will have a minimal impact, which is made even smaller by compression and consensus diffs. 6. External Impacts We don't expect this change to impact Onionoo and similar projects, because they typically use the full consensus. Metrics doesn't currently graph IPv6 usage in Tor, but would like to in future. -- Tim / teor PGP C855 6CED 5D90 A0C5 29F6 4D43 450C BA7F 968F 094B ricochet:ekmygaiu4rzgsk6n ------------------------------------------------------------------------
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