[tor-dev] Proposal 312: Automatic Relay IPv6 Addresses

[s7r]

Hi again,

Apologies, a quick follow-up:

There is another RFC (older), that is in use by Debian apparently:
RFC3041. https://tools.ietf.org/rfc/rfc3041.txt

From:
https://manpages.debian.org/buster/iproute2/ip-address.8.en.html
see `mngtmpaddr`

RFC4941 is newer and with some improvements, however it does not mention
its purpose is to update / deprecate RFC3041. Actually it mentions the
differences / improvements.

Anyway, the point still fully stands, I just thought both RFCs should be
mentioned. Bottom line still is temporary (expiring) but otherwise
public and reachable IPv6 addresses in relay descriptor.


s7r wrote:
> Hi teor,
> 
> Thanks for this epic work, some lecture for me to deeply go over this
> weekend.
> 
> By briefly reviewing I've noticed something important is missing that
> should be a part of this proposal.
> 
> I am not sure under which section it should go under. I guess `3.2.2.
> Use the Advertised ORPort IPv4 and IPv6 Addresses`, or maybe it's
> important enough that we should make its own section.
> 
> In IPv6, besides publicly routable and non-publicly routable addresses
> (fe80:// etc.) which are documented in the proposal, we have temporary
> IPv6 addresses coming from Privacy extensions or RFC4941 IPv6 addresses.
> 
> https://tools.ietf.org/rfc/rfc4941.txt
> 
> These addresses are publicly routable, they can appear as reachable from
> the directory authorities or from directory data fetches, but they have
> limited lifetime and change over time. I am not sure if one  such
> address becomes deprecated if already in use (say by Tor), as the RFC
> states MAY _if not in use by applications  or upper layers_:
> 
>    "As an optional optimization, an implementation MAY remove a
>    deprecated temporary address that is not in use by applications or
>    upper layers as detailed in Section 6."
> 
> But since this is implementation dependent, we cannot be sure about the
> behavior across different platforms that relays might run on.
> 
> It is up to the operating system if such addresses are used or not. In
> Debian they are disabled by default net.ipv6.conf.eth0.use_tempaddr=0
> (unless some desktop packages that use network manager with different
> settings change it). In Windows (at least Windows 10) apparently they
> are enabled by default.
> 
> The question is, do we want such addresses in relay descriptors? I think
> such addresses will behave similar to dynamic IPv4 addresses, or even
> worse since these ones really change when they want, not just when we
> disconnect and reconnect the network interface. So maybe Tor should
> detect such behavior and log an error or something?
> 
> Actually I'll setup a vm this weekend and give it a native, static /64
> IPv6 prefix, enable privacy extension to use temporary addresses and
> spin up a Tor process on it. Then disconnect the internet a couple of
> times and see how it behaves, how often it changes.
> 
> What do you think?
> 

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