[tor-bugs] #33618 [Core Tor/Tor]: Add IPv6 Support to is_local_addr()

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#33618: Add IPv6 Support to is_local_addr()
---------------------------------+------------------------------
 Reporter:  kimimaro             |          Owner:  (none)
     Type:  enhancement          |         Status:  new
 Priority:  Medium               |      Component:  Core Tor/Tor
  Version:                       |       Severity:  Normal
 Keywords:  outreachy-ipv6 ipv6  |  Actual Points:
Parent ID:                       |         Points:
 Reviewer:                       |        Sponsor:
---------------------------------+------------------------------
 "  We propose this optional change, to improve the accuracy of IPv6
 address
    detection from directory documents.

    Directory servers use is_local_addr() to detect if the requesting tor
    instance is on the same local network. If it is, the directory server
 does
    not include the X-Your-Address-Is HTTP header in directory documents.

    Currently, is_local_addr() checks for:
      * an internal IPv4 or IPv6 address, or
      * the same IPv4 /24 as the directory server.

    We propose also checking for:
      * the same IPv6 /48 as the directory server.

    We choose /48 because it is typically the smallest network in the
 global
    IPv6 routing tables, and it was previously the recommended per-customer
    network block. (See [RFC 6177: IPv6 End Site Address Assignment].)

    Tor currently uses:
      * IPv4 /8 and IPv6 /16 for port summaries,
      * IPv4 /16 and IPv6 /32 for path selection (avoiding relays in the
 same
        network block).
    See also the next section, which uses IPv6 /64 for sybils."
 Source: https://gitweb.torproject.org/torspec.git/tree/proposals/312
 -relay-auto-ipv6-addr.txt#n1099

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33618>
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