Dnscache

Simple DNS proxy supporting one upstream. Designed for using slow and unreliable upstream DNS servers like Tor's DNS resolver. Trades consistency for availability. Not for serious use.

License = MIT or Apache 2.0

There are some pre-built versions on Github releases. Versions further than 0.1.2 have no command-line-user-facing benefits yet.

DNSCache can also be used as a library (with your own database and network abstraction, but with DNS packets still as byte blobs).

``` dnscache 0.1.3 Vitaly _Vi Shukela vi0oss@gmail.com Simple DNS cacher.

USAGE: dnscache [OPTIONS]

FLAGS: -h, --help Prints help information -V, --version Prints version information

OPTIONS: --max-ttl Maximum TTL of A or AAAA entry, seconds [default: 4294967295] --min-ttl Minimum TTL of A or AAAA entry, seconds [default: 0] --neg-ttl Negative reply TTL, seconds [default: 30]

ARGS: Listen address and port Upstream DNS server address and port Path to LevelDB database directory ```

Features:

• IPv6 AAAA records
• Forwarding of trickier queries as is
• Multi-question queries
• Minimal protection from poisoning by filtering domain names in replies
• Always tries to immediately return some A or AAAA records for client to try, no waiting for refreshing.
• Clamping TTL betwen user-specified min and max (the cache contains unmodified value).

Notes:

• It does not construct DNS requests on its own, it reuses client-constructed packets
• Uncached queries (non-A, non-AAAA or non-IN) are forwarded based in ID
• TTL may be 0 in replies
• Single threaded, single UDP socket
• If all A or AAAA entries disappear in reply, cached ones retain instead. AAAA resolution sometimes works in Tor DNS resolver, sometimes not.
• CNAMEs are resolved recursively into A/AAAA entries and are not persisted
• Unsupported queries (MX, All) are forwarded as-is based on ID only

Concerns:

• Entries are never deleted from cache
• If data is stale, it first replies with TTL 0, then re-checks in upstream
• The used LevelDB implementation is not recommended for serious use yet.
• The same socket used both for client and for upstream communication. Can't listen only on 127.0.0.1, but rely on 8.8.8.8.

Database format: LevelDB database with domain names like internals.rust-lang.org as keys and CBOR as values. Sample value:

``` {"a4": {"t": 1513810855, "a": [{"ttl": 599, "ip": h'4047a8d3'}]}, "a6": {"t": 1513810855, "a": [{"ttl": 599, "ip": h'20010470000103a80000000000000211'}]}}

00000000 a2 62 61 34 a2 61 74 1a 5a 3a eb a7 61 61 81 a2 |.ba4.at.Z:..aa..| 00000010 63 74 74 6c 19 02 57 62 69 70 44 40 47 a8 d3 62 |cttl..WbipD@G..b| 00000020 61 36 a2 61 74 1a 5a 3a eb a7 61 61 81 a2 63 74 |a6.at.Z:..aa..ct| 00000030 74 6c 19 02 57 62 69 70 50 20 01 04 70 00 01 03 |tl..WbipP ..p...| 00000040 a8 00 00 00 00 00 00 02 11 |.........| 00000049 ```

Simple description:

{"a4": {"t": timestamp_unix, "a":[IPv4/TTL pairs list]}, "a6": null (for never requested values)} {"t": ..., "a":[(empty list)]} means negatively cached

The format is subject to change and is other than one used by pre-build 1.2 binaries.