DNS statistics from node operators

Jacob Appelbaum jacob at appelbaum.net
Wed Jun 3 19:28:40 UTC 2009

Olaf Selke wrote:
> Jacob Appelbaum wrote:
>> I'm looking into some simple DNS related statistics in the Tor network.
>> Specifically, I wrote a small patch that tells an operator the total
>> number of cached entries for their node. I'd like to know about your DNS
>> cache size, especially if you run a fast node!
> how does tor dns caching work? My exit gw's tor process size increases
> by about 50 MB each TB of tor traffic.

Generally speaking, your Or will cache a couple of record types when
people use you to resolve names (A, PTR). You'll keep them cached for a
maximum amount of time (defined in the source code) or less time
depending on the returned TTL. Generally, your OR resolves names when
someone extends a circuit through you for a connection or when they
explicitly use your node for name resolution.

I was actually hoping to get statistics from you specifically, so I'm
glad that you responded!

Please let us know how large your cache gets? It would be interesting to
see the average size of the cache for the top twenty nodes.

My node 'trusted' for example certainly does not have 50MB of entries:
Jun 03 21:20:51.271 [notice] Our DNS cache has 28 entries.
Jun 03 21:20:51.271 [notice] Our DNS cache size is approximately 9856 bytes.

My exit policy on 'trusted' allows *:53. Simply being able to resolve
names doesn't increase my cache size too much.

Badbits on the other hand does allow a few other ports and today, it has
a much larger cache:
Jun 03 14:26:37.577 [notice] Our DNS cache has 3473 entries.
Jun 03 14:26:37.577 [notice] Our DNS cache size is approximately 1104968


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