[tor-relays] excessive bandwidth assigned bandwidth-limited exit relay

Dhalgren Tor dhalgren.tor at gmail.com
Thu Oct 1 20:10:55 UTC 2015

On Thu, Oct 1, 2015 at 7:45 PM, Steve Snyder <swsnyder at snydernet.net> wrote:
> Another consumer of bandwidth is name resolution, if this is an exit node.  And the traffic incurred by the resolutions is not reflected in the relay statistics.
> An exit node that allocates 100% of it's bandwidth to relaying traffic will starve the resolver, and vice versa.

Absolutely true where physical bandwidth is the limiting factor.

However please note this thread/topic is explicitly in regard to
relays that have unconfined gigabit Ethernet connectivity in excellent
capacity networks, but that must limit bandwidth consumption in order
to avoid billing-plan overuse charges.

Loss of DNS resolver traffic is not a concern here.

In this specific case it appears that the Tor bandwidth allocation
system "over rates" subject relays to the point where the relays will
internally apply rate-limit throttling, thereby degrading end-user
latency.  This is not optimal and is undesirable.

As stated earlier in this thread, if the consensus weight of the relay
in question does not moderate within a few days and unless a better
idea materializes, an IPTABLES packet-dropping rate limit will be
applied.  This will cause the under-utilized gigabit connection to
behave similarly to a heavily utilized lower-bandwidth connection.
This should result in a lower authority rating that does not saturate
the relay, while still making use of the intended amount of bandwidth.

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