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[William Grant <me@xxxxxxxxxxxxxxxxxx>]

** No longer affects: dnsmasq

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https://bugs.launchpad.net/bugs/1542597

Title:
  dnsmasq breaks Steam downloads on Comcast

Status in dnsmasq package in Ubuntu:
  New

Bug description:
  TL;DR: With dnsmasq configured, "nslookup
  cdn.cs.comcast.steampowered.com" (rather, the query, not nslookup
  itself) hangs.  As a result of the DNS query hanging, Steam is unable
  to download any game content.

  Longer explanation, which I posted on the Steam forum at
  http://steamcommunity.com/discussions/forum/1/412446292762583371/ to
  help other users:

  I had a persistent problem with Steam not downloading games on Ubuntu,
  even on the same machine and same network where it worked fine under
  Windows (both 7 and 10). Here's an explanation of why and how to fix
  it, since most people will not be able to diagnose it.

  Background:

  Like most big data providers, Steam has a lot of servers hosted at
  various ISPs. When you download a game, you're directed to servers
  that are topologically closer to you--usually ones hosted by the ISP
  you use. In my case, this is Comcast, and Steam uses the host name
  cdn.comcast.cs.steampowered.com.

  Ubuntu Desktop uses a caching DNS server called dnsmasq. Besides
  providing caching services, it captures advertised hostnames on the
  network, allowing you to refer to other machines by name without
  having to set up DNS.

  Symptom:

  You'll get dialog windows and messages in the Steam log file saying
  that connections timed out. No downloads will actually work.

  Interestingly, nowhere does it explicitly tell you that it's actually
  the DNS query that's timing out, as opposed to the connection to the
  actual content server. This confused me quite a bit.

  The problem:

  Steam's DNS and dnsmasq don't get along. The list of DNS records for
  cdn.comcast.cs.steampowered.com is long enough that the response
  doesn't fit in a UDP packet. Normally this is retried transparently
  over TCP and works fine. However, dnsmasq stalls and times out on this
  request. (Don't ask me why. I haven't debugged it--yet.) As a result,
  all attempts to connect to the Steam content servers fail, and no
  downloads occur.

  Note: I've only run the Steam client on Ubuntu 14.10 and 15.04. I do
  not know whether this problem affects other versions.

  Workaround:

  The obvious workaround is to stop using dnsmasq. However, it's
  somewhat hardwired into Ubuntu. Here's what I did:

  # apt-get install unbound # do this first or you'll be sad
  # cd /etc/NetworkManager
  # service NetworkManager stop
  # vi NetworkManager.conf # or whatever editor you want; I don't care
  [change "dns=dnsmasq" to "dns=unbound"]
  # rm /etc/resolv.conf # don't forget this
  # service NetworkManager start

  Now all your DNS queries should go through your local unbound server
  (at 127.0.0.1 a.k.a. localhost), retries over TCP should work as
  expected, and Steam should be able to download just fine. You can test
  it with:

  # nslookup cdn.comcast.cs.steampowered.com

  If that hangs or returns SERVFAIL or REFUSED, you still have a
  problem.

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