[Bug 1391662] Re: mount.nfs does not downgrade NFS version when connecting to dual-stack NFS server

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Title:
  mount.nfs does not downgrade NFS version when connecting to dual-stack
  NFS server

Status in “nfs-utils” package in Ubuntu:
  In Progress

Bug description:
  If you attempt to mount a share from a server that is dual stack (i.e.
  has both an A and a AAAA record in DNS) and NFSv3-only, mount.nfs goes
  into an infinite loop of retrying an NFS-v4 mount:

  mount nfs-v3-server:/path /mnt -v
  mount: no type was given - I'll assume nfs because of the colon
  mount.nfs: timeout set for Tue Nov 11 14:25:34 2014
  mount.nfs: trying text-based options 'vers=4,addr=x.x.x.x,clientaddr=x.x.x.x'
  mount.nfs: mount(2): Protocol not supported
  mount.nfs: trying text-based options 'vers=4,addr=xxxx:xxxx::xxxx,clientaddr=xxxx:xxxx::xxxx'
  mount.nfs: mount(2): No route to host
  mount.nfs: trying text-based options 'vers=4,addr=x.x.x.x,clientaddr=x.x.x.x'
  mount.nfs: mount(2): Protocol not supported
  mount.nfs: trying text-based options 'vers=4,addr=xxxx:xxxx::xxxx,clientaddr=xxxx:xxxx::xxxx'
  mount.nfs: mount(2): No route to host

  If we "hide" the AAAA record by setting an override in /etc/hosts,
  then mount.nfs correctly retries with NFSv3:

  mount -t nfs nfs-v3-server:/path /mnt -v
  mount.nfs: timeout set for Tue Nov 11 15:01:35 2014
  mount.nfs: trying text-based options 'vers=4,addr=x.x.x.x,clientaddr=x.x.x.x'
  mount.nfs: mount(2): Protocol not supported
  mount.nfs: trying text-based options 'addr=x.x.x.x'
  mount.nfs: prog 100003, trying vers=3, prot=6
  mount.nfs: trying x.x.x.x prog 100003 vers 3 prot TCP port 2049
  mount.nfs: prog 100005, trying vers=3, prot=17
  mount.nfs: trying x.x.x.x prog 100005 vers 3 prot UDP port 635
  nfs-v3-server:/path on /mnt type nfs (rw)

  ProblemType: Bug
  DistroRelease: Ubuntu 12.04
  Package: nfs-common 1:1.2.5-3ubuntu3.1
  ProcVersionSignature: Ubuntu 3.2.0-70.105-generic 3.2.63
  Uname: Linux 3.2.0-70-generic x86_64
  ApportVersion: 2.0.1-0ubuntu17.8
  Architecture: amd64
  Date: Tue Nov 11 15:56:25 2014
  InstallationMedia: Ubuntu-Server 10.04.2 LTS "Lucid Lynx" - Release amd64 (20110211.1)
  MarkForUpload: True
  ProcEnviron:
   SHELL=/usr/bin/ksh
   TERM=xterm
   PATH=(custom, no user)
   LANG=en_US
  SourcePackage: nfs-utils
  UpgradeStatus: Upgraded to precise on 2013-10-07 (400 days ago)

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