Hello Ryan, or anyone else affected,

Accepted systemd into eoan-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/systemd/242-7ubuntu3.3
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-eoan to verification-done-eoan. If it does not fix
the bug for you, please add a comment stating that, and change the tag
to verification-failed-eoan. In either case, without details of your
testing we will not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: systemd (Ubuntu Eoan)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-eoan

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You received this bug notification because you are a member of Ubuntu
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https://bugs.launchpad.net/bugs/1671951

Title:
  networkd should allow configuring IPV6 MTU

Status in systemd:
  Unknown
Status in cloud-init package in Ubuntu:
  Confirmed
Status in netplan.io package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in cloud-init source package in Bionic:
  Confirmed
Status in netplan.io source package in Bionic:
  Fix Released
Status in systemd source package in Bionic:
  In Progress
Status in cloud-init source package in Disco:
  New
Status in netplan.io source package in Disco:
  Fix Released
Status in systemd source package in Disco:
  Won't Fix
Status in cloud-init source package in Eoan:
  New
Status in netplan.io source package in Eoan:
  Fix Released
Status in systemd source package in Eoan:
  Fix Committed
Status in cloud-init source package in Focal:
  Confirmed
Status in netplan.io source package in Focal:
  Fix Released
Status in systemd source package in Focal:
  Fix Released

Bug description:
  = netplan.io =

  [Impact]

   * IPv6 traffic failing to send/receive due to incompatible/low MTU
  setting. Specifically, IPv6 traffic may have higher MTU requirements
  than IPv4 traffic and thus may need to be overridden and/or set to a
  higher value than IPv6 traffic.

  [Test Case]
   * Apply a netplan configuration that specifices ipv6-mtu:

  network:
    version: 2
    ethernets:
      eth0:
        dhcp4: true
        dhcp6: true
        ipv6-mtu: 6000

   * Check that MTU bytes, is at least IPv6MTUBytes on the interface:

  $ sysctl net.ipv6.conf.eth0.mtu
  net.ipv6.conf.eth0.mtu = 6000

  [Regression Potential]

   * This is a future compatible backport of an additional keyword not
  used by default. It may result in MTU change to a higher value, which
  should not cause loss of connectivity.

  [Other Info]

   * Original bug report below

  = end of netplan.io =

  = systemd =

  [Impact]

   * IPv6 traffic failing to send/receive due to incompatible/low MTU
  setting. Specifically, IPv6 traffic may have higher MTU requirements
  than IPv4 traffic and thus may need to be overridden and/or set to a
  higher value than IPv6 traffic.

  [Test Case]

   * Use IPv6MTUBytes= setting in a .network unit
   * Restart systemd-network
   * Check that there no error messages / warnings about not-recognizing this 
option
   * Check that MTU bytes, is at least IPv6MTUBytes on the interface

  [Regression Potential]

   * This is a future compatible backport of an additional keyword not
  used by default. It may result in MTU change to a higher value, which
  should not cause loss of connectivity.

  [Other Info]

   * Original bug report below

  = end of systemd =

  1) Zesty
  2) systemd-232-19
  3) I need to configure the IPV6 MTU for tunneling by adding an 
IPv6MTUBytes=1480 value in the .network file for an interface with an IPV6 
static address in the [Network] section
  4) networkd does not parse or read the value and does not apply this 
configuration to the interface.

  Upstream has discussed this issue here:

  https://github.com/systemd/systemd/pull/1533

  But it's been closed in favor of only setting via RA.

  However, we know of multiple use-case which are currently supported in
  ifdupdown where we want to retain control over IPV6 MTU values outside
  of PMTU Discovery configurations.

  Some context from those discussions

  >> Client systems that route their ipv6 packets to a 6in4 router also
  >> have to have their ipv6 mtu lowered.  They could lower their link mtu,
  >> so their ipv6 packets are small enough, but that reduces performance
  >> of their ipv4 network.

          Yes.  Anything that creates a PMTUD black hole can result in
  situations where the higher header overhead of IPv6 will cause IPv4 to
  pass but IPv6 traffic to be dropped.

          One example here is egress from an ipsec tunnel wherein the next
  hop MTU is too low for IPv6 datagrams to pass.  Another is VM ->
  whatever -> host bridge -> tunnel ingress.  If the datagram cannot enter
  the tunnel due to size, it is dropped, and an ICMP response uses the
  tunnel address as a source, which may not be routable back to the
  origin.  This one is an issue with IPv4 as well, and is one case where
  manually setting the IPv6 MTU lower than the (also manually set) device
  MTU is of benefit.

          In essence, any of these sort of cases that require an explicit
  setting of the device MTU will likely require a setting of the IPv6 mtu
  as well to account for its larger header overhead.

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