[Bug 1288196] Re: MAC address of bonding interface is randomly picked

[Tore Anderson]

For what it's worth, we never had any problem with the old style
"bond_master eth0 eth1" syntax. On a server, typically all the slaves
will become available pretty much at the same time during the boot
process - devices hot-plugged at a later time is generally not the use
case you'd need to optimise for. So waiting until the primary slave
appears before setting up the bonding interface seems to me to be a
perfectly adequate way to handle this .

Tore

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https://bugs.launchpad.net/bugs/1288196

Title:
  MAC address of bonding interface is randomly picked

Status in “ifenslave-2.6” package in Ubuntu:
  Triaged

Bug description:
  The new style of bonding configuration (using "iface bond0 [...] \
  bond_slaves none" for the master interface plus "iface ethX inet
  manual \ bond_master bond0" for each slave interface) results in the
  MAC address of the bond0 interface being randomly picked from one of
  the slaves.

  This causes problems for auto-configuration methods such as IPv4 DHCP
  and IPv6 SLAAC, as DHCPv4 leases and IPv6 Interface Identifiers are
  directly based on the interface's MAC address. This means that if the
  MAC address changes unexpectedly, so may the IP address(es) as well,
  which might be big problem if the machine in question is some sort of
  server or similar that have just rebooted.

  Unexpected MAC address changes may also cause problems for statically
  configured addresses, as the upstream router will likely have cached
  the IPv4 ARP and/or the IPv6 Neighbour entry pointing to the old MAC
  address. This results in the server not having any network
  connectivity until the upstream router have timed out its cache entry
  and probes anew. These timeouts may well be up to 20 minutes.

  The old configuration style ("iface bond0 [...] \ bond_slaves eth0
  eth1 [...]") did not have this problem, as the MAC address used for
  bond0 would always be the first listed interface (eth0). While I have
  no particular objection to the syntax change in itself, the choice of
  MAC address should be deterministic. It is probably possible to
  manually set the MAC address with the "hwaddr" option, but this is not
  ideal because it by necessity means every node must have a unique
  configuration file, which is problematic for large automated server
  deployments for example.

  Tore

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