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

[Tore Anderson]

Public bug reported:

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

** Affects: ifenslave-2.6 (Ubuntu)
     Importance: Undecided
         Status: New

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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:
  New

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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