Link flap for setting ether/MAC address

[Hiroki Sato]

Anish <akgupt3 at gmail.com> wrote
  in <CALnRwMR7qKqzq3j8-YGOAFhZN-u6g1o=s4LjnsLJZ1x=oRAHAw at mail.gmail.com>:

ak> Hi all,
ak> Got a very basic question, why physical link is flapped when we set the
ak> address
ak>
ak> # dmesg -c
ak> # ifconfig ix1 ether 70:6d:15:1f:12:72
ak> ..wait..
ak> # dmesg
ak> ix1: link state changed to DOWN
ak> ix1: link state changed to UP
ak> #
ak>
ak> is this a bug or expected behavior? We could update our MAC in next ARP
ak> request without link flap or some other system like switch etc expect the
ak> link flap to update ARP. Is this the behavior for other systems?

 I think this depends on the driver.  Some drivers reset the NIC when
 the MAC address is changed mostly because it is an easy way to
 re-configure the multicast filtering rules or the other settings
 which must be updated for the new MAC address.  It causes a link
 flap.  For upper layers above the NIC driver, you are correct.

-- Hiroki
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