IPv6 duplicate address detection

[Bob Van Zant]

On 5/6/09 3:06 PM, "JINMEI Tatuya / 神明達哉" <Jinmei_Tatuya at isc.org> wrote:
> I'm afraid we need clarification first...what do you mean by
> "reconfigure an interface with an IPv6 address"?  Do you mean adding a
> new IPv6 address to an interface?  If so, I'm not sure why you
> referred to the following part of RFC2461 (btw the RFC was updated by
> RFC4861):
We have a crude form of NIC pairing in our software. We allow someone to
logically pair two interfaces together. This is implemented by `ifconfig
down` both interfaces, configure them both the same, then `ifconfig up` the
primary interface. We then monitor the link state of the primary interface.
If the state goes to down, we `ifconfig down` the primary NIC and then
`ifconfig up` the secondary NIC. This has the effect of changing the link
layer address associated with a given IPv6 address. After we do this we send
out the unsolicited NA to update whatever switch we're plugged into.

We do this today with IPv4 and ARP and it works fine.

>> [1] RFC 2461 section 7.2.6 paragraph 1:
>> 
>>    In some cases a node may be able to determine that its link-layer
>>    address has changed (e.g., hot-swap of an interface card) and may
>>    wish to inform its neighbors of the new link-layer address quickly.
> 
> this example talks about the case where the link-layer address changes
> for an existing address, not where a new address is configured.

I hope the example I gave above helps to clarify that I am trying to handle
a case where the link-layer address has changed. However, I'll admit that I
had been planning on sending the unsolicited NA after any ifconfig commands
were executed. So long as I'm not flooding the network it doesn't seem
harmful and potentially seems useful to avoid a few seconds of downtime
while the network figures things out.

-Bob