same link-local address on multiple interface and OSPFv3

[Phil Mayers]

On 06/28/2013 09:07 PM, Brian E Carpenter wrote:
> On 29/06/2013 00:41, Mikael Abrahamsson wrote:
>> On Fri, 28 Jun 2013, Matjaž Straus Istenič wrote:
>>
>>> Workaround is rather simple: use different link-local addresses on
>>> IPv6-enabled interfaces and you are safe. But, nevertheless, I think
>>> using same link-local pairs on links should not get you into any
>>> trouble, right?
>>
>> Correct, the same way that configuring fe80::1 on one interface and
>> fe80::2 on a second interface, and on this second interface the other
>> end should be able to have fe80::1 as its address, and everything should
>> work fine. Everything else is buggy, as you already have concluded.
>
> Dumb question: would the same product fail if you configured 10.1.1.1

Many routers wouldn't let you do that in IPv4. Cisco IOS doesn't, for 
example:

core-spare(config)#int vl100
core-spare(config-if)#ip address 10.1.1.1 255.255.255.0
core-spare(config-if)#no shut

core-spare(config)#int vl101
core-spare(config-if)#ip address 10.1.1.1 255.255.255.0
% 10.1.1.0 overlaps with Vlan100

...and IOS then forbids me from "no shut"ing vl101:

core-spare(config-if)#int vl101
core-spare(config-if)#no shut
% 10.1.1.0 overlaps with Vlan100
Vlan101: incorrect IP address assignment


> on two different IPv4 interfaces? (If yes, it tells you there is some
> sloppy basic design.) (And yes, I realise that the two OSPFs might have
> completely independent code bases.)

OSPFv3 is also different at the protocol level to OSPFv2.