Re: Detached address check

["Robert Swindells" <rjs%fdy2.co.uk@localhost>]

On Wed, November 22, 2017 11:49 am, Roy Marples wrote:
> On 21/11/2017 10:02, Robert Swindells wrote:
>> On Tue, November 21, 2017 9:26 am, Roy Marples wrote:
>>> On 18/11/2017 13:37, Robert Swindells wrote:
>>>> On Fri, November 17, 2017 4:57 pm, Robert Swindells wrote:
>>>>> I feel that the changes made to check whether a sending address is
>>>>> valid
>>>>> are too strict.
>>>>>
>>>>> The check means that an attempt to connect from the address of an
>>>>> interface that is marked detached to the same address will fail even
>>>>> though there is still a route for this address to the loopback
>>>>> device.
>>>>>
>>>>> The change was introduced in:
>>>>>
>>>>> <http://mail-index.netbsd.org/source-changes/2016/09/15/msg077726.html>
>>>>
>>>> To clarify, I expect to be able to do:
>>>>
>>>> # ifconfig wm0 inet 192.168.0.1 netmask 0xffffff00 up
>>>> # ping 192.168.0.1
>>>>
>>>> and for it to work every time, not just when wm0 has detected a
>>>> carrier. In the traditional usage, the packets don't go through wm0
>>>> anyway they go through lo0.
>>>
>>> Aside from ping, what else do you really want?
>>
>> I want all network programs to work.
>>
>>>>
>>>> The RFC 4862 referenced in the commit is for IPv6, I don't think that
>>>> IPv4 behaviour should change too.
>>>>
>>>> I'm not even convinced that I want this behaviour for IPv6, I would
>>>> prefer that addresses set using ifconfig(8) should stay valid until
>>>> I change them.
>>>
>>> What would you actually do with them though?
>>> You have localhost - 127.0.0.1 which works just fine.
>>
>> I shouldn't need to use localhost to connect to the same machine, that
>> isn't the way that UNIX networking has traditionally worked, there
>> wouldn't be any need for the route from each interface address to lo0
>> if we adopt your new programming model.
>
> That's a fair comment.
> I've attached a patch which should fix this for IPv4 at least.
> I'll work on the IPv6 side later.

I will look at your patches.

>> I feel that setting DETACHED/TENTATIVE based on link status should
>> be removed from IPv4 altogether. I have commented it out in my tree
>> and my machine is working again.
>>
>> For IPv6, I would enable it with a sysctl whose value is only set to
>> true when ipv6mode="autohost".
>
> So you don't want in kernel Duplicate Address Detection?
> We already have sysctls to set the DaD packets sent to zero which
> effectively addresses the TENTATIVE part. The above patch handles
> DETACHED (well, for IPv4 anyway).

I'm not in the habit of assigning duplicate IPv4 addresses so don't
really care about DaD. That isn't the question that I'm asking though.

I don't see why a router that isn't using stateless address autoconfig
on a downstream interface should get the address of that interface set
to DETACHED if the cable is unplugged.

Also, which RFC requires that IPv4 should follow the same protocol ?

>> If this change makes it into NetBSD-8 then I think you are going to
>> spend a lot of time answering user questions.
>
> Well, the change has been in -current for over 2.5 years and I've not
> spent much time either answering question or fixing bugs with it so I
> disagree with that somewhat sweeping statement.

The final change was only in September 2016, there are plenty of people
still using NetBSD-7 on the mailing lists.

Robert Swindells