Re: IPv4 Address Flags

[Roy Marples <roy%marples.name@localhost>]

On 22/04/2015 01:48, Dennis Ferguson wrote:
> On 21 Apr, 2015, at 01:46 , Roy Marples <roy%marples.name@localhost> wrote:
>> As discussed here [1], a few people voiced their opinion that they
>> didn't like address removal when the carrier drops and would rather
>> re-negotiate at carrier up. The first step of doing this is to add IPv6
>> address flag semantics to IPv4 addresses.
> 
> To tell the truth I think this is fixing the problem in the wrong
> spot.  I don't see a big difference between unplugging the ethernet
> cable and plugging it back in, and unplugging the USB or Thunderbolt
> ethernet dongle and plugging it back in, or hot-swapping the ethernet
> line card out and replacing it with another.  If I have active protocol
> connections I would like them to survive the interface itself going
> away and coming back just as much as I would like them to survive
> the special case of the carrier dropping and coming back.  Adding
> complexity to deal only with the latter doesn't seem worth it.
> 
> I think it is better to let interface structures freely go and
> come and instead address the issue higher up.  A protocol session
> that is bound to a local address the box no longer has should no
> longer be allowed to actually send packets with that address but
> otherwise should be treated like it is getting ICMP unreachables in
> response to the packets it is (not) sending.  If the local address
> comes back it can pick up where it left off, if it doesn't it can
> time out or the user can close it or it can persist doing nothing,
> just like it would in the general case of the other end going
> unreachable.
> 
> This seems to work no matter what it is that goes away and comes
> back.

Agreed on all points.

But this is about Duplicate Address Detection which should (in my view
anyway) be done on each address on carrier up AND when an address is
added to the interface and the carrier is up. IPv6 does this, this patch
allows IPv4 to do it too.

Roy