DHCP Reservations

[Roger Heflin]

On both a dd-wrt and a recent asus router I have successfully got the
older bonding module to bring up wireless and wired in a
active/passive mode (wired is active if there).      Both interfaces
would have the same IP and mac address and I can unplug the wired and
immediately have it switch over to wireless with no obvious drops.
I can also switch back to a wired connection with no drops (usually
done in the middle of a big data transfer to speed it up).     This is
outside of network manager, and was a major pain to get it working
consistently after a reboot, but I believe it now works consistently
on reboots.    I believe the bonding module does force arps when it
switches interfaces.

On Tue, Feb 3, 2015 at 8:37 AM, Andrew R Paterson
<andy.paterson at ntlworld.com> wrote:
> On Wednesday 04 February 2015 00:55:29 Tim wrote:
>> Jim Lewis wrote:
>> >> Quick question about DHCP reservations: I have laptops with both
>> >> wired and wireless NICs, is it okay to have the router assign the
>> >> same IP to both interface?
>>
>> I wrote:
>> > I seem to recall being able to do that, with the DHCP server on my
>> > Fedora Core 4 installation (having two separate MAC matching clauses
>> > that applied the same IP).  Other servers may try to prevent you doing
>> > that, as it can be problematic.
>>
>> Just following up, since I wasn't clear.  My comment was along the same
>> lines as the original poster, trying to see what would happen if I
>> assigned the same IP to wireless or wired network interfaces on my
>> laptop, where only one of them would be active at any one time.
>>
>> The reason I tried, was that it was annoying having changing addresses,
>> one way or another.  Whether that was the IP address, or the named
>> address attached to the current IP.
>>
>> For instance, my hostname might be wired.example.com or
>> wireless.example.com, because the IP changed.  Either change brought
>> about their own set of nuisances.
>>
>> And, no, the common Fedora approach of associating your desired machine
>> hostname against 127.0.0.1 is not a sensible alternative, either.
>>
>> Having multiple interfaces is a nuisance, and the best I could come up
>> with was having to use the GUI to manually disconnect one device or the
>> other, not letting any automatic system attempt it.
>>
>> A whole slew of other problems came about should both interfaces be up
>> and active at the same time.
> Surely "hot-swapping" IP addresses between interfaces wont work very well,
> since forgetting DHCP its ARP that will cause a problem.
> Each previously communicating host will have a MAC address logged in its ARP
> table for the offending IP address.
> If the IP address changes MAC addresses, the ARP entries on all other hosts
> must time-out in order to be renewed via an ARP broadcast.
>
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