DHCP versus DHCPv6 Release behaviour

[Ross Chandler]

> On 7 Aug 2017, at 07:34, Ola Thoresen <ola at nlogic.no> wrote:
> 
> Technically, the server is correct in that after a "release" is received, it is free to assign the address to another client, and as such, the client should not expect to receive the same address on the next assignment. 
> However, following the principle of least surprise, I agree that the user probably expects to receive the same address, especially if they are just changing some settings on the wan interface. 
> 
> If you are free to change both server and client behavior, I believe a combination of 2 and 4 is probably the "most correct" solution. 
> The client should probably send a release both for v4 and v6 at the same time. 
> But on the other hand, it would be nice if the server would remember the previous lease, at least for a while, and reassign it to the client if another request comes in within a reasonable time. 


Yes, option 5 might be “2+4”. In options 2 & 5 to avoid a change in service level for IPv4 the DHCP server would also need to remember the IPv4 lease for a period long enough to keep the address the same after the Release followed shortly afterwards by a Discover.  That is a configuration option at my DHCP server. The IPv4 pools, unlike the large IPv6 prefix pools, are run pretty hot close to capacity to maximise the v4 pool utilisation. 

Ross 

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