dhcpcd-discuss

On 04/05/2016 14:25, Shahid Mahmood wrote:
> Hi
> We have a scenario where we request a custom option, and if the DHCP
> server understands the option it returns an offer filled with the value
> (the "better" offer). If not, we accept whatever server sends us (the
> 'simple' offer).
> 
> But in some cases, there are two servers. One sends the "better" offer
> slightly later (say 1 sec) than the simple offer. We end up using the
> 'simple' offer.
> 
> Is it possible to pick the "better" offer even if it comes after a short
> period (1 sec) later than the 'simple' one?

Well, there are many aspects of "better".
Generally DHCP servers on the same network segment should be configured
the same, just with different pools.

> Thoughts:
> a) "require" the custom option with -Q. If no offer is received within
> certain time, retry without -Q Side effect: delay for networks without
> custom option.
> b) Somehow fireup two parallel instances, one with -Q. Then deal with
> the lease. (not even sure if this is possible)
> c) Patch dhcpcd (would like to avoid this)

d) "preferred" option list, similar to -Q, but adds weight to a message.
This option would cause dhcpcd to stall for reboot timeout seconds until
DHCP DISCOVER is replied to with all preferred options.
Upon timeout the received replies would be sorted by preferred option
availability (not option value) and dhcpcd will then bind to this server.
Once bound it stays bound and will not prefer a "beter" server until the
lease is dropped (expired, carrier, release for example).

This probably won't be trivial to do in the very near future.

Roy