dhcpcd-discuss

Hi

On 14/02/2014 7:05, Jyothsna Rajan wrote:
> I use dhcpcd_5.2.12 on my devices , running linux, to obtain DHCP IP.
> I have been testing the switch-over from DHCP to link local on loss of
> network connectivity and vice-versa when connectivity is restored. I
> found that it takes >8mins for the address to change from DHCP to link
> local and 2-3 mins to change from link-local to DHCP.
>
> I am using the dhcpcd.conf(5) file as available with the source.
> I invoke the client with following command:
> dhcpcd -q --reboot 0 --hostname "" -t 16 <ifname>
>
> DHCP server is authoritative and lease-time is set to 600.
>
> I have the following questions:
> 1. Once a valid DHCP address has been obtained, does the client
> take-no-action-but-wait until the lease renewal time has expired ?
>
>  2. What IP will the device have if someone disconnects the device in
> the interval after a DHCP address has been obtained but before its
> time to renew the lease? Will the device retain its DHCP IP until it
> is time to renew at which time dhcpcd "wakes up" and detects there is
> no connection and obtains a link local address?
> 3. How can I force dhcpcd to monitor connection status and switch to
> link-local soon as a loss of connection is detected? Can I use the
> "NOCARRIER" reason to detect connection status and invoke a hook
> script to force change to link-local address?
>  4. Similarly, for the case where a device having link-local address
> is connected back into a network, is there any configuration parameter
> that I can tweak to reduce the time taken to switch back to DHCP
> address?
> 5. Will reducing the DHCP lease time setting help? If so, what is the
> minimum value I can set without jeopardizing any other functionality?
> I haven't been able to try this because the server is company wide and
> i cannot reboot it on a working day.

1. dhcpcd does take action when the kernel reports network connection 
goes down/up
2. it will start with none. with your config it will discover, timeout 
after 30 seconds [1] and then negotiate a link local address.
3. it should do this. You cannot force an address change from the 
commandline, just a reconfigure.
4. when a link local address is configured, dhcpcd will sill 
periodically ask for a DHCP lease. The timings of this are from RFC2131, 
but essentially we send one request every few seconds and then more 
slowly, upto a minute between messages.
5. No

Taking this into account, it seems that your dhcpcd is not listening 
correctly to link messages or the kernel driver is not correctly 
reporting them.
It could very well be a bug in dhcpcd and it's probably best to try a 
newer version. If you need to stick with 5.x for whatever reason, you 
could try and merge the latest code from if-linux.c, link_netlink 
function into your sources.

Thanks

Roy

[1] In dhcpcd-6.x the default timeout is 30 seconds, I think earlier 
versions could have been 1 minute or more. You can adjust this with the 
--timeout <seconds> option.