dhcpcd-discuss

On 21/05/2020 20:22, Jeff wrote:
> The second class is where it appears that a renewal of a lease should succeed 
> (ACK from Comcast), but the lease eventually expires. This class of issues was 
> the subject of this thread. Some evidence can be seen in the logs as "failed to 
> renew DHCP, rebinding", below filtered with `fgrep dhcpcd`. As IPv6 seems to be 
> working, this does not appear to be a transport-related issue. Other symptoms 
> include dhcpcd repeatedly attempting to renew the lease before the timers expire 
> (see earlier in this thread).
>
> May 19 20:24:08 dhcpcd[658]: enp0s0f0: REPLY6 received from 
> fe80::201:5cff:fe65:bc46 # Comcast equipment
> May 19 20:24:08 dhcpcd[658]: enp0s0f0: renew in 3600, rebind in 5760, expire in 
> 7200 seconds
> May 19 21:05:55 dhcpcd[658]: enp0s0f0: failed to renew DHCP, rebinding
> May 19 21:24:08 dhcpcd[658]: enp0s0f0: REPLY6 received from 
> fe80::201:5cff:fe65:bc46
> May 19 21:24:08 dhcpcd[658]: enp0s0f0: renew in 3600, rebind in 5760, expire in 
> 7200 seconds
> May 19 22:22:16 dhcpcd[658]: enp0s0f0: failed to renew DHCP, rebinding
> May 19 22:24:08 dhcpcd[658]: enp0s0f0: REPLY6 received from 
> fe80::201:5cff:fe65:bc46
> May 19 22:24:08 dhcpcd[658]: enp0s0f0: renew in 3600, rebind in 5760, expire in 
> 7200 seconds
> May 19 23:24:08 dhcpcd[658]: enp0s0f0: REPLY6 received from 
> fe80::201:5cff:fe65:bc46
> May 19 23:24:08 dhcpcd[658]: enp0s0f0: renew in 3600, rebind in 5760, expire in 
> 7200 seconds
> May 19 23:38:37 dhcpcd[658]: enp0s0f0: failed to renew DHCP, rebinding

OK, this is the DHCPv4 lease failing to renew, not the DHCPv6 lease.
Oddly enough, this is quite normal for edge level DHCP because the DHCP server 
itself is NOT on the same subnet as your router and RENEW is *always* unicast so 
it's expected to fail.

Sadly, there is no option to disable this that's RFC compliant. Newer dhcpcd 
versions should only log the warning once (unless in debug mode).

DHCPv6 on the other hand is broadcast by default, so a RENEW6 generally works.
The DHCPv6 server admin *can* configure unicast if they so want and could suffer 
the same defect, but then that's just a silly admin.

Roy