dhcpcd-discuss

On 10/19/19 1:14 PM, Floris Bos wrote:
> There seems to be a problem in which a network interface is sometimes 
> not get assigned an IPv6 link local address if the network interface 
> goes quickly up -> down -> up again. 


Some more information:


Played a bit with adding a couple more debug logging statements to the code.


The problem seems to be that after the link local address is added, the 
kernel eventually sends you a RTM_NEWADDR event.
Upon receipt of the event you add the IPv6 address to your state->addrs 
list.
After it gets removed the kernel eventually sends a RTM_DELADDR and you 
remove it again from the list.

The problem is that those events arrive delayed, and we are hitting a 
situation in which the RTM_NEWADDR event is not delivered until after 
the address has been deleted. And RTM_DELADDR is even lagging further 
behind.

Since state->addr still has the address in the list, 
ipv6_tryaddlinklocal() thinks there is already a link local address, so 
does no attempt to add one.

==
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: interface added
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: executing 
`/libexec/dhcpcd-run-hooks' PREINIT
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: executing 
`/libexec/dhcpcd-run-hooks' NOCARRIER
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: waiting for carrier
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: carrier acquired
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: executing 
`/libexec/dhcpcd-run-hooks' CARRIER
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: IAID 60:99:b3:1e
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: adding address 
fe80::62c8:16be:6909:4f84
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: pltime infinity, vltime 
infinity
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: delaying IPv6 router 
solicitation for 1.0 seconds
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: delaying IPv4 for 0.9 seconds
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: carrier lost
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: executing 
`/libexec/dhcpcd-run-hooks' NOCARRIER
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: deleting address 
fe80::62c8:16be:6909:4f84
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: cmd 20 addr 
fe80::62c8:16be:6909:4f84 addrflags 192
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: carrier acquired
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: executing 
`/libexec/dhcpcd-run-hooks' CARRIER
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: IAID 60:99:b3:1e
Oct 20 22:44:00 raspberrypi dhcpcd[385]: ipv6_tryaddlinklocal: 
ipv6_iffindaddr() did not return null
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: delaying IPv6 router 
solicitation for 0.9 seconds
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: delaying IPv4 for 0.4 seconds
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: cmd 21 addr 
fe80::62c8:16be:6909:4f84 addrflags 192
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: using ClientID 
01:fa:00:60:99:b3:1e
Oct 20 22:44:00 raspberrypi dhcpcd[385]: usb0: soliciting a DHCP lease
==


Yours sincerely,


Floris Bos