bin/53247: loss of IPv6 address with DHCP in netbsd-8

[Roy%NetBSD.org@localhost,Bixler%NetBSD.org@localhost]

>Number:         53247
>Category:       bin
>Synopsis:       loss of IPv6 address with DHCP in netbsd-8
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue May 01 15:25:00 +0000 2018
>Originator:     rcbixler%nyx.net@localhost
>Release:        netbsd-8
>Organization:
>Environment:
NetBSD rbixler.britannica.net 8.0_RC1 NetBSD 8.0_RC1 (GENERIC) #6: Sun Apr 29 21:28:22 CDT 2018  rcb%rbixler.britannica.net@localhost:/usr/src/sys/arch/amd64/compile/obj/GENERIC amd64
>Description:
After booting up the system with dhcpcd to obtain both IPv4 and IPv6 addresses, I notice after a day or more that I lose the IPv6 address.  I noticed this problem for the first time after I updated to a regular netbsd-8 build from nyftp.netbsd.org from "NetBSD 8.0_BETA (GENERIC.201804122330Z)".  I installed it the next day, the 13th and it ran a few days without incident.  Then I saw the following message in /var/log/messages:

Apr 18 08:33:35 rbixler dhcpcd[284]: ipv6nd_handledata: No buffer space available

30 minutes later, all of my IPv6 routes expired:

Apr 18 09:03:35 rbixler dhcpcd[284]: re0: fe80::ec4:7aff:feda:2df3: router expired
Apr 18 09:03:35 rbixler dhcpcd[284]: re0: fe80::ec4:7aff:feda:2d5b: router expired
Apr 18 09:03:35 rbixler dhcpcd[284]: re0: fe80::ec4:7aff:feda:2e47: router expired

and I lost my IPv6 address:

Apr 18 09:03:35 rbixler dhcpcd[284]: re0: expired address 2620:105:c000:3:e8a3:dd9a:4e6b:10a2/64
Apr 18 09:03:35 rbixler dhcpcd[284]: re0: deleting route to 2620:105:c000:3::/64
Apr 18 09:03:35 rbixler dhcpcd[284]: re0: deleting default route via fe80::ec4:7aff:feda:2df3
Apr 18 09:03:35 rbixler dhcpcd[284]: re0: dropping DHCPv6 due to no valid routers

The problem is reproduceable.  I have also tried to use dhcpcd in IPv4-only mode and get my IPv6 address with plain autoconfiguration and, in that case, it is stable.  I hadn't seen this problem until after the update on the 13th.  I updated the system about a week earlier and didn't see the problem then.  I have updated to NetBSD-8_RC1 since the 13th and the problem persists.

>How-To-Repeat:
Boot the system using dhcpcd to obtain IPv6 address and, after a few days, I lose all IPv6 routes and the IPv6 address.

>Fix:
Downgrading to netbsd-8 as of April 6th or so would fix it.

IPv6 autoconfiguration or static configuration also work.