[OpenWrt-Devel] DHCPv6 flash renumbering patches with HE tunnel breaks

Arjen de Korte arjen+openwrt at de-korte.org
Wed Mar 25 16:49:57 EDT 2015

Citeren Arjen de Korte <arjen+openwrt at de-korte.org>:

> I use an IPv6 tunnel provided by Hurricane Electric to provide IPv6  
> access for my LAN. HE tunnels are configured statically (no DHCPv6 /  
> PD involved) and for the purpose of understanding what ranges are  
> used, assume the following:
>     WAN - 2001:DB8:DEAD:BEEF::/64 (local tunnel endpoint at  
> 2001:DB8:DEAD:BEEF::2)
>     LAN - 2001:DB8:CAFE:BABE::/64 (note this is not a subnet of the  
> WAN, I think this may be important here)
> I use both SLAAC + DHCPv6 on the LAN. Devices with DHCPv6 capability  
> are configured with IPv4+IPv6 addresses in /etc/config/network.

In /etc/config/dhcp of course.

> This has worked flawlessly in Barrier Breaker so far. After  
> migrating to Chaos Calmer, DHCPv6 was essentially broken. Devices  
> that previously were using addresses configured through DHCPv6 are  
> now using SLAAC only.
> Looking in the logs of one of the DHCPv6 clients (a laptop using  
> NetworkManager), I noticed that it was handed out a lease with a  
> preferred lifetime of just one (1) second. Consequently, it would  
> attempt to renew the lease it gets every second, causing  
> intermittent IPv6 availability (if at all) and huge CPU spikes on  
> the router at the times the client connected. Reverting back to the  
> version of odhcpd from Barrier Breaker fixed both these problems and  
> DHCPv6 was useable again.
> Digging into the code, the following commit broke odhcpd in my  
> router (Netgear WNDR4300):
>     dhcpv6: allow flash renumbering in hybrid management mode
> https://github.com/sbyx/odhcpd/commit/a5ebe69d1bc387937bc5448534751123833585fd
> Neither of the following two changes to the same part of this code  
> fixed things:
>     dhcpv6: fix calculation of T1 and T2
> https://github.com/sbyx/odhcpd/commit/b461334ab277b6e8fd1622ab7c8a655363bd3f6c
>     DHCPv6: enable flash-renumbering hack only for /64 prefixes
> https://github.com/sbyx/odhcpd/commit/3b628005e66e90770b2757a4a02c1dee25ccb883
> I'm not quite sure what problem these commits are trying to solve,  
> but it looks to me that the logic behind it is somehow not working  
> for me. For all intents and purposes, the IPv6 addresses I use are  
> static, so I see no reason why it would be necessary to renumber  
> addresses at all.
> Any thoughts?
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