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

Kevin Darbyshire-Bryant kevin at darbyshire-bryant.me.uk
Thu Mar 26 14:56:44 EDT 2015

On 26/03/2015 18:36, Arjen de Korte wrote:
> Citeren Steven Barth <cyrus at openwrt.org>:
>>> In that case, I have a lot of bug reports to file, because none of
>>> the DHCPv6 clients I tried were happy with preferred lifetimes of 1
>>> second on their leases (which includes Windows 7, 8.1 and openSUSE
>>> 13.2).
>> Sorry, I cannot confirm this. I just tried it with both Windows 8.1
>> and Debian testing (w/ network-manager) both didn't react strangely
>> or tried to renew the lease every second. Connectivity was okay.
> The constant refreshes were only with the first patch that introduced
> this behavior (sorry for the confusion), with the current odhcpd
> clients will indeed not attempt to renew continuously. But they won't
> be able to use the address provided by DHCPv6 for outgoing connections
> either. They will use the address from SLAAC most of the time, but at
> the time the lease is renewed, switch to the DHCPv6 address and back
> again to SLAAC 1 second later. Although the window of opportunity for
> this to happen may seem to be small, it is enough for webmail clients
> that happen to check for the source IP to require logging in again
> when this happens (twice in a row actually, as the source IP changes
> twice).
>>>> Besides you also get addresses with higher values for preferred
>>>> lifetime using RAs so you always have usable IPv6 addresses, so if
>>>> your network-manager / OS behaves sanely you shouldn't have any
>>>> issues.
>>> They don't have an issue with IPv6 connectivity, its the source
>>> address that is used *I* have a problem with.
>> Unless you disable RAs there is no way to tell the client which
>> source address to pick anyway. If some OS use the DHCPv6 addresses by
>> default then thats by chance.
> True. But most OSes will pick either one and will stick to that.
> Windows seems to favor DHCPv6, while Linux by defaults selects SLAAC
> then. Both are OK with me. The problem I have with the current
> implementation in odhcpd, is that systems favoring DHCPv6 will switch
> between the two.
>>>> A work-around for this is setting:
>>>> option ra_management 0
>>>> in the lan-section of /etc/config/dhcp which will cause most
>>>> clients to not use DHCPv6 and rely on RAs only.
>>> This is not an option, as the whole purpose of using DHCPv6 for
>>> address configuration is to give clients a fixed IPv6 address. This
>>> has worked correctly since Barrier Breaker was released, I see no
>>> reason why it no longer should.
>> That still works. The client will just not use the address for
>> outgoing traffic.
> This breaks clients that need fixed IPs (in my case, mostly webmail
> clients).
>> I'm fine with making this configurable (current behavior as default)
>> though and would welcome a patch for this. I could put it on my todo
>> but don't really know when I have the time to deal with this.
> I could create a patch for this, but for now I consider this a
> regression, rather than a feature that needs to be configurable. I
> fail to understand the reasons why this change, which deliberately
> breaks the outgoing addresses (even if only momentarily) was introduced.
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I know this isn't ideal and I've come in late to this discussion, have
you considered using the DHCPv6 functionality in dnsmasq?   I have
strenuously avoided radvd & odhcpv6 in preference for keeping everything
in one place.   I shall now return to my cupboard :-)

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