[Dnsmasq-discuss] Cannot get IPv6 RA to occur

Aaron Wood woody77 at gmail.com
Wed Mar 8 00:19:16 GMT 2017


John,

Doesn't the prefix need to be assigned to br0, and not to eth0, so that the
constructor and delegations work correctly?

-Aaron

On Tue, Mar 7, 2017 at 3:33 PM, John Knight <John.Knight at belkin.com> wrote:

> Thanks John for the info on the RA interval.
>
>
>
> My main problem however is that dnsmasq is not advertising the RA.  I
> think I don’t understand how the constructor works.  In my case, the WAN
> interface receives the RA from the upstream router.  I then want to use
> this same prefix of the WAN interface and have dnsmasq send to LAN
> interface.  How do I do this?
>
>
>
> If I specify constructor:eth0, it does indeed find the prefix used to
> create IPv6 Global address on WAN interface… but dnsmasq then assumes I
> want to do RA advertisements on eth0!  Which I do not… I want dnsmasq to
> use the same prefix on the LAN interface (br0).  So this seems to be wrong:
>
> enable-ra
>
> dhcp-range=net:br0,::1,::400,constructor:eth0,ra-names,64,12h
>
> ra-param=br0,60
>
>
>
>
>
> And results in the following logged messages:
>
> ar  2 12:10:40 dnsmasq-dhcp[6026]: DHCPv6, IP range ::1 -- ::400, lease
> time 12h, template for eth0
>
> Mar  2 12:10:40 dnsmasq-dhcp[6026]: DHCPv4-derived IPv6 names on
> eth0
>
> Mar  2 12:10:40 dnsmasq-dhcp[6026]: router advertisement on
> eth0
>
> Mar  2 12:10:40 dnsmasq-dhcp[6026]: DHCPv6, IP range 2001:db8:100:5555::1
> -- 2001:db8:100:5555::400, lease time 12h, con
>
> Mar  2 12:10:40 dnsmasq-dhcp[6026]: DHCPv4-derived IPv6 names on
> 2001:db8:100:5555::, constructed for eth0
>
> Mar  2 12:10:40 dnsmasq-dhcp[6026]: router advertisement on
> 2001:db8:100:5555::, constructed for eth0
>
> Mar  2 12:10:40 dnsmasq-dhcp[6026]: IPv6 router advertisement enabled
>
>
>
> If I specify constructor:br0, then it does not find the prefix as there is
> prefix on the LAN interface.  It seems that dnsmasq assumes that there is
> already a prefix applied to the LAN interface.  The question I have then,
> is how does the LAN interface get configured?  The RA is only seen on the
> WAN interface… how is SLACC applied to the br0 interface?  I am trying to
> understand how this is supposed to work.  I presume that once the LAN
> interface is configured and I use the constructor:br0 in my configuration,
> then I am guessing I will start seeing the RA being advertised. Am I right?
>
>
>
> Comments anyone?
>
>
>
> John
>
> *From:* John Newlin [mailto:jnewlin at google.com]
> *Sent:* Tuesday, March 07, 2017 12:37 PM
> *To:* John Knight
> *Cc:* dnsmasq-discuss at lists.thekelleys.org.uk
> *Subject:* Re: [Dnsmasq-discuss] Cannot get IPv6 RA to occur
>
>
>
> I think you need an:
>
> ra-param=${internal_iterface},60
>
>
>
> The 60 is send an RA every 60 seconds.
>
>
>
>
>
>
>
> On Tue, Mar 7, 2017 at 11:57 AM, John Knight <John.Knight at belkin.com>
> wrote:
>
> Hi,
>
>
>
> I am trying to get dnsmasq to send out IPv6 RAs to my LAN interface (br0),
> but can’t seem to get it to work.  I have tried various configurations I
> have found on the internet, but to no avail.
>
>
>
> I am using dnsmasq 2.76.  My router has WAN interface (eth0) that has an
> IPv6 global address that was configured via PD from RAs received from
> upstream router.  I am trying to use dnsmasq to service the LAN clients on
> br0, and to do this I want to enable dnsmasq router advertisements (RA).
>
>
>
> Here is my current attempt at configuration:
>
> dhcp-range=::a,constructor:br0,ra-names,1d
>
> enable-ra
>
>
>
> I have also tried this:
>
> dhcp-range=tag:br0,::1,::FFFF:FFFF:FFFF:FFFF,constructor:br0,ra-names,1h
>
> enable-ra
>
>
>
> And many other variants of the above.
>
>
>
> The dnsmasq.log file shows the following:
>
> DHCPv4-derived IPv6 names on br0
>
> Router advertisement on br0
>
> IPv6 router advertisement enabled
>
>
>
> However, my LAN client attached to br0 does not receive an RA.  It never
> establishes a global IPv6 address.  I have also verified this using
> “tcpdump –I br0 | grep advert”.  I see no advertisements on the br0
> interface.
>
>
>
> This does raise a few questions for me:
>
> 1)      How does dnsmasq learn of the prefix to use for the RA?  I want
> it to use the prefix received on the WAN interface (eth0) for the RA on the
> LAN interface (br0).  It is not clear to me how to configure this.
>
> You have to request this from the upstream dhcpv6 server, it's called
> prefix delegation.
>
>
>
>
>
> 2)      The dnsmasq log file indicates “Router advertisement on br0”.
> Does this mean that it sent out the Router advertisement on br0?  I thought
> so, but alas, I do not see the RA on br0.
>
> 3)      With radvd, there are controls to determine the frequency of
> advertisements.  Are there any controls for dnsmasq?  What is the default
> frequency of RA advertisement?
>
> 4)      I only have the man page for dnsmasq.  Is there a User guide with
> more details on using dnsmasq?
>
> 5)      I am currently using radvd in the router, and I am thinking if I
> can get this to work, I will stop using radvd.  Are there any compelling
> reasons to use dnsmasq RA over radvd?
>
> 6)      What is the preferred/expected syntax for the dhcp-range?  I have
> seen a number of different variations and find it very confusing... even
> the two examples abover have different syntax.  Both seem to be accepted by
> dnsmasq.
>
>
>
> I appreciate your help with this.  I hope to get this to work soon.
>
>
>
> Thanks,
>
>
>
> John Knight
>
> John.knight at belkin.com
>
>
>
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