[Dnsmasq-discuss] Cannot get IPv6 RA to occur

John Newlin jnewlin at google.com
Wed Mar 8 00:26:44 GMT 2017


Yes if you're bridging multiple interfaces on the lan side, then you would
assign the address the bridge interface.

On Tue, Mar 7, 2017 at 4:19 PM, Aaron Wood <woody77 at gmail.com> wrote:

> 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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