[Dnsmasq-discuss] gatway

Simon Kelley simon at thekelleys.org.uk
Tue Oct 8 11:19:37 BST 2013


On 06/10/13 11:32, Vladislav Grishenko wrote:
> Hi, RFC4861 says:
>
>     A router might want to send Router Advertisements without advertising
>     itself as a default router.  For instance, a router might advertise
>     prefixes for stateless address autoconfiguration while not wishing to
>     forward packets.  Such a router sets the Router Lifetime field in
>     outgoing advertisements to zero.
>
>>> is it possible to tell dnsmasq not to announce itself as router?
> So , yes, it's theoretically possible.

That's good information, thanks. In answer to the next question, no, 
it's not possible to configure dnsmasq to send Router Lifetime == 0.

The lifetime, in dhcp-range is used to calculate the lifetimes for 
prefixes, no the router lifetime. In fact the router lifetime is always 
advertised as 1800 seconds, I think.

Since this is a per-broadcast domain thing, and not per prefix thing, it 
needs to be associated with an interface.

Simplest would be

no-router-interface=<interface>[,<interface>,....]

to set the interfaces that get router lifetime of zero.

More complex would be to allow explict setting of the router lifetime 
per interface, that would have to be linked to the RA frequency: you 
wouldn't want a router expiring before it could be re-advertised.


Cheers,

Simon.

>
> Best Regards, Vladislav Grishenko
>
>> -----Original Message-----
>> From: dnsmasq-discuss-bounces at lists.thekelleys.org.uk [mailto:dnsmasq-
>> discuss-bounces at lists.thekelleys.org.uk] On Behalf Of Simon Kelley
>> Sent: Wednesday, October 02, 2013 3:44 PM
>> To: dnsmasq-discuss at lists.thekelleys.org.uk
>> Subject: Re: [Dnsmasq-discuss] gatway
>>
>> On 02/10/13 02:57, Moritz Warning wrote:
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> Hi,
>>>
>>> is it possible to tell dnsmasq not to announce itself as router?
>>> The problem is that connected computers try to use the router as
> gateway.
>>> The router is not the gateway of the network, but some other computer.
>>>
>>> For what it matter, this is the IPv6 setting in my Dnsmasq (version
> 2.66)
>> configuration:
>>>
>>> dhcp-range=public,fdef:1700:bbbb::,ra-names,slaac,64,infinite
>>
>> I don't think it is, except by stopping it from advertising prefixes as
> well, (ie,
>> remove the above line completely). The protocol doesn't
>> (AFAIK) allow prefix advertisements which are not also router
>> advertisements.
>>
>>
>> It _might_ be possible to do the ra-names functionality whilst leaving
>> router/prefix announcement to another host, it would required code
>> changes and I've not thought hard about if it would work or be desirable.
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>>
>>> thanks,
>>> mwarning
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>>> =ign/
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>>>
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