[Dnsmasq-discuss] Support of labels in --interface

Simon Kelley simon at thekelleys.org.uk
Fri Mar 17 17:30:08 GMT 2017


That seems a good solution. Patch applied, with the man=page changes
re-written and expanded.


Cheers,

Simon.


On 14/03/17 15:11, Petr Menšík wrote:
> Hi,
> 
> I have prepared two patches with suggestion how to fix it.
> 
> Patch 1 warns when a label is used for --interface in default mode.
> Patch 2 corrects manual page about real behavior of --interface with
> labels. Feel free to change it, I am not very good at complicated
> sentences in English.
> 
> I think changing it back again to use all addresses including labels
> would be wrong. Let's just warn user about unexpected results.
> 
> Hope that helps,
> Petr
> 
> Dne 21.2.2017 v 19:50 Simon Kelley napsal(a):
>>> The first problem is, manual page is not updated. It tells you
>>> cannot use labels, but you can. Also it does not tell you you can
>>> use -i eth0,eth0:0,eth0:1,lo, but that is minor change.
>>
>> Documentation point taken.
>>
>>
>>> Labels are now supported and dnsmasq is able to bind only to
>>> secondary IPv4 interface with different address. (Since 2.67!) It
>>> works well with --bind-interfaces. However it has inconsistent
>>> behavior with and without that option.
>>
>>> Let's say my configuration is: 4: virbr0:
>>> <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
>>> group default qlen 1000 link/ether 52:54:00:2b:ee:d3 brd
>>> ff:ff:ff:ff:ff:ff inet 192.168.122.1/24 brd 192.168.122.255 scope
>>> global virbr0 valid_lft forever preferred_lft forever inet
>>> 192.168.122.254/24 scope global secondary virbr0:1 valid_lft
>>> forever preferred_lft forever
>>
>>
>>> $ dnsmasq -i virbr0 will respond to queries to both addresses. It
>>> might be useful backward compatibility feature. However $ dnsmasq
>>> -i virbr0:1 Will respond only on address 192.168.122.254. Ok, call
>>> it a feature.
>>
>>> Problem is, $ dnsmasq -i virbr0 -z Will respond only on address
>>> 192.168.122.1, as I would expect.
>>
>>> $ dnsmasq -i virbr0:1 -z Behaves the same way, as without -z.
>>
>>> I think different behavior is an error. It might be a feature, but
>>> even then, it has to be documented. Opinions?
>>
>> The different behavior is certainly undesirable, and can be fixed.
>> Unfortunately, I can only see how to easily fix it so that the
>> --bind-interfaces case works the same way as the default.
> No, please don't do that. I think current state is the best version we
> can prepare now. Just correct the documentation and warn user if he or
> she tries to use unsupported combination.
>>
>> The problem is that the sockets API tells you the interface that the
>> packet arrived on, and that's what's checked with -i. In your example,
>> queries send to 192.168.122.1 and 192.168.122.254 both arrive at
>> interface virbr0, so there's no easy way to tell them apart, except by
>> looking at the address they were sent to and correlating that with the
>> list of interfaces and their addresses .
>>
>> That requires an up-to-date list of all interfaces, which means, if
>> you're going to behave well in the face of interfaces and addresses
>> coming and going, enumerating the list for every packet received,
>> which will likely kill performance.
>>
>> My feeling is that consistency is good, so I'll certainly make a
>> change, the question is, is the current behaviour of -i <interface
>> name> as encompassing _all_ addresses associated with the interface OK?
>>
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>
>>
>>
>>
>>> [1]
>>> http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=3f2873d42c4d
>> 7e7dba32b6e64a3687d43928bc8e
>>
>>>  Cheers, Petr -- Petr Menšík Software Engineer Red Hat,
>>> http://www.redhat.com/ email: pemensik at redhat.com  PGP: 65C6C973
>>
>>
>>> _______________________________________________ Dnsmasq-discuss
>>> mailing list Dnsmasq-discuss at lists.thekelleys.org.uk 
>>> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
>>
>>
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