[Dnsmasq-discuss] dropped dhcp6 packet logging revisited

[Gene Czarcinski]

The thread was getting way too long so I have started a new one.

> Simon, now that I have given it some thought, dhcp6_packet() should
> never see any dhcpv6 packets except those which it should see. If it
> does see a packet which it must drop, that implies things are not
> configured properly.
>
> For example, if I specify a network in --dhcp-range which happens to be
> on eth0 and then put eth0 in one of the exclude lists, something is 
> wrong.
>
> If --interface and/or --bind-interfaces were not specified and the
> device name associated dhcpv6 packet does not match the device name
> associated with a --dhcp-range that was specified, this is an error.
>
> It might be appropriate to add my_syslog() warnings when such things 
> occur.
>
> Comments?
>

>
> If I understand you correctly the logging code is there already:
>
> http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob;f=src/rfc3315.c;h=9297d52bbd5d13f63810f67b2114704c7b2e9d11;hb=HEAD#l107 
>

I looked over the code and I believe we are mis-communicating.

What you pointed to is involved with the dhcp6_reply().

In dhcp6.c/dhcp6_packet(), there are a number of tests performed which 
can result in a return way before you get to doing dhcp6_reply().

First, let me assume that there are multiple instances of dnsmasq 
running with each on a separate interface/ip6-subnet.  Also, none of 
these were started with interface= specified so, therefore, 
bind-interfaces is meaningless.

I also assume that a received dhcp6 packet is sent to only one instance 
... in the absence of any other information, this could be any of the 
dnsmasq instances, but it will be only one.

If a packet is passed to one of the dnsmasq instances but should really 
have gone to another instance, then that first instance should return 
before processing (one or more of the tests would determine that the 
packet was not for that instance) and the packet will be 
ignored/dropped.  It is these events I would like to see logged.

Now, such logging could produce many messages to syslog.  If such 
logging is added, then perhaps there should be some special dnsmasq 
parameter that has to be specified.

I am going to add some code to do such logging because it seems I need 
some proof that the problem exists.  I have no idea why, but there 
appears to be reluctance on the part of the libvirt developers to accept 
adding the interface= parameter to dnsmasq.  I believe that, even with 
my limited testing, I have seen the problem occur.

Gene