Re: Does FreeBSD stack support multiple IP addresses?

[Grant Edwards <grant dot b dot edwards at gmail dot com>]

On 2016-02-23, Lambrecht JÃrgen <J.Lambrecht@TELEVIC.com> wrote:
> On 02/22/2016 04:05 PM, Grant Edwards wrote:

>> When I tried it, the SIOCAIFADDR ioctl() let me set both address and
>> netmask in a single call.  The "case SIOCAIFADDR" code falls through
>> into SIOCSIFNETMASK code.  That didn't work for you?
>
> Indeed, I remember now that I saw that in the code, but then you have 
> the netmask according to the class A/B/C rules, and that is not what we 
> want.
>
>>> - It is only possible to assign a class A/B/C netmask. CIDR netmasks are
>>>    not possible.
>> I think that's always been the case for this version of the stack,
>> hasn't it?
> Indeed.

I just re-ran my tests and verified again that I'm able to set the IP
and netmask in a single call to ioctl(SIOCAIFADDR).  In my tests, I
tried:

 Address         Netmask
-----------      --------------
 11.0.0.104      255.0.0.0
 11.0.0.104      255.255.0.0
 11.0.0.104      255.255.255.0
 11.0.0.104      255.240.0.0
 11.0.0.104      240.0.0.0
 192.168.222.104 240.0.0.0
 192.168.222.104 255.0.0.0
 192.168.222.104 255.240.0.0
 192.168.222.104 255.255.0.0
 192.168.222.104 255.255.240.0
 192.168.222.104 255.255.255.0
 192.168.222.104 255.255.255.240

In all cases, subsequent calls to show_network_tables() showed the IP
address and netmask I requested in the ioctl() call and the correct
corresponding broadcast address.

I'm using an eCos snapshot from 2014.

>>>    I fixed current/src/sys/netinet/in.c for it, but I also adapted
>>>    the ioctl to combine setting IP address and netmask in 1 call
>>>    (so I cannot commit it back). Let me know if you want my fix.

The current SIOCAIFADDR code works fine for me.

> I changed a bit the use of the members of the "inet"-something
> struct (in the ioctl call) to also use the netmask struct member
> that is already in it. Because normally, when you call ioctl
> SIOCSIFNETMASK separately, you specify the netmask in the same
> struct member where you put the IP address for the SIOCAIFADDR call.

But the SIOCAIFADDR call as a _separate_ place where you put the
desired netmask, and AFIACT, that works.

> (I did a fast search in the linux code, but I am not used to that,
> so I did not find the "Linux way")
>
>> I'm confused: based on my experiments and examination of the source
>> code, it already works that way.
>>
> Well, it is both.  Indeed, as you say above, "code falls through
> into SIOCSIFNETMASK code",

> but then it sets "the netmask according to the class A/B/C rules",
> so the netmask is _calculated_, not strictly _set_.  I am completely
> sure about this, I read that whole code part.  (And my collegues did
> the experimentation to set a 255.248.0.0 netmask resulting in a
> 255.255.0.0 mask for 172.24.0.0 which is class B)

I don't know what to tell you other than "it works fine for
me". Unless the output from show_network_tables() is wrong...

-- 
Grant Edwards               grant.b.edwards        Yow! Give them RADAR-GUIDED
                                  at               SKEE-BALL LANES and
                              gmail.com            VELVEETA BURRITOS!!


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