Strange Error message SIOCGIFCONF Invalid argument

[Glenn Satchell]

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>Date: Fri, 21 Sep 2007 13:24:56 +0200
>From: Richard Smits <R.Smits at tudelft.nl>
>To: dhcp-users at isc.org
>Subject: Re: Strange Error message SIOCGIFCONF Invalid argument
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>Glenn Satchell wrote:
>>> Date: Thu, 20 Sep 2007 12:45:20 +0200
>>> From: "R.Smits" <R.Smits at tudelft.nl>
>>> To: dhcp-users at isc.org
>>> Subject: Strange Error message SIOCGIFCONF Invalid argument
>>>
>>> Hello,
>>>
>>> We have a Solaris 9 box running ISC 3.03
>>>
>>> We have 64 trunked virtual network interfaces. When we try to make
>>> another one, and start the dhcp server, the messages file says :
>>>
>>> ioctl: SIOCGIFCONF: Invalid argument
>>>
>>> The dhcp server exits with this error message. What does this mean ?
>>>
>>> Greetings... Richard Smits
>>> TU-Delft
>> 
>> A quick google with that error message shows that Solaris returns
>> invalid argument if the size of the buffer passed in the ioctl() call
>> is not big enough to hold the data for all the interfaces.
>> 
>> The string SIOCGIFCONF occurs in only one source file,
>> common/discover.c. In this file this string is used several times in
>> the subroutine discover_interfaces(). It starts with a 2048 byte
>> buffer, but if it gets an error it increases the size and tries again.
>> At least this is the way it is supposed to work in 3.0.4 and 3.0.5. I
>> don't have a copy of the 3.0.3 source code handy to see if this
>> behaviour is in that version. I know it was added somewhere along the
>> years.
>> 
>> First step would be to try a newer release to see if the behaviour changes.
>> 
>> Otherwise you could increase the size of the buffer until it works.
>> 
>> regards,
>> -glenn
>> 
>
>Ah ok.... this is a good explanation.
>
>> Otherwise you could increase the size of the buffer until it works.
>
>Ok, but how do you do this ? We will try a newer version, but a quick
>fix would be better :-)

Edit the source and recompile.

In common/discover.c find the discover_interfaces subroutine. There is
a line in the first few lines there that defines the original buffer:

        char buf [2048];

The 204 might be different in the older version. Make that something like

        char buf [4096];

then recompile and re-install.

The other option is not to trunk all the VLANs to the Sun box, but
rather do the multiple VLANs on a router and enable ip-helper (or
equivalent) on that router with only a single VLAN connected to the Sun
box. I suspect this may be harder to do.

regards,
-glenn

>Greetings, and thank you for your help...
>
>Richard
>