SCTP : problems in sending ASCONF chunks

Mon Dec 29 15:48:40 UTC 2008

Hi Aman,

I'm not that familiar with the Linux box configuration. If you
look at the INIT/INIT-ACK exchange, does the Linux box support
ASCONF and the SCTP-AUTH extension? Both are required...

Best regards
Michael
On Dec 29, 2008, at 2:36 PM, <ajassal.ext at orange-ftgroup.com> <ajassal.ext at orange-ftgroup.com 
 > wrote:

>
> Hello M.Tüxen,
>
> No, only the PC is running under FreeBSD 7.0. T is running under  
> Linux (kernel version is 2.6.21 and the distribution used is Fedora  
> Core 7). SCTP is running on T thanks to the lksctp implementation,  
> we loaded the sctp module on it and made the necessary  
> configurations so that it is loaded at boot time.
>
> Also, I enable net.sctp.addip_enable=1 on T, just in case, I'm not  
> exactly sure if it has an effect on my tests.
>
> Kind regards
>
>
> Aman Jassal
>
> -----Message d'origine-----
> De : Michael Tüxen [mailto:Michael.Tuexen at lurchi.franken.de]
> Envoyé : lundi 29 décembre 2008 14:09
> À : zze-Abac JASSAL A ext RD-RESA-ISS
> Cc : freebsd-net at freebsd.org; DAOUD TRIKI Khadija RD-RESA-ISS
> Objet : Re: SCTP : problems in sending ASCONF chunks
>
> Hi,
>
> are both machines (T and you PC) running FreeBSD?
>
> Best regards
> Michael
>
> On Dec 29, 2008, at 12:33 PM, <ajassal.ext at orange-ftgroup.com> <ajassal.ext at orange-ftgroup.com 
>   > wrote:
>
>> Hi all,
>>
>> I have been working with SCTP and more specifically with the mobility
>> features of SCTP at my work. Basically, I have been trying to use  
>> SCTP
>> to perform handover tests between 2 separate Wifi networks. I use  
>> IPv6
>> for all my tests.
>>
>> I have a local LAN (wired-network), on which I have 3 machines, one  
>> of
>> them is the machine I use to communicate with for the tests (I'll  
>> call
>> it T to make things simple), and the other two are used as Wifi  
>> Access
>> Points (say Wifi1 and Wifi2 respectively). Since I work with IPv6, I
>> set up both Access Points to send Router Advertisement messages
>> periodically (minimum of 3 seconds, maximum of 4 seconds). That way I
>> can have automatic address reconfiguration when I connect to either  
>> of
>> the access points.
>>
>> The aim of my tests is to use a PC, connect to Wifi1 (for example),
>> launch an SCTP association with T (T sends data to my PC), and then
>> perform a handover on Wifi2. I do make address reconfiguration during
>> the handover process. The important point is that I work with only  
>> ONE
>> address on my network interface. Before I start my tests, I set the
>> following sysctl parameters :
>>
>> # sysctl -w net.inet.sctp.mobility_base=1 # sysctl -w
>> net.inet.sctp.mobility_fasthandoff=1
>> # sysctl -w net.inet.sctp.debug=0x00f301f0		(that is to dump
>> messages in /var/log/messages)
>>
>> net.inet.sctp.auto_asconf is set to 1 by default.
>>
>> I use FreeBSD 7.0 on my PC, I don't know if that is extremely useful
>> but I'm trying to be thorough. This is the script I use to perform
>> handover
>> :
>>
>> ifconfig rum0 inet6 <my old address> delete ifconfig rum0 ssid <the
>> target access point> route del -inet6 default <my old gateway> rtsol
>> rum0
>>
>> If I'm not mistaken, the PC should have sent an ASCONF chunk to
>> perform dynamic address reconfiguration. However what I observed is
>> that nothing happens. No ASCONF chunks are sent, and therefore, T
>> doesn't ever know that it should send data on the PC's newly acquired
>> address.
>>
>> I tried to investigate the problem myself, by adding some debug logs
>> in the sctp source code (to see which functions are called during the
>> handover process), and it seems as if the kernel doesn't ever add an
>> ASCONF chunk to send in its queue... But that's just my understanding
>> of the problem...
>>
>> I looked up in the CVS repository for answers, and to see the various
>> changes that were gradually brought on the code. There, I noticed  
>> that
>> on the revision dating 24th July 2007, changes were made for dynamic
>> address reconfiguration : "Change behaviour so that when the last
>> address is deleted (auto-asconf on a boudall endpoint) no action is
>> taken until an address is added ; at that time an ASCONF add+delete  
>> is
>> sent (if the asoc is still up)"
>>
>> In my humble opinion, this is exactly the case that corresponds to my
>> handover scenario. But I just haven't been able to successfully
>> perform it because I don't seem to send any ASCONF chunk. I'm
>> struggling to understand why I do not see any ASCONF chunk sent.
>>
>> If it can help, I'm also attaching links to the kind of debug logs I
>> got when performing a handover test. This is the kind of debug logs
>> that I got :
>>
>> http://www.divshare.com/download/6200509-560
>>
>> This is another debug logfile, but with my own debug logs added in  
>> the
>> sctp source code :
>>
>> http://www.divshare.com/download/6200504-2e9
>>
>>
>> Many thanks for your work, and I hope someone will be able to help  
>> and
>> shed some light on this problem :-)
>>
>>
>> Aman Jassal
>>
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