SCTP : problems in sending ASCONF chunks

Mon Dec 29 13:36:37 UTC 2008

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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