Date: Mon, 29 Dec 2008 12:33:18 +0100 From: <ajassal.ext@orange-ftgroup.com> To: <freebsd-net@freebsd.org> Cc: khadija.daoud@orange-ftgroup.com Subject: SCTP : problems in sending ASCONF chunks Message-ID: <3418F3471F1CA4409901547349FFAE2E0910679F@ftrdmel2>
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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=3D1 # sysctl -w net.inet.sctp.mobility_fasthandoff=3D1 # sysctl -w net.inet.sctp.debug=3D0x00f301f0 (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 :=20 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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