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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