Hi!
I have observed a problem while doing some tests with dynamic address
reconfiguration. Let me first describe my setup and application.
Setup: I have two hosts, one that acts as a client and another that acts
as a server. The client has two IPv4 addresses (one on wlan, let's call
it X, and another on a 3G p-to-p connection, let's call it Y). There are
two default routes on the client, and the wlan default has a smaller
metric than the 3G default. The server is single homed. All addresses
belong to different subnets.
Both hosts are running the net-next kernel, downloaded from David
Miller's net-next source tree on 12-May-2010). I have also applied two
extra patches found in: (a)
http://www.spinics.net/lists/linux-sctp/msg00881.html and
(b)http://www.spinics.net/lists/linux-sctp/msg00882.html. I have also
enabled SCTP debugging messages.
Application: In my simple application, only the server transmits
messages to the client. The server uses blocking send() and the client
uses blocking recv(). My client application has a simple policy: When IP
address X is removed from the system, a monitoring process reports this
event to my application. When my application receives this event
notification, it takes two consecutive actions. First, it calls
sctp_bindx() to remove IP address X from the association. Immediately
after that, it calls setsockopt(SET_PEER_PRIMARY_ADDR) to change the
peer's (server's) primary destination to address Y. So, when I execute
"sudo dhcpcd -k wlan0" at the client host, the server should eventually
remove address X from its list of destination addresses and then change
its primary (destination) address to Y. When I execute the command "sudo
dhcpcd wlan0", and when the IP address is finally configured, my client
application gets a notification and calls sctpbindx() to first add the
wlan's IP address X to the association and then calls setsockopt() to
change the peer's (server's) primary to address X. In simple words,
whenever both (wlan and 3G) are available at the client, the client
would like to receive packets from wlan.
In the following experiment, I start the association with the client
having both IP addresses (address X is used for the initial handshake)
and then I execute "sudo dhcpcd -k wlan0" and after one minute I execute
"sudo dhcpcd wlan0". Everything is OK after removing wlan's IP address
(which occures after executing "dhcpcd -x". A fast switchover to 3G
interface is achieved. But after the wlan's address is configured again,
SOMETIMES (not always!!), all subsequent packets (SACKS and ASCONFs)
sent from the client to the server are sent from the wlan interface but
with the 3G IP address!! The source address does not correspond to the
wlan interface, and the wireless network router discards these packets,
which consequently never end up to the server. I have to note that the
first ASCONF for adding the new IP address to the association is
correctly sent from the 3G interface using the 3G IP address. It is the
second ASCONF (for setting peer's primary address) and all SACKs that
are sent from wlan with wrong source IP. Also I observe a delay before
these packets appear in the wlan interface.
I have played with rp_filter and accept_source_route options in
/etc/sysctl.conf but I haven't observed any difference. The values that
I used throughout most of my tests were rp_filter = 0 and
accept_source_route = 1.
Any help will be highly appreciated. If you need the kernel log file I
can also send it.
Thanks in advance,
George
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