27 Mar
2017
27 Mar
'17
10:30 a.m.
Hi Jiannan,
----- On Mar 27, 2017, at 7:16 AM, Jiannan Ouyang <ouyangj(a)fb.com> wrote:
Hi All,
In current OAI implementation, we found that there are
cases SPGW is out-of-sync
with MME, because of the delete_session_request is not received by the SPGW
because of some errors, however MME has cleared the state of that session. Then
when the UE re-attaches, a new create_session_request is sent to SPGW; and
because we try to allocate the same IP for the same IMSI (local change), the
SPGW will result out in trying to update an existing GTP tunnel.
According to [
http://lxr.free-electrons.com/source/drivers/net/gtp.c#L937 |
http://lxr.free-electrons.com/source/drivers/net/gtp.c#L937 ] and [
https://github.com/RoadRunnr/osmo-ggsn/blob/master/libgtnl/src/gtp-genl.c#L… |
https://github.com/RoadRunnr/osmo-ggsn/blob/master/libgtnl/src/gtp-genl.c#L… ]
, the NLM_F_EXCL flag is used to prevent updating an existing tunnel. I’m is
wondering what is the reason of preventing updating?
The correct repository for libgtnl is: http://git.osmocom.org/libgtpnl/, my github tree of
osmo-ggsn is outdated and shouldn't be used.
While we are actively investigating sending
delete_session_request properly, as
temporary workaround, I’m thinking to recovery from the out-of-sync problem, we
can allow the new GTP tunnel to overwrite the old one in libgtpnl. Your
suggestions are welcomed. Thanks.
It should be possible to update an existing PDP context as long as you don't change
any of the hash keys. That would be GTP version, GTP socket, ms_addr, and i_tei.
The validation of those values for updating is a bit weak in the kernel. Currently, it
would to possible change any of the hash keys without the hash being updated.
Adding gtp_update_tunnel to libgtpnl should be simple (but beware of the hash key
changes).
A gtp_update_tunnel that supports changing any the hash keys would have to set the
NLM_F_REPLACE flag. That is currently not supported by the kernel implementation and
libgtnl is not setting that flag.
I found an old, untested, and most likely incomplete version of an update pdp
implementation for the kernel in my repository at
https://github.com/RoadRunnr/osmo-ggsn/commit/398199135a6009dcbd421d7a330a5…
You are welcome to forward port, fix, test, and submit that to the kernel.
Regards
Andreas
Regards,
-Jiannan