<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><style><!--
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:DengXian;
panose-1:2 1 6 0 3 1 1 1 1 1;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:Calibri;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal;
font-family:Calibri;
color:windowtext;}
span.EmailStyle18
{mso-style-type:personal-reply;
font-family:Calibri;
color:windowtext;}
span.msoIns
{mso-style-type:export-only;
mso-style-name:"";
text-decoration:underline;
color:teal;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style></div><div>Hi Jiannan,</div><div><br></div><div><span id="zwchr" data-marker="__DIVIDER__">----- On Mar 27, 2017, at 7:16 AM, Jiannan Ouyang <ouyangj@fb.com> wrote:<br></span></div><div data-marker="__QUOTED_TEXT__"><blockquote style="border-left: 2px solid #1010FF; margin-left: 5px; padding-left: 5px; color: #000; font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;" data-mce-style="border-left: 2px solid #1010FF; margin-left: 5px; padding-left: 5px; color: #000; font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;"><div class="WordSection1"><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;">Hi All,</span></p><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;"> </span></p><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;">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.</span></p><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;"> </span></p><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;">According to <a href="http://lxr.free-electrons.com/source/drivers/net/gtp.c#L937" target="_blank">
http://lxr.free-electrons.com/source/drivers/net/gtp.c#L937</a> and <a href="https://github.com/RoadRunnr/osmo-ggsn/blob/master/libgtnl/src/gtp-genl.c#L73" target="_blank">
https://github.com/RoadRunnr/osmo-ggsn/blob/master/libgtnl/src/gtp-genl.c#L73</a>, the NLM_F_EXCL flag is used to prevent updating an existing tunnel. I’m is wondering what is the reason of preventing updating?</span></p></div></blockquote><div>The correct repository for libgtnl is: http://git.osmocom.org/libgtpnl/, my github tree of osmo-ggsn is outdated and shouldn't be used.</div><blockquote style="border-left: 2px solid #1010FF; margin-left: 5px; padding-left: 5px; color: #000; font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;" data-mce-style="border-left: 2px solid #1010FF; margin-left: 5px; padding-left: 5px; color: #000; font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;"><div class="WordSection1"><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;">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.</span></p></div></blockquote><div>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.</div><div>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.</div><div><br data-mce-bogus="1"></div><div>Adding gtp_update_tunnel to libgtpnl should be simple (but beware of the hash key changes).</div><div><br data-mce-bogus="1"></div><div>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.</div><div>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/398199135a6009dcbd421d7a330a5af2d36dda8d</div><div><br data-mce-bogus="1"></div><div>You are welcome to forward port, fix, test, and submit that to the kernel.</div><div><br data-mce-bogus="1"></div><div>Regards</div><div>Andreas</div><div><br data-mce-bogus="1"></div><blockquote style="border-left: 2px solid #1010FF; margin-left: 5px; padding-left: 5px; color: #000; font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;" data-mce-style="border-left: 2px solid #1010FF; margin-left: 5px; padding-left: 5px; color: #000; font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;"><div class="WordSection1"><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;">Regards,</span></p><p class="MsoNormal"><span style="font-size: 11.0pt;" data-mce-style="font-size: 11.0pt;">-Jiannan</span></p></div><br></blockquote></div></div></body></html>