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Date:      Tue, 3 Jun 2014 17:53:50 -0400
From:      suraj sandhu <surajsandhu.bsd@gmail.com>
To:        freebsd-net@freebsd.org
Subject:   Query regarding net.inet.tcp.nolocaltimewait
Message-ID:  <CAAFvPEFAhq87KbL2OiX=0PHy=_Zo0G1omCLxi6%2BO3b4Owya0dg@mail.gmail.com>
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Hi,

I am using FreeBsd 8.2 and the behavior I am trying to understand is
why there is no final ACK being sent by the client if
net.inet.tcp.nolocaltimewait is set. Due to this server side
communication need to rely upon receiving the RST for clean-up.
Especially in the cases where client port is reused soon after the the
connection being closed, additional resets are triggered.

  198 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L198>;
void
  199 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L199>;
tcp_twstart <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tcp_twstart>(struct
tcpcb <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tcpcb>;
*tp <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tp>)
  200 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L200>;
{
  201 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L201>;
        struct tcptw
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tcptw>;
*tw;
  202 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L202>;
        struct inpcb
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=inpcb>;
*inp <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=inp>;
= tp <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tp>->t_inpcb;
  203 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L203>;
        int acknow;
  204 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L204>;
        struct socket
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=socket>;
*so <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=so>;
  205 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L205>;
  206 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L206>;
        INP_INFO_WLOCK_ASSERT
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=INP_INFO_WLOCK_ASSERT>(&V_tcbinfo
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=V_tcbinfo>);
     */* tcp_tw_2msl_reset(). */*
  207 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L207>;
        INP_WLOCK_ASSERT
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=INP_WLOCK_ASSERT>(inp
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=inp>);
  208 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L208>;
  209 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L209>;
        if (V_nolocaltimewait
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=V_nolocaltimewait>;
&& in_localip <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=in_localip>(inp
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=inp>->inp_faddr
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=inp_faddr>))
{
  210 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L210>;
                tp
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tp>; =
tcp_close <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tcp_close>(tp
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tp>);<====
Closing the connection without sending Final ACK.
  211 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L211>;
                if (tp
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=tp>; !=
NULL <http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=NULL>)
  212 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L212>;
                        INP_WUNLOCK
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=INP_WUNLOCK>(inp
<http://fxr.watson.org/fxr/source/netinet/ident?v=FREEBSD82;i=inp>);
  213 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L213>;
                return;
  214 <http://fxr.watson.org/fxr/source/netinet/source/netinet/tcp_timewait.c?v=FREEBSD82#L214>;
        }

  ...

  ...


I will really appreciate any feedback on it.

-Suraj

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