[Openvpn-devel,14/21] Add mtu paramter to --fragment and change fragment calculation

Message ID 20211207170211.3275837-15-arne@rfc2549.org
State Superseded
Headers show
Series
  • Big buffer/frame refactoring patch set
Related show

Commit Message

Arne Schwabe Dec. 7, 2021, 5:02 p.m.
Instead relying on the link_mtu_dynamic field and its calculation
in the frame struct, add a new field max_fragment_size and add
a calculation of it similar to mssfix.

Also whenever mssfix value is calculated, we also want to calculate
the values for fragment as both options need to be calculated from
the real overhead.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
---
 Changes.rst                       |   9 +--
 doc/man-sections/link-options.rst |  13 ++--
 src/openvpn/forward.c             |   3 +-
 src/openvpn/fragment.c            |   4 +-
 src/openvpn/init.c                |  23 +++----
 src/openvpn/mss.c                 | 101 +++++++++++++++++++++++++++---
 src/openvpn/mss.h                 |  13 +++-
 src/openvpn/mtu.c                 |  66 +------------------
 src/openvpn/mtu.h                 |  22 +++----
 src/openvpn/options.c             |  12 +++-
 src/openvpn/options.h             |   2 +
 src/openvpn/socket.c              |  11 ----
 src/openvpn/socket.h              |   2 -
 src/openvpn/ssl.c                 |  20 ++----
 14 files changed, 157 insertions(+), 144 deletions(-)

Comments

Frank Lichtenheld Dec. 9, 2021, 1:55 p.m. | #1
> Arne Schwabe <arne@rfc2549.org> hat am 07.12.2021 18:02 geschrieben:
> diff --git a/Changes.rst b/Changes.rst
> index cf6a2f86d..c673196fa 100644
> --- a/Changes.rst
> +++ b/Changes.rst
> @@ -63,10 +63,11 @@ Optional ciphers in ``--data-ciphers``
>      those as optional and only use them if the SSL library supports them.
>  
>  
> -Improved ``--mssfix`` calculation
> -    The ``--mssfix`` option now allows an optional :code:`mtu` parameter to specify
> -    that different overhead for IPv4/IPv6 should taken into account and the resulting
> -    size is specified as the total size of the VPN packets including IP and UDP headers.
> +Improved ``--mssfix`` and ``--fragement`` calculation

Typo, should be "--fragment"

> +    The ``--mssfix`` and ``--fragment`` options now allow an optional :code:`mtu`
> +    parameter to specify that different overhead for IPv4/IPv6 should taken into
> +    account and the resulting size is specified as the total size of the VPN packets
> +    including IP and UDP headers.

Regards,
  Frank

--
Frank Lichtenheld
Frank Lichtenheld Dec. 10, 2021, 4:57 p.m. | #2
> Arne Schwabe <arne@rfc2549.org> hat am 07.12.2021 18:02 geschrieben:
> 
> diff --git a/doc/man-sections/link-options.rst b/doc/man-sections/link-options.rst
> index f41c0c4f1..b71656e0b 100644
> --- a/doc/man-sections/link-options.rst
> +++ b/doc/man-sections/link-options.rst
> @@ -24,13 +24,18 @@ the local and the remote host.
>    from any address, not only the address which was specified in the
>    ``--remote`` option.
>  
> ---fragment max
> +--fragment max [mtu]
>    Enable internal datagram fragmentation so that no UDP datagrams are sent
>    which are larger than ``max`` bytes.
>  
> -  The ``max`` parameter is interpreted in the same way as the
> -  ``--link-mtu`` parameter, i.e. the UDP packet size after encapsulation
> -  overhead has been added in, but not including the UDP header itself.
> +  If the :code:`mtu` parameter is present the ``max`` parameter is
> +  interpreted to include IP and UDP encapsulation overhead. The
> +  :code:`mtu` parameter is introduced in OpenVPN version 2.6.0.
> +
> +  If the :code:`mtu` parameter is absent, the ``max`` parameter is
> +  interpreted in the same way as the ``--link-mtu`` parameter, i.e.
> +  the UDP packet size after encapsulation overhead has been added in,
> +  but not including the UDP header itself.

The same comment as for mssfix applies here: "--fragment max [mtu]" is not valid rst syntax.
Even "--fragment max mtu" is invalid. You need to do something like

--fragment args
  Valid syntaxes::

     fragment max
     fragment max mtu

Like we do for other parameters.

Regards,
--
Frank Lichtenheld

Patch

diff --git a/Changes.rst b/Changes.rst
index cf6a2f86d..c673196fa 100644
--- a/Changes.rst
+++ b/Changes.rst
@@ -63,10 +63,11 @@  Optional ciphers in ``--data-ciphers``
     those as optional and only use them if the SSL library supports them.
 
 
-Improved ``--mssfix`` calculation
-    The ``--mssfix`` option now allows an optional :code:`mtu` parameter to specify
-    that different overhead for IPv4/IPv6 should taken into account and the resulting
-    size is specified as the total size of the VPN packets including IP and UDP headers.
+Improved ``--mssfix`` and ``--fragement`` calculation
+    The ``--mssfix`` and ``--fragment`` options now allow an optional :code:`mtu`
+    parameter to specify that different overhead for IPv4/IPv6 should taken into
+    account and the resulting size is specified as the total size of the VPN packets
+    including IP and UDP headers.
 
 Deprecated features
 -------------------
diff --git a/doc/man-sections/link-options.rst b/doc/man-sections/link-options.rst
index f41c0c4f1..b71656e0b 100644
--- a/doc/man-sections/link-options.rst
+++ b/doc/man-sections/link-options.rst
@@ -24,13 +24,18 @@  the local and the remote host.
   from any address, not only the address which was specified in the
   ``--remote`` option.
 
---fragment max
+--fragment max [mtu]
   Enable internal datagram fragmentation so that no UDP datagrams are sent
   which are larger than ``max`` bytes.
 
-  The ``max`` parameter is interpreted in the same way as the
-  ``--link-mtu`` parameter, i.e. the UDP packet size after encapsulation
-  overhead has been added in, but not including the UDP header itself.
+  If the :code:`mtu` parameter is present the ``max`` parameter is
+  interpreted to include IP and UDP encapsulation overhead. The
+  :code:`mtu` parameter is introduced in OpenVPN version 2.6.0.
+
+  If the :code:`mtu` parameter is absent, the ``max`` parameter is
+  interpreted in the same way as the ``--link-mtu`` parameter, i.e.
+  the UDP packet size after encapsulation overhead has been added in,
+  but not including the UDP header itself.
 
   The ``--fragment`` option only makes sense when you are using the UDP
   protocol (``--proto udp``).
diff --git a/src/openvpn/forward.c b/src/openvpn/forward.c
index 6de6b4d49..3f362e95d 100644
--- a/src/openvpn/forward.c
+++ b/src/openvpn/forward.c
@@ -482,8 +482,7 @@  check_fragment(struct context *c)
     /* OS MTU Hint? */
     if (lsi->mtu_changed && lsi->lsa)
     {
-        frame_adjust_path_mtu(&c->c2.frame_fragment, c->c2.link_socket->mtu,
-                              lsi->lsa->actual.dest.addr.sa.sa_family, lsi->proto);
+        frame_adjust_path_mtu(c);
         lsi->mtu_changed = false;
     }
 
diff --git a/src/openvpn/fragment.c b/src/openvpn/fragment.c
index 6f8fb4476..ce8cd3489 100644
--- a/src/openvpn/fragment.c
+++ b/src/openvpn/fragment.c
@@ -335,12 +335,12 @@  fragment_outgoing(struct fragment_master *f, struct buffer *buf,
             msg(D_FRAG_ERRORS, "FRAG: outgoing buffer is not empty, len=[%d,%d]",
                 buf->len, f->outgoing.len);
         }
-        if (buf->len > PAYLOAD_SIZE_DYNAMIC(frame)) /* should we fragment? */
+        if (buf->len > frame->max_fragment_size) /* should we fragment? */
         {
             /*
              * Send the datagram as a series of 2 or more fragments.
              */
-            f->outgoing_frag_size = optimal_fragment_size(buf->len, PAYLOAD_SIZE_DYNAMIC(frame));
+            f->outgoing_frag_size = optimal_fragment_size(buf->len, frame->max_fragment_size);
             if (buf->len > f->outgoing_frag_size * MAX_FRAGS)
             {
                 FRAG_ERR("too many fragments would be required to send datagram");
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index b3653971c..31ae250bc 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2535,14 +2535,6 @@  frame_finalize_options(struct context *c, const struct options *o)
     frame->buf.payload_size = payload_size;
     frame->buf.headroom = headroom;
     frame->buf.tailroom = tailroom;
-
-    /* Kept to still update/calculate the other fields for now */
-    frame_finalize(frame,
-                   o->ce.link_mtu_defined,
-                   o->ce.link_mtu,
-                   o->ce.tun_mtu_defined,
-                   o->ce.tun_mtu);
-
 }
 
 /*
@@ -3368,8 +3360,8 @@  static void
 do_init_fragment(struct context *c)
 {
     ASSERT(c->options.ce.fragment);
-    frame_set_mtu_dynamic(&c->c2.frame_fragment,
-                          c->options.ce.fragment, SET_MTU_UPPER_BOUND);
+    frame_calculate_dynamic(&c->c2.frame_fragment, &c->c1.ks.key_type,
+                            &c->options, get_link_socket_info(c));
     fragment_frame_init(c->c2.fragment, &c->c2.frame_fragment);
 }
 #endif
@@ -4237,9 +4229,9 @@  init_instance(struct context *c, const struct env_set *env, const unsigned int f
     }
 #endif
 
-    /* initialize dynamic MTU variable */
-    frame_calculate_mssfix(&c->c2.frame, &c->c1.ks.key_type, &c->options,
-                           get_link_socket_info(c));
+    /* initialize dynamic MTU based options (fragment/mssfix) */
+    frame_calculate_dynamic(&c->c2.frame, &c->c1.ks.key_type, &c->options,
+                            get_link_socket_info(c));
 
     /* bind the TCP/UDP socket */
     if (c->mode == CM_P2P || c->mode == CM_TOP || c->mode == CM_CHILD_TCP)
@@ -4291,6 +4283,11 @@  init_instance(struct context *c, const struct env_set *env, const unsigned int f
         link_socket_init_phase2(c);
     }
 
+    /* Update dynamic frame calculation as exact transport socket information
+     * (IP vs IPv6) may be only available after socket phase2 has finished */
+    frame_calculate_dynamic(&c->c2.frame, &c->c1.ks.key_type, &c->options,
+                            get_link_socket_info(c));
+
     /*
      * Actually do UID/GID downgrade, and chroot, if requested.
      * May be delayed by --client, --pull, or --up-delay.
diff --git a/src/openvpn/mss.c b/src/openvpn/mss.c
index b1f10d53e..5b18a8fa2 100644
--- a/src/openvpn/mss.c
+++ b/src/openvpn/mss.c
@@ -33,6 +33,7 @@ 
 #include "crypto.h"
 #include "ssl_common.h"
 #include "memdbg.h"
+#include "forward.h"
 
 /*
  * Lower MSS on TCP SYN packets to fix MTU
@@ -227,16 +228,41 @@  get_ip_encap_overhead(const struct options *options,
     return datagram_overhead(af, lsi->proto);
 }
 
-void
-frame_calculate_mssfix(struct frame *frame, struct key_type *kt,
-                       const struct options *options,
-                       struct link_socket_info *lsi)
+static void
+frame_calculate_fragment(struct frame *frame, struct key_type *kt,
+                         const struct options *options,
+                         struct link_socket_info *lsi)
 {
-    if (options->ce.mssfix == 0)
+#if defined(ENABLE_FRAGMENT)
+    unsigned int payload_size;
+    unsigned int overhead;
+
+    payload_size = frame_calculate_payload_size(frame, options);
+
+    overhead = frame_calculate_protocol_header_size(kt, options, payload_size,
+                                                    false);
+
+    /* The 4 bytes of header that fragment adds itself. The other extra payload
+     * bytes (Ethernet header/compression) are handled by the fragment code
+     * just as part of the payload and therefore automatically taken into
+     * account if the packet needs to fragmented */
+    overhead += 4;
+
+    if (options->ce.fragment_encap)
     {
-        return;
+        overhead += get_ip_encap_overhead(options, lsi);
     }
 
+    /* Calculate the maximum fragment size */
+    frame->max_fragment_size = options->ce.fragment - overhead;
+#endif
+}
+
+static void
+frame_calculate_mssfix(struct frame *frame, struct key_type *kt,
+                       const struct options *options,
+                       struct link_socket_info *lsi)
+{
     unsigned int payload_size;
     unsigned int overhead;
 
@@ -270,4 +296,65 @@  frame_calculate_mssfix(struct frame *frame, struct key_type *kt,
     /* Calculate the maximum MSS value from the max link layer size specified
      * by ce.mssfix */
     frame->mss_fix = options->ce.mssfix - overhead - payload_overhead;
-}
\ No newline at end of file
+}
+
+void
+frame_calculate_dynamic(struct frame *frame, struct key_type *kt,
+                        const struct options *options,
+                        struct link_socket_info *lsi)
+{
+    if (options->ce.fragment > 0)
+    {
+        frame_calculate_fragment(frame, kt, options, lsi);
+    }
+
+    if (options->ce.mssfix > 0)
+    {
+        frame_calculate_mssfix(frame, kt, options, lsi);
+    }
+}
+
+/*
+ * Adjust frame structure based on a Path MTU value given
+ * to us by the OS.
+ */
+void
+frame_adjust_path_mtu(struct context *c)
+{
+    struct link_socket_info *lsi = get_link_socket_info(c);
+    struct options *o = &c->options;
+
+    int pmtu = c->c2.link_socket->mtu;
+    sa_family_t af = lsi->lsa->actual.dest.addr.sa.sa_family;
+    int proto = lsi->proto;
+
+    int encap_overhead = datagram_overhead(af, proto);
+
+    /* check if mssfix and fragment need to be adjusted */
+    if (pmtu < o->ce.mssfix
+        || (o->ce.mssfix_encap && pmtu < o->ce.mssfix + encap_overhead))
+    {
+        const char* mtustr = o->ce.mssfix_encap ? " mtu" : "";
+        msg(D_MTU_INFO, "Note adjusting 'mssfix %d %s' to 'mssfix %d mtu' "
+                        "according to path MTU discovery", o->ce.mssfix,
+            mtustr, pmtu);
+        o->ce.mssfix = pmtu;
+        o->ce.mssfix_encap = true;
+        frame_calculate_dynamic(&c->c2.frame, &c->c1.ks.key_type, o, lsi);
+    }
+
+#if defined(ENABLE_FRAGMENT)
+    if (pmtu < o->ce.fragment ||
+        (o->ce.fragment_encap && pmtu < o->ce.fragment + encap_overhead))
+    {
+        const char* mtustr = o->ce.fragment_encap ? " mtu" : "";
+        msg(D_MTU_INFO, "Note adjusting 'fragment %d %s' to 'fragment %d mtu' "
+                        "according to path MTU discovery", o->ce.mssfix,
+            mtustr, pmtu);
+        o->ce.fragment = pmtu;
+        o->ce.fragment_encap = true;
+        frame_calculate_dynamic(&c->c2.frame_fragment, &c->c1.ks.key_type,
+                                o, lsi);
+    }
+#endif
+}
diff --git a/src/openvpn/mss.h b/src/openvpn/mss.h
index eecc79948..82e0c58f6 100644
--- a/src/openvpn/mss.h
+++ b/src/openvpn/mss.h
@@ -36,8 +36,15 @@  void mss_fixup_ipv6(struct buffer *buf, int maxmss);
 void mss_fixup_dowork(struct buffer *buf, uint16_t maxmss);
 
 /** Set the --mssfix option. */
-void frame_calculate_mssfix(struct frame *frame, struct key_type *kt,
-                            const struct options *options,
-                            struct link_socket_info *lsi);
+void frame_calculate_dynamic(struct frame *frame, struct key_type *kt,
+                             const struct options *options,
+                             struct link_socket_info *lsi);
+
+/**
+ * Checks and adjusts the fragment and mssfix value according to the
+ * discovered path mtu value
+ * @param c     context to adjust
+ */
+void frame_adjust_path_mtu(struct context *c);
 
 #endif
diff --git a/src/openvpn/mtu.c b/src/openvpn/mtu.c
index 88a42a0c5..62a66c8fd 100644
--- a/src/openvpn/mtu.c
+++ b/src/openvpn/mtu.c
@@ -179,68 +179,6 @@  calc_options_string_link_mtu(const struct options *o, const struct frame *frame)
     return payload + overhead;
 }
 
-void
-frame_finalize(struct frame *frame,
-               bool link_mtu_defined,
-               int link_mtu,
-               bool tun_mtu_defined,
-               int tun_mtu)
-{
-    /* Set link_mtu based on command line options */
-    if (tun_mtu_defined)
-    {
-        ASSERT(!link_mtu_defined);
-        frame->link_mtu = tun_mtu + TUN_LINK_DELTA(frame);
-    }
-    else
-    {
-        ASSERT(link_mtu_defined);
-        frame->link_mtu = link_mtu;
-    }
-
-    if (TUN_MTU_SIZE(frame) < TUN_MTU_MIN)
-    {
-        msg(M_WARN, "TUN MTU value (%d) must be at least %d", TUN_MTU_SIZE(frame), TUN_MTU_MIN);
-        frame_print(frame, M_FATAL, "MTU is too small");
-    }
-
-    frame->link_mtu_dynamic = frame->link_mtu;
-}
-
-/*
- * Set the tun MTU dynamically.
- */
-void
-frame_set_mtu_dynamic(struct frame *frame, int mtu, unsigned int flags)
-{
-
-#ifdef ENABLE_DEBUG
-    const int orig_mtu = mtu;
-    const int orig_link_mtu_dynamic = frame->link_mtu_dynamic;
-#endif
-
-    ASSERT(mtu >= 0);
-
-    if (flags & SET_MTU_TUN)
-    {
-        mtu += TUN_LINK_DELTA(frame);
-    }
-
-    if (!(flags & SET_MTU_UPPER_BOUND) || mtu < frame->link_mtu_dynamic)
-    {
-        frame->link_mtu_dynamic = constrain_int(
-            mtu,
-            EXPANDED_SIZE_MIN(frame),
-            EXPANDED_SIZE(frame));
-    }
-
-    dmsg(D_MTU_DEBUG, "MTU DYNAMIC mtu=%d, flags=%u, %d -> %d",
-         orig_mtu,
-         flags,
-         orig_link_mtu_dynamic,
-         frame->link_mtu_dynamic);
-}
-
 /*
  * Move extra_frame octets into extra_tun.  Used by fragmenting code
  * to adjust frame relative to its position in the buffer processing
@@ -266,12 +204,14 @@  frame_print(const struct frame *frame,
     }
     buf_printf(&out, "[");
     buf_printf(&out, " mss_fix:%d", frame->mss_fix);
+#ifdef ENABLE_FRAGMENT
+    buf_printf(&out, " max_frag:%d", frame->max_fragment_size);
+#endif
     buf_printf(&out, " tun_mtu:%d", frame->tun_mtu);
     buf_printf(&out, " headroom:%d", frame->buf.headroom);
     buf_printf(&out, " payload:%d", frame->buf.payload_size);
     buf_printf(&out, " tailroom:%d", frame->buf.tailroom);
     buf_printf(&out, " L:%d", frame->link_mtu);
-    buf_printf(&out, " D:%d", frame->link_mtu_dynamic);
     buf_printf(&out, " EF:%d", frame->extra_frame);
     buf_printf(&out, " EB:%d", frame->extra_buffer);
     buf_printf(&out, " ET:%d", frame->extra_tun);
diff --git a/src/openvpn/mtu.h b/src/openvpn/mtu.h
index ace33a74a..06a00b5bb 100644
--- a/src/openvpn/mtu.h
+++ b/src/openvpn/mtu.h
@@ -113,14 +113,18 @@  struct frame {
     int link_mtu;               /**< Maximum packet size to be sent over
                                  *   the external network interface. */
 
-    unsigned int mss_fix;      /**< The actual MSS value that should be
+    unsigned int mss_fix;       /**< The actual MSS value that should be
                                  *   written to the payload packets. This
                                  *   is the value for IPv4 TCP packets. For
                                  *   IPv6 packets another 20 bytes must
                                  *   be subtracted */
 
-    int link_mtu_dynamic;       /**< Dynamic MTU value for the external
-                                 *   network interface. */
+    int max_fragment_size;      /**< The maximum size of a fragment.
+                                 * Fragmentation is done on the unencrypted
+                                 * payload after (potential) compression. So
+                                 * this value specifies the maximum payload
+                                 * size that can be send in a single fragment
+                                 */
 
     int extra_frame;            /**< Maximum number of bytes that all
                                  *   processing steps together could add.
@@ -195,7 +199,6 @@  struct options;
  * a tap device ifconfiged to an MTU of 1200 might actually want
  * to return a packet size of 1214 on a read().
  */
-#define PAYLOAD_SIZE_DYNAMIC(f)  ((f)->link_mtu_dynamic - (f)->extra_frame)
 #define PAYLOAD_SIZE(f)          ((f)->buf.payload_size)
 
 /*
@@ -203,7 +206,6 @@  struct options;
  * overhead is added.
  */
 #define EXPANDED_SIZE(f)         ((f)->link_mtu)
-#define EXPANDED_SIZE_DYNAMIC(f) ((f)->link_mtu_dynamic)
 #define EXPANDED_SIZE_MIN(f)     (TUN_MTU_MIN + TUN_LINK_DELTA(f))
 
 /*
@@ -224,16 +226,6 @@  struct options;
 
 #define FRAME_HEADROOM(f)          ((f)->buf.headroom)
 
-/*
- * Function prototypes.
- */
-
-void frame_finalize(struct frame *frame,
-                    bool link_mtu_defined,
-                    int link_mtu,
-                    bool tun_mtu_defined,
-                    int tun_mtu);
-
 void frame_subtract_extra(struct frame *frame, const struct frame *src);
 
 void frame_print(const struct frame *frame,
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 8997fa988..e1792d510 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -6115,11 +6115,19 @@  add_option(struct options *options,
         msg(msglevel, "--mtu-dynamic has been replaced by --fragment");
         goto err;
     }
-    else if (streq(p[0], "fragment") && p[1] && !p[2])
+    else if (streq(p[0], "fragment") && p[1] && !p[3])
     {
-/*      VERIFY_PERMISSION (OPT_P_MTU); */
         VERIFY_PERMISSION(OPT_P_MTU|OPT_P_CONNECTION);
         options->ce.fragment = positive_atoi(p[1]);
+
+        if (p[2] && streq(p[2], "mtu"))
+        {
+            options->ce.fragment_encap = true;
+        }
+        else if (p[2])
+        {
+            msg(msglevel, "Unknown parameter to --fragment: %s", p[2]);
+        }
     }
 #endif
     else if (streq(p[0], "mtu-disc") && p[1] && !p[2])
diff --git a/src/openvpn/options.h b/src/openvpn/options.h
index 557edab9b..256318291 100644
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -125,6 +125,8 @@  struct connection_entry
     int mtu_discover_type; /* used if OS supports setting Path MTU discovery options on socket */
 
     int fragment;        /* internal fragmentation size */
+    bool fragment_encap; /* true if --fragment had the "mtu" parameter to
+                          * include overhead from IP and TCP/UDP encapsulation */
     int mssfix;          /* Upper bound on TCP MSS */
     bool mssfix_default; /* true if --mssfix was supplied without a parameter
                           * or 0 was specified as MTU */
diff --git a/src/openvpn/socket.c b/src/openvpn/socket.c
index 93d2e61ec..fe1dfb315 100644
--- a/src/openvpn/socket.c
+++ b/src/openvpn/socket.c
@@ -1644,17 +1644,6 @@  socket_frame_init(const struct frame *frame, struct link_socket *sock)
     }
 }
 
-/*
- * Adjust frame structure based on a Path MTU value given
- * to us by the OS.
- */
-void
-frame_adjust_path_mtu(struct frame *frame, int pmtu, sa_family_t af, int proto)
-{
-    frame_set_mtu_dynamic(frame, pmtu - datagram_overhead(af, proto),
-                          SET_MTU_UPPER_BOUND);
-}
-
 static void
 resolve_bind_local(struct link_socket *sock, const sa_family_t af)
 {
diff --git a/src/openvpn/socket.h b/src/openvpn/socket.h
index 936ef2623..a43ed80b5 100644
--- a/src/openvpn/socket.h
+++ b/src/openvpn/socket.h
@@ -300,8 +300,6 @@  void do_preresolve(struct context *c);
 
 void socket_adjust_frame_parameters(struct frame *frame, int proto);
 
-void frame_adjust_path_mtu(struct frame *frame, int pmtu, sa_family_t af, int proto);
-
 void link_socket_close(struct link_socket *sock);
 
 void sd_close(socket_descriptor_t *sd);
diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c
index c5b085646..79a5660bd 100644
--- a/src/openvpn/ssl.c
+++ b/src/openvpn/ssl.c
@@ -331,7 +331,6 @@  tls_init_control_channel_frame_parameters(const struct frame *data_channel_frame
 
     /* set dynamic link MTU to cap control channel packets at 1250 bytes */
     ASSERT(TUN_LINK_DELTA(frame) < min_int(frame->link_mtu, 1250));
-    frame->link_mtu_dynamic = min_int(frame->link_mtu, 1250) - TUN_LINK_DELTA(frame);
 
     /* calculate the maximum overhead that control channel frames may have */
     int overhead = 0;
@@ -1912,9 +1911,8 @@  tls_session_update_crypto_params_do_work(struct tls_session *session,
     frame_remove_from_extra_frame(frame, crypto_max_overhead());
     crypto_adjust_frame_parameters(frame, &session->opt->key_type,
                                    options->replay, packet_id_long_form);
-    frame_finalize(frame, options->ce.link_mtu_defined, options->ce.link_mtu,
-                   options->ce.tun_mtu_defined, options->ce.tun_mtu);
-    frame_calculate_mssfix(frame, &session->opt->key_type, options, lsi);
+    frame_calculate_dynamic(frame, &session->opt->key_type, options, lsi);
+
     frame_print(frame, D_MTU_INFO, "Data Channel MTU parms");
 
     /*
@@ -1929,7 +1927,7 @@  tls_session_update_crypto_params_do_work(struct tls_session *session,
         frame_remove_from_extra_frame(frame_fragment, crypto_max_overhead());
         crypto_adjust_frame_parameters(frame_fragment, &session->opt->key_type,
                                        options->replay, packet_id_long_form);
-        frame_set_mtu_dynamic(frame_fragment, options->ce.fragment, SET_MTU_UPPER_BOUND);
+        frame_calculate_dynamic(frame_fragment, &session->opt->key_type, options, lsi);
         frame_print(frame_fragment, D_MTU_INFO, "Fragmentation MTU parms");
     }
 
@@ -2982,6 +2980,7 @@  tls_process(struct tls_multi *multi,
             if (buf)
             {
                 int status = key_state_read_ciphertext(&ks->ks_ssl, buf, multi->opt.frame.tun_mtu);
+
                 if (status == -1)
                 {
                     msg(D_TLS_ERRORS,
@@ -3827,17 +3826,6 @@  tls_pre_decrypt_lite(const struct tls_auth_standalone *tas,
         goto error;
     }
 
-    if (buf->len > EXPANDED_SIZE_DYNAMIC(&tas->frame))
-    {
-        dmsg(D_TLS_STATE_ERRORS,
-             "TLS State Error: Large packet (size %d) received from %s -- a packet no larger than %d bytes was expected",
-             buf->len,
-             print_link_socket_actual(from, &gc),
-             EXPANDED_SIZE_DYNAMIC(&tas->frame));
-        goto error;
-    }
-
-
     struct buffer newbuf = clone_buf(buf);
     struct tls_wrap_ctx tls_wrap_tmp = tas->tls_wrap;