[ovs-dev] 答复: [PATCH] conntrack: add tcp_in_liberal option in userspace conntrack
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  • [ovs-dev] 答复: [PATCH] conntrack: add tcp_in_liberal option in userspace conntrack
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Commit Message

姜立东 June 3, 2019, 7:21 a.m. UTC
Hi Darrell,

By checking latest patch, we notice it has inconsistent behavior on TCP_RST packet with
kernel tcp_liberal option.
In kernel, TCP_RST packet is only checked for TCP_CONNTRACK_CLOSE state, TCP_RST
packet is dropped if its seq is less than peer acked.
In other cases, TCP_RST packets are processed in  tcp_in_window() as other packets, if
tcp_liberal is enabled, they always are accepted.
Please refer to tcp_packet() and tcp_in_window() in kernel conntrack.

Current implementation may cause TCP_RST packet is marked as INVALID by conntrack
due to old seq info in conntrack in hardware-offloading scenario.
So that we suggest to move conntrack_get_tcp_liberal(ct) up in this check to include
TCP_RST packet as below,


-    if (SEQ_GEQ(src->seqhi, end)

-        /* Last octet inside other's window space */

-        && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))

-        /* Retrans: not more than one window back */

-        && (ackskew >= -MAXACKWINDOW)

-        /* Acking not more than one reassembled fragment backwards */

-        && (ackskew <= (MAXACKWINDOW << sws))

-        /* Acking not more than one window forward */

+    if ((SEQ_GEQ(src->seqhi, end)

+          /* Last octet inside other's window space */

+          && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))

+          /* Retrans: not more than one window back */

+          && ackskew >= -MAXACKWINDOW

+          /* Acking not more than one reassembled fragment backwards */

+          && ackskew <= (MAXACKWINDOW << sws))

+          /* Acking not more than one window forward */

         && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo

-            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo))) {

+             || (orig_seq == src->seqlo + 1)

+             || (orig_seq + 1 == src->seqlo)))

+        || conntrack_get_tcp_liberal(ct)) {




Thanks,
Lidong

发件人: Darrell Ball <dlu998@gmail.com>
发送时间: 2019年6月1日 2:11
收件人: 姜立东 <jianglidong3@jd.com>
抄送: dev@openvswitch.org; 王志克 <wangzhike@jd.com>
主题: Re: [ovs-dev] [PATCH] conntrack: add tcp_in_liberal option in userspace conntrack



On Fri, May 31, 2019 at 9:40 AM Darrell Ball <dlu998@gmail.com<mailto:dlu998@gmail.com>> wrote:


On Fri, May 31, 2019 at 2:42 AM 姜立东 <jianglidong3@jd.com<mailto:jianglidong3@jd.com>> wrote:
Hi Darrell,

Thanks for prompt action.

I think there are 2 main differences in your change,
1. Replace Open_vswitch.other_config by dpctl CLI command.
2. One more case to check tcp_liberal as below.
@@ -333,10 +335,12 @@ tcp_conn_update(struct conntrack *ct, struct conn *conn_,
     } else if ((dst->state < CT_DPIF_TCPS_SYN_SENT
                 || dst->state >= CT_DPIF_TCPS_FIN_WAIT_2
                 || src->state >= CT_DPIF_TCPS_FIN_WAIT_2)
-               && SEQ_GEQ(src->seqhi + MAXACKWINDOW, end)
-               /* Within a window forward of the originating packet */
-               && SEQ_GEQ(seq, src->seqlo - MAXACKWINDOW)) {
-               /* Within a window backward of the originating packet */
+               && ((SEQ_GEQ(src->seqhi + MAXACKWINDOW, end)
+                    /* Within a window forward of the originating packet */
+                    && SEQ_GEQ(seq, src->seqlo - MAXACKWINDOW))
+                    /* Within a window backward of the originating packet */
+                   || (conntrack_get_tcp_liberal(ct)
+                       && (tcp_flags & TCP_RST) == 0)))
For item 1, it is fine for us.
For item 2, we didn’t actually hit into this conditional branch in our application, but considering conntrack is in the middle of this path,
it is reasonable to add this check and leave SEQ validation  to endpoints’ local TCP state machine. So it looks good to us.

Lidong

I just noticed you were referring to the "else if" condition above
This change had been dropped in v2 since it is not needed, here:

https://patchwork.ozlabs.org/patch/1107761/

The change in the 'if' condition check is the main algorithm change; you might want to
compare it to the proposed change that you had sent out.

Thanks Darrell




diff --git a/lib/conntrack-tcp.c b/lib/conntrack-tcp.c

index 397aca1..e95d2f3 100644

--- a/lib/conntrack-tcp.c

+++ b/lib/conntrack-tcp.c

@@ -272,16 +272,18 @@  tcp_conn_update(struct conntrack *ct, struct conn *conn_,



     int ackskew = check_ackskew ? dst->seqlo - ack : 0;

 #define MAXACKWINDOW (0xffff + 1500)    /* 1500 is an arbitrary fudge factor */

-    if (SEQ_GEQ(src->seqhi, end)

-        /* Last octet inside other's window space */

-        && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))

-        /* Retrans: not more than one window back */

-        && (ackskew >= -MAXACKWINDOW)

-        /* Acking not more than one reassembled fragment backwards */

-        && (ackskew <= (MAXACKWINDOW << sws))

-        /* Acking not more than one window forward */

+    if (((SEQ_GEQ(src->seqhi, end)

+          /* Last octet inside other's window space */

+          && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))

+          /* Retrans: not more than one window back */

+          && ackskew >= -MAXACKWINDOW

+          /* Acking not more than one reassembled fragment backwards */

+          && ackskew <= (MAXACKWINDOW << sws))

+         || conntrack_get_tcp_liberal(ct))

+          /* Acking not more than one window forward */

         && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo

-            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo))) {

+             || (orig_seq == src->seqlo + 1)

+             || (orig_seq + 1 == src->seqlo))) {

         /* Require an exact/+1 sequence match on resets when possible */



         /* update max window */





Thanks Lidong

The algorithm I used adheres to the liberal mode definition.

For future reference, another important aspect is test support.

Darrell


BR,
Lidong

发件人: Darrell Ball <dlu998@gmail.com<mailto:dlu998@gmail.com>>
发送时间: 2019年5月30日 14:51
收件人: 姜立东 <jianglidong3@jd.com<mailto:jianglidong3@jd.com>>
抄送: dev@openvswitch.org<mailto:dev@openvswitch.org>; 王志克 <wangzhike@jd.com<mailto:wangzhike@jd.com>>
主题: Re: [ovs-dev] [PATCH] conntrack: add tcp_in_liberal option in userspace conntrack

Hi Lidong/Zhike

I sent an alternative implementation: https://mail.openvswitch.org/pipermail/ovs-dev/2019-May/359364.html

Pls take a look and check if it meets your requirements.

Thanks Darrell

On Fri, May 24, 2019 at 10:11 AM Darrell Ball <dlu998@gmail.com<mailto:dlu998@gmail.com>> wrote:
Thanks for the patch Lidong/Zhike

I took an initial look and will send a response next week.

Darrell

On Tue, May 21, 2019 at 8:53 PM 姜立东 <jianglidong3@jd.com<mailto:jianglidong3@jd.com>> wrote:
From 3ce112684921bca74839e109fda91848aa024a54 Mon Sep 17 00:00:00 2001
From: Jiang Lidong <jianglidong3@jd.com<mailto:jianglidong3@jd.com>>
Date: Wed, 22 May 2019 11:21:34 +0800
Subject: [PATCH] conntrack: add tcp_in_liberal option in userspace conntrack

Adding similar cp_in_liberal option in userspace conntrack as
kernel conntrack does to skip seq check on tcp connection.
It prevents packet is marked as INVALID by stable seq
info in conntrack connection.

This option can help to make traffic survive in hardware
offloading cases, especially when traffic is being moved
back to software path from hardware forwarding engine.

Signed-off-by: Lidong Jiang <jianglidong3@jd.com<mailto:jianglidong3@jd.com>>
Signed-off-by: Zhike Wang <wangzhike@jd.com<mailto:wangzhike@jd.com>>

---
lib/conntrack-private.h | 2 ++
lib/conntrack-tcp.c     | 5 +++--
lib/conntrack.c         | 6 ++++++
lib/conntrack.h         | 4 +++-
lib/dpif-netdev.c       | 6 ++++++
5 files changed, 20 insertions(+), 3 deletions(-)

Comments

Darrell Ball June 3, 2019, 3:52 p.m. UTC | #1
On Mon, Jun 3, 2019 at 12:21 AM 姜立东 <jianglidong3@jd.com> wrote:

> Hi Darrell,
>
>
>
> By checking latest patch, we notice it has inconsistent behavior on
> TCP_RST packet with
>
> kernel tcp_liberal option.
>
> In kernel, TCP_RST packet is only checked for TCP_CONNTRACK_CLOSE state,
>

TCP_CONNTRACK_CLOSE is the 'next state' on receiving RST



> TCP_RST
>
> packet is dropped if its seq is less than peer acked.
>
> In other cases, TCP_RST packets are processed in  tcp_in_window() as
> other packets, if
>
> tcp_liberal is enabled, they always are accepted.
>

On receipt of a RST in any present state, tighter checking is done; this
checking is done
before tcp_in_window
<https://elixir.bootlin.com/linux/v4.9.12/ident/tcp_in_window>() is
executed.



> Please refer to tcp_packet() and tcp_in_window() in kernel conntrack.
>
>
>
> Current implementation may cause TCP_RST packet is marked as INVALID by
> conntrack
>
> due to old seq info in conntrack in hardware-offloading scenario.
>
> So that we suggest to move conntrack_get_tcp_liberal(ct) up in this check
> to include
>
> TCP_RST packet as below,
>

I think the tighter checking for RSTs  I am proposing is generally
consistent, although BSD and
Linux are somewhat different.



>
>
> -    if (SEQ_GEQ(src->seqhi, end)
>
> -        /* Last octet inside other's window space */
>
> -        && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))
>
> -        /* Retrans: not more than one window back */
>
> -        && (ackskew >= -MAXACKWINDOW)
>
> -        /* Acking not more than one reassembled fragment backwards */
>
> -        && (ackskew <= (MAXACKWINDOW << sws))
>
> -        /* Acking not more than one window forward */
>
> +    if ((SEQ_GEQ(src->seqhi, end)
>
> +          /* Last octet inside other's window space */
>
> +          && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))
>
> +          /* Retrans: not more than one window back */
>
> +          && ackskew >= -MAXACKWINDOW
>
> +          /* Acking not more than one reassembled fragment backwards */
>
> +          && ackskew <= (MAXACKWINDOW << sws))
>
> +          /* Acking not more than one window forward */
>
>          && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo
>
> -            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo))) {
>
> +             || (orig_seq == src->seqlo + 1)
>
> +             || (orig_seq + 1 == src->seqlo)))
>
> +        || conntrack_get_tcp_liberal(ct)) {
>
>
>
>
>
>
>
> Thanks,
>
> Lidong
>
>
>
> *发件人:* Darrell Ball <dlu998@gmail.com>
> *发送时间:* 2019年6月1日 2:11
> *收件人:* 姜立东 <jianglidong3@jd.com>
> *抄送:* dev@openvswitch.org; 王志克 <wangzhike@jd.com>
> *主题:* Re: [ovs-dev] [PATCH] conntrack: add tcp_in_liberal option in
> userspace conntrack
>
>
>
>
>
>
>
> On Fri, May 31, 2019 at 9:40 AM Darrell Ball <dlu998@gmail.com> wrote:
>
>
>
>
>
> On Fri, May 31, 2019 at 2:42 AM 姜立东 <jianglidong3@jd.com> wrote:
>
> Hi Darrell,
>
>
>
> Thanks for prompt action.
>
>
>
> I think there are 2 main differences in your change,
>
> 1. Replace Open_vswitch.other_config by dpctl CLI command.
>
> 2. One more case to check tcp_liberal as below.
>
> @@ -333,10 +335,12 @@ tcp_conn_update(struct conntrack *ct, struct conn
> *conn_,
>
>      } else if ((dst->state < CT_DPIF_TCPS_SYN_SENT
>
>                  || dst->state >= CT_DPIF_TCPS_FIN_WAIT_2
>
>                  || src->state >= CT_DPIF_TCPS_FIN_WAIT_2)
>
> -               && SEQ_GEQ(src->seqhi + MAXACKWINDOW, end)
>
> -               /* Within a window forward of the originating packet */
>
> -               && SEQ_GEQ(seq, src->seqlo - MAXACKWINDOW)) {
>
> -               /* Within a window backward of the originating packet */
>
> +               && ((SEQ_GEQ(src->seqhi + MAXACKWINDOW, end)
>
> +                    /* Within a window forward of the originating packet
> */
>
> +                    && SEQ_GEQ(seq, src->seqlo - MAXACKWINDOW))
>
> +                    /* Within a window backward of the originating packet
> */
>
> +                   || (conntrack_get_tcp_liberal(ct)
>
> +                       && (tcp_flags & TCP_RST) == 0)))
>
> For item 1, it is fine for us.
>
> For item 2, we didn’t actually hit into this conditional branch in our
> application, but considering conntrack is in the middle of this path,
>
> it is reasonable to add this check and leave SEQ validation  to endpoints’
> local TCP state machine. So it looks good to us.
>
>
>
> Lidong
>
>
>
> I just noticed you were referring to the "else if" condition above
>
> This change had been dropped in v2 since it is not needed, here:
>
>
>
> https://patchwork.ozlabs.org/patch/1107761/
>
>
>
> The change in the 'if' condition check is the main algorithm change; you
> might want to
>
> compare it to the proposed change that you had sent out.
>
>
>
> Thanks Darrell
>
>
>
>
>
>
>
> *diff --git a/lib/conntrack-tcp.c b/lib/conntrack-tcp.c*
>
> *index 397aca1..e95d2f3 100644*
>
> *--- a/lib/conntrack-tcp.c*
>
> *+++ b/lib/conntrack-tcp.c*
>
> *@@ -272,16 +272,18 @@*  tcp_conn_update(struct conntrack *ct, struct conn *conn_,
>
>       int ackskew = check_ackskew ? dst->seqlo - ack : 0;
>
>  #define MAXACKWINDOW (0xffff + 1500)    /* 1500 is an arbitrary fudge factor */
>
> -    if (SEQ_GEQ(src->seqhi, end)
>
> -        /* Last octet inside other's window space */
>
> -        && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))
>
> -        /* Retrans: not more than one window back */
>
> -        && (ackskew >= -MAXACKWINDOW)
>
> -        /* Acking not more than one reassembled fragment backwards */
>
> -        && (ackskew <= (MAXACKWINDOW << sws))
>
> -        /* Acking not more than one window forward */
>
> +    if (((SEQ_GEQ(src->seqhi, end)
>
> +          /* Last octet inside other's window space */
>
> +          && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))
>
> +          /* Retrans: not more than one window back */
>
> +          && ackskew >= -MAXACKWINDOW
>
> +          /* Acking not more than one reassembled fragment backwards */
>
> +          && ackskew <= (MAXACKWINDOW << sws))
>
> +         || conntrack_get_tcp_liberal(ct))
>
> +          /* Acking not more than one window forward */
>
>          && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo
>
> -            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo))) {
>
> +             || (orig_seq == src->seqlo + 1)
>
> +             || (orig_seq + 1 == src->seqlo))) {
>
>          /* Require an exact/+1 sequence match on resets when possible */
>
>           /* update max window */
>
>
>
>
>
>
>
>
>
>
>
> Thanks Lidong
>
>
>
> The algorithm I used adheres to the liberal mode definition.
>
>
>
> For future reference, another important aspect is test support.
>
>
>
> Darrell
>
>
>
>
>
> BR,
>
> Lidong
>
>
>
> *发件人:* Darrell Ball <dlu998@gmail.com>
> *发送时间:* 2019年5月30日 14:51
> *收件人:* 姜立东 <jianglidong3@jd.com>
> *抄送:* dev@openvswitch.org; 王志克 <wangzhike@jd.com>
> *主题:* Re: [ovs-dev] [PATCH] conntrack: add tcp_in_liberal option in
> userspace conntrack
>
>
>
> Hi Lidong/Zhike
>
>
>
> I sent an alternative implementation:
> https://mail.openvswitch.org/pipermail/ovs-dev/2019-May/359364.html
>
>
>
> Pls take a look and check if it meets your requirements.
>
>
>
> Thanks Darrell
>
>
>
> On Fri, May 24, 2019 at 10:11 AM Darrell Ball <dlu998@gmail.com> wrote:
>
> Thanks for the patch Lidong/Zhike
>
>
>
> I took an initial look and will send a response next week.
>
>
>
> Darrell
>
>
>
> On Tue, May 21, 2019 at 8:53 PM 姜立东 <jianglidong3@jd.com> wrote:
>
> From 3ce112684921bca74839e109fda91848aa024a54 Mon Sep 17 00:00:00 2001
> From: Jiang Lidong <jianglidong3@jd.com>
> Date: Wed, 22 May 2019 11:21:34 +0800
> Subject: [PATCH] conntrack: add tcp_in_liberal option in userspace
> conntrack
>
> Adding similar cp_in_liberal option in userspace conntrack as
> kernel conntrack does to skip seq check on tcp connection.
> It prevents packet is marked as INVALID by stable seq
> info in conntrack connection.
>
> This option can help to make traffic survive in hardware
> offloading cases, especially when traffic is being moved
> back to software path from hardware forwarding engine.
>
> Signed-off-by: Lidong Jiang <jianglidong3@jd.com>
> Signed-off-by: Zhike Wang <wangzhike@jd.com>
>
> ---
> lib/conntrack-private.h | 2 ++
> lib/conntrack-tcp.c     | 5 +++--
> lib/conntrack.c         | 6 ++++++
> lib/conntrack.h         | 4 +++-
> lib/dpif-netdev.c       | 6 ++++++
> 5 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/lib/conntrack-private.h b/lib/conntrack-private.h
> index 51b7d7f..9bc99cd 100644
> --- a/lib/conntrack-private.h
> +++ b/lib/conntrack-private.h
> @@ -172,6 +172,8 @@ struct conntrack {
>      /* Fragmentation handling context. */
>      struct ipf *ipf;
> +
> +    bool tcp_be_liberal;
> };
>  /* Lock acquisition order:
> diff --git a/lib/conntrack-tcp.c b/lib/conntrack-tcp.c
> index 397aca1..61abafb 100644
> --- a/lib/conntrack-tcp.c
> +++ b/lib/conntrack-tcp.c
> @@ -272,7 +272,7 @@ tcp_conn_update(struct conntrack *ct, struct conn
> *conn_,
>      int ackskew = check_ackskew ? dst->seqlo - ack : 0;
> #define MAXACKWINDOW (0xffff + 1500)    /* 1500 is an arbitrary fudge
> factor */
> -    if (SEQ_GEQ(src->seqhi, end)
> +    if ((SEQ_GEQ(src->seqhi, end)
>          /* Last octet inside other's window space */
>          && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))
>          /* Retrans: not more than one window back */
> @@ -281,7 +281,8 @@ tcp_conn_update(struct conntrack *ct, struct conn
> *conn_,
>          && (ackskew <= (MAXACKWINDOW << sws))
>          /* Acking not more than one window forward */
>          && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo
> -            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 ==
> src->seqlo))) {
> +            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 ==
> src->seqlo)))
> +            || (ct->tcp_be_liberal)) {
>          /* Require an exact/+1 sequence match on resets when possible */
>          /* update max window */
> diff --git a/lib/conntrack.c b/lib/conntrack.c
> index 6711f5e..bd92710 100644
> --- a/lib/conntrack.c
> +++ b/lib/conntrack.c
> @@ -2282,6 +2282,12 @@ conntrack_ipf_ctx(struct conntrack *ct)
>      return ct->ipf;
> }
> +void
> +conntrack_set_tcp_be_liberal(struct conntrack *ct, bool enabled)
> +{
> +    ct->tcp_be_liberal = enabled;
> +}
> +
> int
> conntrack_dump_start(struct conntrack *ct, struct conntrack_dump *dump,
>                       const uint16_t *pzone, int *ptot_bkts)
> diff --git a/lib/conntrack.h b/lib/conntrack.h
> index 2012150..b8d799d 100644
> --- a/lib/conntrack.h
> +++ b/lib/conntrack.h
> @@ -119,5 +119,7 @@ int conntrack_set_maxconns(struct conntrack *ct,
> uint32_t maxconns);
> int conntrack_get_maxconns(struct conntrack *ct, uint32_t *maxconns);
> int conntrack_get_nconns(struct conntrack *ct, uint32_t *nconns);
> struct ipf *conntrack_ipf_ctx(struct conntrack *ct);
> -
> +
> +void conntrack_set_tcp_be_liberal(struct conntrack *ct, bool enabled);
> +
> #endif /* conntrack.h */
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 5a6f2ab..ae6a18e 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -3823,6 +3823,12 @@ dpif_netdev_set_config(struct dpif *dpif, const
> struct smap *other_config)
>      uint32_t tx_flush_interval, cur_tx_flush_interval;
>      uint64_t rebalance_intvl;
> +    bool tcp_be_liberal = smap_get_bool(other_config,
> +                                        "conntrack_tcp_be_liberal",
> +                                        false);
> +
> +    conntrack_set_tcp_be_liberal(&dp->conntrack, tcp_be_liberal);
> +
>      tx_flush_interval = smap_get_int(other_config, "tx-flush-interval",
>                                       DEFAULT_TX_FLUSH_INTERVAL);
>      atomic_read_relaxed(&dp->tx_flush_interval, &cur_tx_flush_interval);
> --
> 1.8.3.1
>
> _______________________________________________
> dev mailing list
> dev@openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-dev
>
>

Patch
diff mbox series

diff --git a/lib/conntrack-private.h b/lib/conntrack-private.h
index 51b7d7f..9bc99cd 100644
--- a/lib/conntrack-private.h
+++ b/lib/conntrack-private.h
@@ -172,6 +172,8 @@  struct conntrack {
     /* Fragmentation handling context. */
     struct ipf *ipf;
+
+    bool tcp_be_liberal;
};
 /* Lock acquisition order:
diff --git a/lib/conntrack-tcp.c b/lib/conntrack-tcp.c
index 397aca1..61abafb 100644
--- a/lib/conntrack-tcp.c
+++ b/lib/conntrack-tcp.c
@@ -272,7 +272,7 @@  tcp_conn_update(struct conntrack *ct, struct conn *conn_,
     int ackskew = check_ackskew ? dst->seqlo - ack : 0;
#define MAXACKWINDOW (0xffff + 1500)    /* 1500 is an arbitrary fudge factor */
-    if (SEQ_GEQ(src->seqhi, end)
+    if ((SEQ_GEQ(src->seqhi, end)
         /* Last octet inside other's window space */
         && SEQ_GEQ(seq, src->seqlo - (dst->max_win << dws))
         /* Retrans: not more than one window back */
@@ -281,7 +281,8 @@  tcp_conn_update(struct conntrack *ct, struct conn *conn_,
         && (ackskew <= (MAXACKWINDOW << sws))
         /* Acking not more than one window forward */
         && ((tcp_flags & TCP_RST) == 0 || orig_seq == src->seqlo
-            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo))) {
+            || (orig_seq == src->seqlo + 1) || (orig_seq + 1 == src->seqlo)))
+            || (ct->tcp_be_liberal)) {
         /* Require an exact/+1 sequence match on resets when possible */
         /* update max window */
diff --git a/lib/conntrack.c b/lib/conntrack.c
index 6711f5e..bd92710 100644
--- a/lib/conntrack.c
+++ b/lib/conntrack.c
@@ -2282,6 +2282,12 @@  conntrack_ipf_ctx(struct conntrack *ct)
     return ct->ipf;
}
+void
+conntrack_set_tcp_be_liberal(struct conntrack *ct, bool enabled)
+{
+    ct->tcp_be_liberal = enabled;
+}
+
int
conntrack_dump_start(struct conntrack *ct, struct conntrack_dump *dump,
                      const uint16_t *pzone, int *ptot_bkts)
diff --git a/lib/conntrack.h b/lib/conntrack.h
index 2012150..b8d799d 100644
--- a/lib/conntrack.h
+++ b/lib/conntrack.h
@@ -119,5 +119,7 @@  int conntrack_set_maxconns(struct conntrack *ct, uint32_t maxconns);
int conntrack_get_maxconns(struct conntrack *ct, uint32_t *maxconns);
int conntrack_get_nconns(struct conntrack *ct, uint32_t *nconns);
struct ipf *conntrack_ipf_ctx(struct conntrack *ct);
-
+
+void conntrack_set_tcp_be_liberal(struct conntrack *ct, bool enabled);
+
#endif /* conntrack.h */
diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 5a6f2ab..ae6a18e 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -3823,6 +3823,12 @@  dpif_netdev_set_config(struct dpif *dpif, const struct smap *other_config)
     uint32_t tx_flush_interval, cur_tx_flush_interval;
     uint64_t rebalance_intvl;
+    bool tcp_be_liberal = smap_get_bool(other_config,
+                                        "conntrack_tcp_be_liberal",
+                                        false);
+
+    conntrack_set_tcp_be_liberal(&dp->conntrack, tcp_be_liberal);
+
     tx_flush_interval = smap_get_int(other_config, "tx-flush-interval",
                                      DEFAULT_TX_FLUSH_INTERVAL);
     atomic_read_relaxed(&dp->tx_flush_interval, &cur_tx_flush_interval);
--
1.8.3.1