At the current state, OVN can not handle fragmented traffic for ACLs
in the userspace datapath (DPDK). Just like in the case of LB
(commit 20a96b9), the kernel DP will try to reassemble the fragments
during CT lookup, however userspace won't reassemble them.

This patch allows OVN to handle fragmented traffic by defining a
translation table on southbound that leverages OpenFlow connection
tracking capabilities. When a stateful flow is created on NB, we add
a hint in the flow. This hint will be read in SB and if the
connection tracking is set to be used, SB will use the alternative
translation table that will use the connection tracking information.

This approach should not change the current behavior and it's only
enabled if acl_udp_ct_translation is set:

ovn-nbctl set NB_Global . options:acl_udp_ct_translation=true

Signed-off-by: Erlon R. Cruz <[email protected]>
---
 controller/lflow.c        |  86 +++++++++-
 controller/lflow.h        |   1 +
 include/ovn/expr.h        |   1 +
 lib/expr.c                |  16 +-
 northd/en-global-config.c |   5 +
 northd/lflow-mgr.c        |  50 +++++-
 northd/lflow-mgr.h        |   8 +-
 northd/northd.c           |  50 ++++--
 tests/automake.mk         |   4 +-
 tests/system-ovn.at       | 273 ++++++++++++++++++++++++++++++
 tests/tcp_simple.py       | 338 ++++++++++++++++++++++++++++++++++++++
 tests/udp_client.py       | 113 +++++++++++++
 12 files changed, 925 insertions(+), 20 deletions(-)
 create mode 100755 tests/tcp_simple.py
 create mode 100755 tests/udp_client.py

diff --git a/controller/lflow.c b/controller/lflow.c
index e84fb2486..85b6d61aa 100644
--- a/controller/lflow.c
+++ b/controller/lflow.c
@@ -51,10 +51,73 @@ COVERAGE_DEFINE(consider_logical_flow);
 /* Contains "struct expr_symbol"s for fields supported by OVN lflows. */
 static struct shash symtab;
 
+/* Alternative symbol table for ACL CT translation.
+ * This symbol table is used when processing ACLs that need to match on
+ * fragmented packets. It maps L4 protocol fields to their connection
+ * tracking equivalents, allowing fragments to be matched correctly.
+ *
+ * For example, "udp.dst" is mapped to MFF_CT_TP_DST instead of MFF_UDP_DST,
+ * so that all fragments (not just the first) can be matched based on the
+ * connection tracking state.
+ */
+static struct shash acl_ct_symtab;
+
+void
+ovn_init_acl_ct_symtab(struct shash *acl_symtab)
+{
+    /* Initialize with the standard symbol table. */
+    ovn_init_symtab(acl_symtab);
+
+    /* Remove the original tcp/udp/sctp symbols that we will override.
+     * Must remove subfields first since they reference the parent. */
+    expr_symtab_remove(acl_symtab, "tcp.src");
+    expr_symtab_remove(acl_symtab, "tcp.dst");
+    expr_symtab_remove(acl_symtab, "tcp");
+    expr_symtab_remove(acl_symtab, "udp.src");
+    expr_symtab_remove(acl_symtab, "udp.dst");
+    expr_symtab_remove(acl_symtab, "udp");
+    expr_symtab_remove(acl_symtab, "sctp.src");
+    expr_symtab_remove(acl_symtab, "sctp.dst");
+    expr_symtab_remove(acl_symtab, "sctp");
+
+    /* Add ct_proto field - CT original direction protocol.
+     * This is used in the tcp/udp/sctp predicate expansions below. */
+    expr_symtab_add_field(acl_symtab, "ct_proto", MFF_CT_NW_PROTO,
+                          "ct.trk", false);
+
+    /* Override TCP protocol and port fields to use CT equivalents.
+     * When "tcp" is used as a predicate, it expands to "ct_proto == 6"
+     * instead of "ip.proto == 6". This ensures we match on the CT state
+     * which is available for all fragments. */
+    expr_symtab_add_predicate(acl_symtab, "tcp",
+                              "ct.trk && !ct.inv && ct_proto == 6");
+    expr_symtab_add_field(acl_symtab, "tcp.src", MFF_CT_TP_SRC,
+                          "tcp", false);
+    expr_symtab_add_field(acl_symtab, "tcp.dst", MFF_CT_TP_DST,
+                          "tcp", false);
+
+    /* Override UDP protocol and port fields */
+    expr_symtab_add_predicate(acl_symtab, "udp",
+                              "ct.trk && !ct.inv && ct_proto == 17");
+    expr_symtab_add_field(acl_symtab, "udp.src", MFF_CT_TP_SRC,
+                          "udp", false);
+    expr_symtab_add_field(acl_symtab, "udp.dst", MFF_CT_TP_DST,
+                          "udp", false);
+
+    /* Override SCTP protocol and port fields */
+    expr_symtab_add_predicate(acl_symtab, "sctp",
+                              "ct.trk && !ct.inv && ct_proto == 132");
+    expr_symtab_add_field(acl_symtab, "sctp.src", MFF_CT_TP_SRC,
+                          "sctp", false);
+    expr_symtab_add_field(acl_symtab, "sctp.dst", MFF_CT_TP_DST,
+                          "sctp", false);
+}
+
 void
 lflow_init(void)
 {
     ovn_init_symtab(&symtab);
+    ovn_init_acl_ct_symtab(&acl_ct_symtab);
 }
 
 struct lookup_port_aux {
@@ -984,7 +1047,24 @@ convert_match_to_expr(const struct sbrec_logical_flow 
*lflow,
                      lflow->match);
         return NULL;
     }
-    struct expr *e = expr_parse_string(lex_str_get(&match_s), &symtab,
+
+    /* Check if this logical flow requires ACL CT translation.
+     * If the tags contains "acl_ct_trans"="true", we use the alternative
+     * symbol table that maps L4 fields (tcp/udp/sctp ports) to their CT
+     * equivalents. */
+    const char *ct_trans = smap_get(&lflow->tags, "acl_ct_trans");
+    struct shash *symtab_to_use = (ct_trans && !strcmp(ct_trans, "true")
+                                   ? &acl_ct_symtab : &symtab);
+
+    if (ct_trans && !strcmp(ct_trans, "true")) {
+        VLOG_DBG("ACL CT Translation enabled for logical flow: match='%s' "
+                 "acl_ct_trans='%s' table=%"PRId64" pipeline=%s",
+                 lflow->match, ct_trans,
+                 lflow->table_id,
+                 lflow->pipeline);
+    }
+
+    struct expr *e = expr_parse_string(lex_str_get(&match_s), symtab_to_use,
                                        addr_sets, port_groups, &addr_sets_ref,
                                        &port_groups_ref,
                                        ldp->datapath->tunnel_key,
@@ -1016,7 +1096,7 @@ convert_match_to_expr(const struct sbrec_logical_flow 
*lflow,
             e = expr_combine(EXPR_T_AND, e, *prereqs);
             *prereqs = NULL;
         }
-        e = expr_annotate(e, &symtab, &error);
+        e = expr_annotate(e, symtab_to_use, &error);
     }
     if (error) {
         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
@@ -2045,6 +2125,8 @@ lflow_destroy(void)
 {
     expr_symtab_destroy(&symtab);
     shash_destroy(&symtab);
+    expr_symtab_destroy(&acl_ct_symtab);
+    shash_destroy(&acl_ct_symtab);
 }
 
 bool
diff --git a/controller/lflow.h b/controller/lflow.h
index 30c6dbebd..3e762d49b 100644
--- a/controller/lflow.h
+++ b/controller/lflow.h
@@ -156,6 +156,7 @@ struct lflow_ctx_out {
 };
 
 void lflow_init(void);
+void ovn_init_acl_ct_symtab(struct shash *acl_symtab);
 void lflow_run(struct lflow_ctx_in *, struct lflow_ctx_out *);
 void lflow_handle_cached_flows(struct lflow_cache *,
                                const struct sbrec_logical_flow_table *);
diff --git a/include/ovn/expr.h b/include/ovn/expr.h
index ae5ab1aab..a96c89d1b 100644
--- a/include/ovn/expr.h
+++ b/include/ovn/expr.h
@@ -319,6 +319,7 @@ struct expr_symbol *expr_symtab_add_ovn_field(struct shash 
*symtab,
                                               const char *name,
                                               enum ovn_field_id id);
 void expr_symtab_destroy(struct shash *symtab);
+void expr_symtab_remove(struct shash *symtab, const char *name);
 
 /* Expression type. */
 enum expr_type {
diff --git a/lib/expr.c b/lib/expr.c
index 288e245c6..2071b3a65 100644
--- a/lib/expr.c
+++ b/lib/expr.c
@@ -1818,7 +1818,21 @@ expr_symtab_destroy(struct shash *symtab)
         free(symbol);
     }
 }
-
+
+/* Removes the symbol with 'name' from 'symtab', freeing its memory.
+ * Does nothing if the symbol doesn't exist. */
+void
+expr_symtab_remove(struct shash *symtab, const char *name)
+{
+    struct expr_symbol *symbol = shash_find_and_delete(symtab, name);
+    if (symbol) {
+        free(symbol->name);
+        free(symbol->prereqs);
+        free(symbol->predicate);
+        free(symbol);
+    }
+}
+
 /* Cloning. */
 
 static struct expr *
diff --git a/northd/en-global-config.c b/northd/en-global-config.c
index 2556b2888..d5499a259 100644
--- a/northd/en-global-config.c
+++ b/northd/en-global-config.c
@@ -717,6 +717,11 @@ check_nb_options_out_of_sync(
         return true;
     }
 
+    if (config_out_of_sync(&nb->options, &config_data->nb_options,
+                           "acl_udp_ct_translation", false)) {
+        return true;
+    }
+
     return false;
 }
 
diff --git a/northd/lflow-mgr.c b/northd/lflow-mgr.c
index a942f287b..a302b6c99 100644
--- a/northd/lflow-mgr.c
+++ b/northd/lflow-mgr.c
@@ -184,6 +184,7 @@ struct ovn_lflow {
     struct ovn_dp_group *dpg;    /* Link to unique Sb datapath group. */
     const char *where;
     const char *flow_desc;
+    bool acl_ct_trans;           /* Use CT-based L4 field translation. */
 
     struct uuid sb_uuid;         /* SB DB row uuid, specified by northd. */
     struct ovs_list referenced_by;  /* List of struct lflow_ref_node. */
@@ -700,7 +701,7 @@ lflow_ref_sync_lflows(struct lflow_ref *lflow_ref,
  * then it may corrupt the hmap.  Caller should ensure thread safety
  * for such scenarios.
  */
-void
+struct ovn_lflow *
 lflow_table_add_lflow(struct lflow_table *lflow_table,
                       const struct ovn_datapath *od,
                       const unsigned long *dp_bitmap, size_t dp_bitmap_len,
@@ -771,6 +772,13 @@ lflow_table_add_lflow(struct lflow_table *lflow_table,
     ovn_dp_group_add_with_reference(lflow, od, dp_bitmap, dp_bitmap_len);
 
     lflow_hash_unlock(hash_lock);
+    return lflow;
+}
+
+void
+ovn_lflow_set_acl_ct_trans(struct ovn_lflow *lflow, bool acl_ct_trans)
+{
+    lflow->acl_ct_trans = acl_ct_trans;
 }
 
 struct ovn_dp_group *
@@ -904,6 +912,7 @@ ovn_lflow_init(struct ovn_lflow *lflow, struct ovn_datapath 
*od,
     lflow->stage_hint = stage_hint;
     lflow->ctrl_meter = ctrl_meter;
     lflow->flow_desc = flow_desc;
+    lflow->acl_ct_trans = false;
     lflow->dpg = NULL;
     lflow->where = where;
     lflow->sb_uuid = sbuuid;
@@ -1096,12 +1105,26 @@ sync_lflow_to_sb(struct ovn_lflow *lflow,
         sbrec_logical_flow_set_match(sbflow, lflow->match);
         sbrec_logical_flow_set_actions(sbflow, lflow->actions);
         sbrec_logical_flow_set_flow_desc(sbflow, lflow->flow_desc);
-        if (lflow->io_port) {
+
+        /* Set tags for io_port and/or acl_ct_trans if needed. */
+        if (lflow->io_port || lflow->acl_ct_trans) {
             struct smap tags = SMAP_INITIALIZER(&tags);
-            smap_add(&tags, "in_out_port", lflow->io_port);
+            if (lflow->io_port) {
+                smap_add(&tags, "in_out_port", lflow->io_port);
+            }
+            if (lflow->acl_ct_trans) {
+                smap_add(&tags, "acl_ct_trans", "true");
+            }
             sbrec_logical_flow_set_tags(sbflow, &tags);
             smap_destroy(&tags);
         }
+
+        VLOG_DBG("Creating new logical flow: "
+                 "pipeline=%s table=%d priority=%d match='%s' "
+                 "actions='%s' acl_ct_trans=%d",
+                 pipeline, table, lflow->priority, lflow->match,
+                 lflow->actions, lflow->acl_ct_trans);
+
         sbrec_logical_flow_set_controller_meter(sbflow, lflow->ctrl_meter);
 
         /* Trim the source locator lflow->where, which looks something like
@@ -1167,6 +1190,27 @@ sync_lflow_to_sb(struct ovn_lflow *lflow,
                 }
             }
         }
+
+        /* Update acl_ct_trans marker in tags if needed.
+         * This must be outside ovn_internal_version_changed check because
+         * the option can be enabled/disabled at runtime. */
+        const char *cur_ct_trans = smap_get_def(&sbflow->tags,
+                                                "acl_ct_trans", "");
+        bool cur_has_ct_trans = !strcmp(cur_ct_trans, "true");
+        if (lflow->acl_ct_trans != cur_has_ct_trans) {
+            VLOG_DBG("Updating logical flow: pipeline=%s "
+                     "table=%"PRId64" priority=%"PRId64" match='%s' "
+                     "old_acl_ct_trans=%d new_acl_ct_trans=%d",
+                     sbflow->pipeline, sbflow->table_id, sbflow->priority,
+                     sbflow->match, cur_has_ct_trans, lflow->acl_ct_trans);
+            if (lflow->acl_ct_trans) {
+                sbrec_logical_flow_update_tags_setkey(
+                    sbflow, "acl_ct_trans", "true");
+            } else {
+                sbrec_logical_flow_update_tags_delkey(
+                    sbflow, "acl_ct_trans");
+            }
+        }
     }
 
     if (lflow->od) {
diff --git a/northd/lflow-mgr.h b/northd/lflow-mgr.h
index c1e72d1be..790498b0b 100644
--- a/northd/lflow-mgr.h
+++ b/northd/lflow-mgr.h
@@ -24,6 +24,7 @@
 struct ovsdb_idl_txn;
 struct ovn_datapath;
 struct ovsdb_idl_row;
+struct ovn_lflow;
 
 /* lflow map which stores the logical flows. */
 struct lflow_table {
@@ -77,7 +78,8 @@ bool lflow_ref_sync_lflows(struct lflow_ref *,
                            const struct sbrec_logical_dp_group_table *);
 
 
-void lflow_table_add_lflow(struct lflow_table *, const struct ovn_datapath *,
+struct ovn_lflow *lflow_table_add_lflow(struct lflow_table *,
+                           const struct ovn_datapath *,
                            const unsigned long *dp_bitmap,
                            size_t dp_bitmap_len, enum ovn_stage stage,
                            uint16_t priority, const char *match,
@@ -87,6 +89,10 @@ void lflow_table_add_lflow(struct lflow_table *, const 
struct ovn_datapath *,
                            const char *where, const char *flow_desc,
                            struct lflow_ref *);
 
+/* Set the acl_ct_trans flag on an lflow. When true, ovn-controller will
+ * use a symbol table that maps L4 port fields to CT equivalents. */
+void ovn_lflow_set_acl_ct_trans(struct ovn_lflow *lflow, bool acl_ct_trans);
+
 /* Adds a row with the specified contents to the Logical_Flow table. */
 #define ovn_lflow_add_with_hint__(LFLOW_TABLE, OD, STAGE, PRIORITY, MATCH, \
                                   ACTIONS, IN_OUT_PORT, CTRL_METER, \
diff --git a/northd/northd.c b/northd/northd.c
index 011f449ec..7542eea1a 100644
--- a/northd/northd.c
+++ b/northd/northd.c
@@ -88,6 +88,12 @@ static bool use_common_zone = false;
  * Otherwise, it will avoid using it.  The default is true. */
 static bool use_ct_inv_match = true;
 
+/* If this option is 'true' northd will rewrite stateful ACL rules that match
+ * on L4 port fields (tcp/udp/sctp) to use connection tracking fields to
+ * properly handle IP fragments. By default this option is set to 'false'.
+ */
+static bool acl_udp_ct_translation = false;
+
 /* If this option is 'true' northd will implicitly add a lowest-priority
  * drop rule in the ACL stage of logical switches that have at least one
  * ACL.
@@ -7178,6 +7184,19 @@ consider_acl(struct lflow_table *lflows, const struct 
ovn_datapath *od,
         match_tier_len = match->length;
     }
 
+    /* Check if this ACL needs CT translation for fragment handling.
+     * All stateful ACLs are marked when the option is enabled; the actual
+     * translation only affects L4 port fields in ovn-controller. */
+    bool needs_ct_trans = has_stateful && acl_udp_ct_translation;
+    struct ovn_lflow *lflow;
+
+    VLOG_DBG("consider_acl: ACL %s action=%s - "
+              "stage=%s priority=%"PRId64" match='%s' "
+              "has_stateful=%d needs_ct_trans=%d",
+              acl->name ? acl->name : "(unnamed)", acl->action,
+              ovn_stage_to_str(stage), acl->priority,
+              acl->match, has_stateful, needs_ct_trans);
+
     if (!has_stateful
         || !strcmp(acl->action, "pass")
         || !strcmp(acl->action, "allow-stateless")) {
@@ -7195,6 +7214,7 @@ consider_acl(struct lflow_table *lflows, const struct 
ovn_datapath *od,
 
         ds_put_cstr(actions, "next;");
         ds_put_format(match, "(%s)", acl->match);
+        /* Stateless ACLs don't need CT translation. */
         ovn_lflow_add_with_hint(lflows, od, stage, priority,
                                 ds_cstr(match), ds_cstr(actions),
                                 &acl->header_, lflow_ref);
@@ -7264,9 +7284,10 @@ consider_acl(struct lflow_table *lflows, const struct 
ovn_datapath *od,
                           (uint8_t) acl->network_function_group->id);
         }
         ds_put_cstr(actions, "next;");
-        ovn_lflow_add_with_hint(lflows, od, stage, priority,
-                                ds_cstr(match), ds_cstr(actions),
-                                &acl->header_, lflow_ref);
+        lflow = ovn_lflow_add_with_hint(lflows, od, stage, priority,
+                                        ds_cstr(match), ds_cstr(actions),
+                                        &acl->header_, lflow_ref);
+        ovn_lflow_set_acl_ct_trans(lflow, needs_ct_trans);
 
         /* Match on traffic in the request direction for an established
          * connection tracking entry that has not been marked for
@@ -7295,9 +7316,10 @@ consider_acl(struct lflow_table *lflows, const struct 
ovn_datapath *od,
                           (uint8_t) acl->network_function_group->id);
         }
         ds_put_cstr(actions, "next;");
-        ovn_lflow_add_with_hint(lflows, od, stage, priority,
-                                ds_cstr(match), ds_cstr(actions),
-                                &acl->header_, lflow_ref);
+        lflow = ovn_lflow_add_with_hint(lflows, od, stage, priority,
+                                        ds_cstr(match), ds_cstr(actions),
+                                        &acl->header_, lflow_ref);
+        ovn_lflow_set_acl_ct_trans(lflow, needs_ct_trans);
     } else if (!strcmp(acl->action, "drop")
                || !strcmp(acl->action, "reject")) {
         if (acl->network_function_group) {
@@ -7322,9 +7344,10 @@ consider_acl(struct lflow_table *lflows, const struct 
ovn_datapath *od,
         build_acl_sample_label_action(actions, acl, acl->sample_new, NULL,
                                       obs_stage);
         ds_put_cstr(actions, "next;");
-        ovn_lflow_add_with_hint(lflows, od, stage, priority,
-                                ds_cstr(match), ds_cstr(actions),
-                                &acl->header_, lflow_ref);
+        lflow = ovn_lflow_add_with_hint(lflows, od, stage, priority,
+                                        ds_cstr(match), ds_cstr(actions),
+                                        &acl->header_, lflow_ref);
+        ovn_lflow_set_acl_ct_trans(lflow, needs_ct_trans);
         /* For an existing connection without ct_mark.blocked set, we've
          * encountered a policy change. ACLs previously allowed
          * this connection and we committed the connection tracking
@@ -7349,9 +7372,10 @@ consider_acl(struct lflow_table *lflows, const struct 
ovn_datapath *od,
         ds_put_format(actions,
                       "ct_commit { ct_mark.blocked = 1; "
                       "ct_label.obs_point_id = %"PRIu32"; }; next;", obs_pid);
-        ovn_lflow_add_with_hint(lflows, od, stage, priority,
-                                ds_cstr(match), ds_cstr(actions),
-                                &acl->header_, lflow_ref);
+        lflow = ovn_lflow_add_with_hint(lflows, od, stage, priority,
+                                        ds_cstr(match), ds_cstr(actions),
+                                        &acl->header_, lflow_ref);
+        ovn_lflow_set_acl_ct_trans(lflow, needs_ct_trans);
     }
 }
 
@@ -20273,6 +20297,8 @@ ovnnb_db_run(struct northd_input *input_data,
 
     use_ct_inv_match = smap_get_bool(input_data->nb_options,
                                      "use_ct_inv_match", true);
+    acl_udp_ct_translation = smap_get_bool(input_data->nb_options,
+                                           "acl_udp_ct_translation", false);
 
     /* deprecated, use --event instead */
     controller_event_en = smap_get_bool(input_data->nb_options,
diff --git a/tests/automake.mk b/tests/automake.mk
index 8ae310547..6c4f8f10c 100644
--- a/tests/automake.mk
+++ b/tests/automake.mk
@@ -332,7 +332,9 @@ CHECK_PYFILES = \
        tests/check_acl_log.py \
        tests/scapy-server.py \
        tests/client.py \
-       tests/server.py
+       tests/server.py \
+       tests/udp_client.py \
+       tests/tcp_simple.py
 
 EXTRA_DIST += $(CHECK_PYFILES)
 PYCOV_CLEAN_FILES += $(CHECK_PYFILES:.py=.py,cover) .coverage
diff --git a/tests/system-ovn.at b/tests/system-ovn.at
index 8af7cb058..445d540bc 100644
--- a/tests/system-ovn.at
+++ b/tests/system-ovn.at
@@ -18680,3 +18680,276 @@ OVS_TRAFFIC_VSWITCHD_STOP(["/.*error receiving.*/d
 /.*terminating with signal 15.*/d"])
 AT_CLEANUP
 ])
+
+OVN_FOR_EACH_NORTHD([
+AT_SETUP([ACL dual direction with fragmentation])
+AT_KEYWORDS([ovnacl])
+
+CHECK_CONNTRACK()
+
+ovn_start
+OVS_TRAFFIC_VSWITCHD_START()
+ADD_BR([br-int])
+ADD_BR([br-ext])
+
+# Logical network:
+# 2 logical switches "public" (192.168.1.0/24) and "internal" (172.16.1.0/24)
+# connected to a router lr. internal has a server. client and server are
+# connected through localnet.
+
+check ovs-ofctl add-flow br-ext action=normal
+# Set external-ids in br-int needed for ovn-controller
+check ovs-vsctl \
+        -- set Open_vSwitch . external-ids:system-id=hv1 \
+        -- set Open_vSwitch . 
external-ids:ovn-remote=unix:$ovs_base/ovn-sb/ovn-sb.sock \
+        -- set Open_vSwitch . external-ids:ovn-encap-type=geneve \
+        -- set Open_vSwitch . external-ids:ovn-encap-ip=169.0.0.1 \
+        -- set bridge br-int fail-mode=secure 
other-config:disable-in-band=true \
+        -- set Open_vSwitch . external-ids:ovn-bridge-mappings=phynet:br-ext
+
+
+# Start ovn-controller
+start_daemon ovn-controller
+check sleep 3
+
+# Set the minimal fragment size for userspace DP.
+# Note that this call will fail for system DP as this setting is not supported 
there.
+ovs-appctl dpctl/ipf-set-min-frag v4 500
+
+check ovn-nbctl lr-add lr
+check ovn-nbctl ls-add internal
+check ovn-nbctl ls-add public
+
+check ovn-nbctl lrp-add lr lr-pub 00:00:01:01:02:03 192.168.1.1/24
+check ovn-nbctl lsp-add  public pub-lr -- set Logical_Switch_Port pub-lr \
+    type=router options:router-port=lr-pub addresses=\"00:00:01:01:02:03\"
+
+check ovn-nbctl lrp-add lr lr-internal 00:00:01:01:02:04 172.16.1.1/24
+check ovn-nbctl lsp-add internal internal-lr -- set Logical_Switch_Port 
internal-lr \
+    type=router options:router-port=lr-internal addresses=\"00:00:01:01:02:04\"
+
+check ovn-nbctl lsp-add public ln_port \
+                -- lsp-set-addresses ln_port unknown \
+                -- lsp-set-type ln_port localnet \
+                -- lsp-set-options ln_port network_name=phynet
+
+ADD_NAMESPACES(client)
+ADD_VETH(client, client, br-int, "172.16.1.3/24", "f0:00:00:01:02:03", \
+         "172.16.1.1")
+check ovn-nbctl lsp-add internal client \
+-- lsp-set-addresses client "f0:00:00:01:02:03 172.16.1.3"
+NS_EXEC([client], [ip l set dev client mtu 900])
+NS_EXEC([client], [ip addr add 127.0.0.1/24 dev lo])
+NS_EXEC([client], [ip link set up dev lo])
+NS_EXEC([client], [ip a])
+
+ADD_NAMESPACES(server)
+ADD_VETH(server, server, br-int, "172.16.1.2/24", "f0:00:0f:01:02:03", \
+         "172.16.1.1")
+check ovn-nbctl lsp-add internal server \
+-- lsp-set-addresses server "f0:00:0f:01:02:03 172.16.1.2"
+NS_EXEC([server], [ip addr add 127.0.0.1/24 dev lo])
+NS_EXEC([server], [ip link set up dev lo])
+NS_EXEC([server], [ip a])
+NS_CHECK_EXEC([server], [ip route add 192.168.1.0/24 via 172.16.1.1 dev 
server])
+
+check ovn-nbctl set logical_router lr options:chassis=hv1
+
+dump_ovs_info() {
+    echo ====== ovs_info $1 ======
+    ovs-ofctl show br-int
+    echo && echo
+    echo =======ovn-nbctl show========
+    ovn-nbctl show
+    echo && echo
+    echo ========ACL===========
+    ovn-nbctl list ACL
+    echo ========Logical_Flow===========
+    ovn-sbctl list Logical_Flow
+    echo && echo
+    echo ========lflow-list===========
+    ovn-sbctl lflow-list
+    echo && echo
+    echo ============br-int===========
+    ovs-ofctl dump-flows -O OpenFlow15 br-int
+    echo && echo
+    echo ============br-int===========
+    ovs-ofctl -O OpenFlow15 dump-flows br-int | grep -E 
"ct_tp|ct_state|ct_nw_proto" | head -10
+    echo && echo
+    echo ============br-ext===========
+    ovs-ofctl dump-flows br-ext
+    echo && echo
+
+}
+
+dump_data_plane_flows() {
+    echo ====== dataplane_flows $1 ======
+    echo ============dp flow-table==============
+    ovs-appctl dpctl/dump-flows
+    echo =======================================
+    echo ============dp flow-table -m===========
+    ovs-appctl dpctl/dump-flows -m
+    echo =======================================
+
+    ovs-appctl dpctl/dump-flows -m > flows-m.txt
+    pmd=$(cat flows-m.txt | awk -F ': ' '/flow-dump from pmd/{print$2}')
+    for ufid in $(awk -F ',' '/ufid:/{print$1}' flows-m.txt); do
+        grep ^$ufid flows-m.txt
+        echo ========= ofproto/detrace $1 $ufid =============
+        ovs-appctl ofproto/detrace $ufid pmd=$pmd
+        echo =======================================
+    done
+
+    echo ============conntrack-table============
+    ovs-appctl dpctl/dump-conntrack
+    echo =======================================
+
+}
+
+test_tcp_traffic() {
+    local src_port=${1:-8080}
+    local dst_port=${2:-8080}
+    local payload_bytes=${3:-10000}
+
+    check ovn-nbctl --wait=hv sync
+    check ovs-appctl dpctl/flush-conntrack
+
+    # Start TCP server in background
+    NETNS_DAEMONIZE([server], [tcp_simple.py --mode server --bind-ip 
172.16.1.2 -p $dst_port], [server.pid])
+
+    # Give server time to start
+    sleep 1
+
+    # Collect only inbound TCP packets on client and server sides
+    NETNS_START_TCPDUMP([client], [-U -i client -Q in -nn -e -q tcp], 
[tcpdump-tcp-client])
+    NETNS_START_TCPDUMP([server], [-U -i server -Q in -nn -e -q tcp], 
[tcpdump-tcp-server])
+
+    # Run TCP client test and capture output
+    NS_EXEC([client], [tcp_simple.py --mode client -s 172.16.1.3 -d 172.16.1.2 
-p $dst_port -B $payload_bytes -n 5 -I 0.2 > tcp_client_output.log 2>&1])
+
+    sleep 1
+    dump_data_plane_flows [tcp]
+
+    # Wait for client to complete and check success
+    OVS_WAIT_UNTIL([test -f tcp_client_output.log])
+    OVS_WAIT_UNTIL([grep -q "Client summary:" tcp_client_output.log])
+
+    # Verify client reported success
+    if ! grep -q "success=0" tcp_client_output.log; then
+        echo "TCP client test failed - checking output:"
+        cat tcp_client_output.log
+        AT_FAIL_IF([true])
+    fi
+
+    # Clean up
+    kill $(cat tcpdump-client.pid) $(cat tcpdump-server.pid) $(cat server.pid) 
2>/dev/null || true
+}
+
+test_fragmented_udp_traffic() {
+    local src_port=${1:-5353}
+    local dst_port=${2:-4242}
+
+    check ovn-nbctl --wait=hv sync
+    check ovs-appctl dpctl/flush-conntrack
+
+    NETNS_DAEMONIZE([server], [nc -l -u 172.16.1.2 $dst_port > /dev/null], 
[server.pid])
+    NETNS_DAEMONIZE([client], [nc -l -u 172.16.1.3 $src_port > /dev/null], 
[client.pid])
+
+    # Collect only inbound UDP packets on client and server sides
+    NETNS_START_TCPDUMP([client], \
+      [-U -i client -Q in -nn -e -q udp], [tcpdump-client])
+    NETNS_START_TCPDUMP([server], \
+      [-U -i server -Q in -nn -e -q udp], [tcpdump-server])
+
+    NS_EXEC([client], [udp_client.py -s 172.16.1.3 -d 172.16.1.2 -S $src_port 
-D $dst_port -M 900 -B 1500 -i client -n 4 -I 0.5])
+    NS_EXEC([server], [udp_client.py -s 172.16.1.2 -d 172.16.1.3 -S $dst_port 
-D $src_port -M 900 -B 1500 -i server -n 4 -I 0.5])
+
+    sleep 1
+    dump_data_plane_flows [udp]
+
+    OVS_WAIT_UNTIL([test "$(cat tcpdump-server.tcpdump | wc -l)" = "8"])
+    OVS_WAIT_UNTIL([test "$(cat tcpdump-client.tcpdump | wc -l)" = "8"])
+
+    kill $(cat tcpdump-client.pid) $(cat tcpdump-server.pid) $(cat server.pid) 
$(cat client.pid)
+}
+
+ovn-appctl -t ovn-northd vlog/set debug
+ovn-appctl -t ovn-controller vlog/set debug
+ovn-appctl vlog/set file:dbg
+ovs-appctl vlog/set dpif:dbg ofproto:dbg conntrack:dbg
+
+check ovn-nbctl set NB_Global . options:acl_udp_ct_translation=true
+
+check ovn-nbctl --wait=hv acl-del internal
+
+# Create port group with both client and server to trigger conjunction flows
+client_uuid=$(ovn-nbctl --bare --columns=_uuid find logical_switch_port 
name=client)
+server_uuid=$(ovn-nbctl --bare --columns=_uuid find logical_switch_port 
name=server)
+check ovn-nbctl pg-add internal_vms $client_uuid $server_uuid
+
+# dump_ovs_info
+
+# Use port group in ACL rules to trigger conjunction flow generation
+
+check ovn-nbctl --wait=hv acl-add internal_vms from-lport 1002 "inport == 
@internal_vms && ip4 && ip4.dst == 0.0.0.0/0 && udp" allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms from-lport 1002 "inport == 
@internal_vms && ip4" allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms from-lport 1002 "inport == 
@internal_vms && ip6" allow-related
+
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst == 22" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst == 123" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst == 1666" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst == 9090" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst == 40004" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst == 51204" 
allow-related
+
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.dst >= 3002 && 
tcp.dst <=13002" allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && udp && udp.dst >= 5002 && 
udp.dst <=10010" allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && tcp && tcp.src >= 3002 && 
tcp.src <=13002" allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && udp && udp.src >= 5002 && 
udp.src <=10010" allow-related
+
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && udp && udp.dst == 123" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && udp && udp.dst == 5060" 
allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && udp && udp.dst == 40004" 
allow-related
+
+
+check # Add the drop rule using port group
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && ip4 && ip4.src == 0.0.0.0/0 && icmp4" allow-related
+check ovn-nbctl --wait=hv acl-add internal_vms to-lport 1002 "outport == 
@internal_vms && arp" allow-related
+
+check ovn-nbctl --wait=hv --log --severity=info acl-add internal_vms to-lport 
100 "outport == @internal_vms" drop
+
+AS_BOX([Testing ACL: test_fragmented_udp_traffic])
+dump_ovs_info test_fragmented_udp_traffic
+test_fragmented_udp_traffic 5060 5060
+
+AS_BOX([Testing ACL: test_tcp_traffic])
+dump_ovs_info test_tcp_traffic
+test_tcp_traffic 9090 9090
+
+AS_BOX([Testing ACL: test_fragmented_udp_traffic_inside_range])
+dump_ovs_info test_fragmented_udp_traffic_inside_range
+test_fragmented_udp_traffic 5005 5005
+
+AS_BOX([Testing ACL: test_tcp_traffic_range])
+dump_ovs_info test_tcp_traffic_range
+test_tcp_traffic 3003 3003
+
+# Reset the option back to default
+as ovn-sb
+OVS_APP_EXIT_AND_WAIT([ovsdb-server])
+
+as ovn-nb
+OVS_APP_EXIT_AND_WAIT([ovsdb-server])
+
+as northd
+OVS_APP_EXIT_AND_WAIT([ovn-northd])
+
+as
+OVS_TRAFFIC_VSWITCHD_STOP(["/failed to query port patch-.*/d
+/connection dropped.*/d
+/WARN|netdev@ovs-netdev: execute.*/d
+/dpif|WARN|system@ovs-system: execute.*/d
+"])
+AT_CLEANUP
+])
+
diff --git a/tests/tcp_simple.py b/tests/tcp_simple.py
new file mode 100755
index 000000000..c5bbed08f
--- /dev/null
+++ b/tests/tcp_simple.py
@@ -0,0 +1,338 @@
+#!/usr/bin/env python3
+"""
+Simple TCP client/server for testing network connectivity and data integrity.
+
+This module provides TCP echo server and client functionality for testing
+network connections, data transmission, and MD5 checksum verification.
+"""
+import socket
+import time
+import argparse
+import sys
+import hashlib
+import random
+
+DEFAULT_SRC_IP = "0.0.0.0"
+DEFAULT_DST_IP = "0.0.0.0"
+DEFAULT_PORT = 8080
+
+
+def calculate_md5(data):
+    """Calculate MD5 checksum of data."""
+    if isinstance(data, str):
+        data = data.encode('utf-8')
+    return hashlib.md5(data).hexdigest()
+
+
+def generate_random_bytes(size):
+    """Generate random bytes that are valid UTF-8."""
+    # Generate random printable ASCII characters (32-126) which are valid UTF-8
+    return bytes([random.randint(32, 126) for _ in range(size)])
+
+
+class TCPServer:
+    """Simple TCP echo server using standard sockets."""
+
+    def __init__(self, bind_ip, port):
+        self.bind_ip = bind_ip
+        self.port = port
+        self.running = False
+        self.server_socket = None
+
+    def start(self):
+        """Start the TCP server."""
+        exit_code = 0
+        self.running = True
+        self.server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        self.server_socket.setsockopt(socket.SOL_SOCKET,
+                                      socket.SO_REUSEADDR, 1)
+
+        try:
+            self.server_socket.bind((self.bind_ip, self.port))
+            self.server_socket.listen(5)
+            print(f"TCP Server listening on {self.bind_ip}:{self.port}")
+
+            while self.running:
+                try:
+                    client_socket, client_addr = self.server_socket.accept()
+                    print(f"Connection from {client_addr[0]}:{client_addr[1]}")
+
+                    # Handle client directly (single-threaded)
+                    self._handle_client(client_socket, client_addr)
+
+                except socket.error as e:
+                    if self.running:
+                        print(f"Socket error: {e}")
+
+        except OSError as e:
+            if e.errno == 99:  # Cannot assign requested address
+                print(f"Error: Cannot bind to {self.bind_ip}:{self.port}")
+            elif e.errno == 98:  # Address already in use
+                print(f"Error: Port {self.port} is already in use.")
+            else:
+                print(f"Error binding to {self.bind_ip}:{self.port}: {e}")
+        except KeyboardInterrupt:
+            print("\nServer shutting down...")
+            exit_code = 0
+        except Exception as e:
+            print(f"Unexpected server error: {e}")
+            exit_code = 1
+        finally:
+            self.running = False
+            if self.server_socket:
+                self.server_socket.close()
+        sys.exit(exit_code)
+
+    def _handle_client(self, client_socket, client_addr):
+        """Handle individual client connection."""
+        total_bytes_received = 0
+        try:
+            while self.running:
+                data = client_socket.recv(4096)
+                if not data:
+                    break
+                client_socket.send(data)
+                total_bytes_received += len(data)
+
+            print(f"Total bytes received: {total_bytes_received}")
+        except socket.error as e:
+            print(f"Client {client_addr[0]}:{client_addr[1]} error: {e}")
+        finally:
+            client_socket.close()
+            print(f"Connection closed with {client_addr[0]}:{client_addr[1]}")
+
+
+class TCPClient:
+    """Simple TCP client using standard sockets."""
+
+    def __init__(self, src_ip, dst_ip, dst_port):
+        self.src_ip = src_ip
+        self.dst_ip = dst_ip
+        self.dst_port = dst_port
+
+    def connect_and_send(self, data_len, iterations=1, interval=0.1,
+                         unique_data=False):
+        """Connect to server and send data."""
+        print(f"TCP Client connecting to {self.dst_ip}:{self.dst_port}")
+
+        success_count = 0
+        correct_responses = 0
+
+        # Generate data once if not using unique data per iteration
+        shared_data_bytes = None
+        shared_md5 = None
+        if not unique_data:
+            shared_data_bytes = generate_random_bytes(data_len)
+            shared_md5 = calculate_md5(shared_data_bytes)
+            print(f"Generated shared buffer: {len(shared_data_bytes)} bytes, "
+                  f"MD5: {shared_md5}")
+
+        return_code = 0
+        for i in range(iterations):
+            iteration_result = self._process_iteration(
+                i, data_len, unique_data, shared_data_bytes, shared_md5)
+            if iteration_result['success']:
+                success_count += 1
+                if iteration_result['checksum_match']:
+                    correct_responses += 1
+            else:
+                return_code = 1
+
+            if i < iterations - 1:
+                time.sleep(interval)
+
+        print(f"Client completed: {success_count}/{iterations} "
+              f"successful connections")
+        print(f"MD5 checksum verification: "
+              f"{correct_responses}/{success_count} correct")
+
+        return_code = 0 if (correct_responses ==
+                           success_count and success_count > 0) else 1
+        return return_code
+
+    def _process_iteration(self, iteration_idx, data_len, unique_data,
+                          shared_data_bytes, shared_md5):
+        """Process a single iteration of the client test."""
+        try:
+            # Create socket and connect
+            client_socket = socket.socket(socket.AF_INET,
+                                          socket.SOCK_STREAM)
+
+            # Bind to specific source IP if provided
+            if self.src_ip != "0.0.0.0":
+                client_socket.bind((self.src_ip, 0))
+
+            client_socket.connect((self.dst_ip, self.dst_port))
+            print(f"Iteration {iteration_idx + 1}: Connected to server")
+
+            # Prepare data and calculate MD5 checksum
+            if unique_data:
+                data_bytes = generate_random_bytes(data_len)
+                original_md5 = calculate_md5(data_bytes)
+                print(f"Iteration {iteration_idx + 1}: Generated unique data, "
+                      f"MD5: {original_md5}")
+            else:
+                data_bytes = shared_data_bytes
+                original_md5 = shared_md5
+                print(f"Iteration {iteration_idx + 1}: Using shared buffer, "
+                      f"MD5: {original_md5}")
+
+            client_socket.send(data_bytes)
+            print(f"Iteration {iteration_idx + 1}: Sent {len(data_bytes)} "
+                  f"bytes")
+
+            # Receive echo response
+            response = self._receive_response(client_socket, len(data_bytes))
+            print(f"Iteration {iteration_idx + 1}: Received {len(response)} "
+                  f"bytes")
+
+            # Calculate MD5 of received data
+            received_md5 = calculate_md5(response)
+            print(f"Iteration {iteration_idx + 1}: Received MD5: "
+                  f"{received_md5}")
+
+            # Verify checksum
+            checksum_match = original_md5 == received_md5
+
+            if checksum_match:
+                print(f"Iteration {iteration_idx + 1}: ✓ MD5 checksum "
+                      f"verified correctly")
+            else:
+                print(f"Iteration {iteration_idx + 1}: ✗ MD5 checksum "
+                      f"mismatch!")
+
+            client_socket.close()
+            return {'success': True, 'checksum_match': checksum_match}
+
+        except ConnectionRefusedError:
+            print(f"Iteration {iteration_idx + 1}: Connection refused to "
+                  f"{self.dst_ip}:{self.dst_port}")
+            return {'success': False, 'checksum_match': False}
+        except socket.timeout:
+            print(f"Iteration {iteration_idx + 1}: Connection timeout to "
+                  f"{self.dst_ip}:{self.dst_port}")
+            return {'success': False, 'checksum_match': False}
+        except OSError as os_error:
+            self._handle_os_error(iteration_idx, os_error)
+            return {'success': False, 'checksum_match': False}
+        except socket.error as sock_error:
+            print(f"Iteration {iteration_idx + 1}: Socket error: {sock_error}")
+            return {'success': False, 'checksum_match': False}
+        except Exception as general_error:
+            print(f"Iteration {iteration_idx + 1}: Unexpected error: "
+                  f"{general_error}")
+            return {'success': False, 'checksum_match': False}
+
+    def _receive_response(self, client_socket, bytes_to_receive):
+        """Receive response data from server."""
+        response = b""
+        while len(response) < bytes_to_receive:
+            chunk = client_socket.recv(
+                min(4096, bytes_to_receive - len(response)))
+            if not chunk:
+                break
+            response += chunk
+        return response
+
+    def _handle_os_error(self, iteration_idx, os_error):
+        """Handle OS-specific errors."""
+        if os_error.errno == 99:  # Cannot assign requested address
+            print(f"Iteration {iteration_idx + 1}: Cannot bind to source IP "
+                  f"{self.src_ip}")
+        elif os_error.errno == 101:  # Network is unreachable
+            print(f"Iteration {iteration_idx + 1}: Network unreachable to "
+                  f"{self.dst_ip}:{self.dst_port}")
+        else:
+            print(f"Iteration {iteration_idx + 1}: Network error: {os_error}")
+
+
+def main():
+    """Main function to parse arguments and run TCP client or server."""
+    parser = argparse.ArgumentParser(
+        description="Simple TCP client/server for testing",
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+        epilog="""
+COMMON OPTIONS:
+  --mode {client,server}  Run in client or server mode (required)
+  -p, --port PORT         TCP port (default: 8080)
+
+CLIENT MODE OPTIONS:
+  -s, --src-ip IP         Source IPv4 address (default: 0.0.0.0)
+  -d, --dst-ip IP         Destination IPv4 address (default: 0.0.0.0)
+  -n, --iterations N      Number of connections to make (default: 1)
+  -I, --interval SECS     Seconds between connections (default: 0.1)
+  -B, --payload-bytes N   Total TCP payload bytes (minimum: 500)
+  --unique-data           Generate unique random data for each iteration
+
+SERVER MODE OPTIONS:
+  --bind-ip IP            Server bind IP address (default: 172.16.1.2)
+
+""")
+
+    # Mode selection (required)
+    parser.add_argument("--mode", choices=['client', 'server'], required=True,
+                       help=argparse.SUPPRESS)
+
+    # Common arguments
+    parser.add_argument("-p", "--port", type=int, default=DEFAULT_PORT,
+                       help=argparse.SUPPRESS)
+
+    # Client mode arguments
+    parser.add_argument("-B", "--payload-bytes", type=int, default=None,
+                       help=argparse.SUPPRESS)
+    parser.add_argument("-s", "--src-ip", default=DEFAULT_SRC_IP,
+                       help=argparse.SUPPRESS)
+    parser.add_argument("-d", "--dst-ip", default=DEFAULT_DST_IP,
+                       help=argparse.SUPPRESS)
+    parser.add_argument("-I", "--interval", type=float, default=0.1,
+                       help=argparse.SUPPRESS)
+    parser.add_argument("-n", "--iterations", type=int, default=1,
+                       help=argparse.SUPPRESS)
+    parser.add_argument("--unique-data", action="store_true",
+                       help=argparse.SUPPRESS)
+
+    # Server mode arguments
+    parser.add_argument("--bind-ip", default="0.0.0.0",
+                       help=argparse.SUPPRESS)
+
+    args = parser.parse_args()
+
+    # Validate arguments
+    if args.port < 1 or args.port > 65535:
+        print(f"Error: Port {args.port} is out of valid range (1-65535)")
+        sys.exit(1)
+
+    if args.mode == 'client':
+        if args.iterations < 1:
+            print(f"Error: Iterations must be at least 1, "
+                  f"got {args.iterations}")
+            sys.exit(1)
+        if args.interval < 0:
+            print(f"Error: Interval cannot be negative, "
+                  f"got {args.interval}")
+            sys.exit(1)
+        if args.payload_bytes is not None and args.payload_bytes < 500:
+            print(f"Error: Payload bytes must be at least 500, "
+                  f"got {args.payload_bytes}")
+            sys.exit(1)
+
+    if args.mode == 'server':
+        # Run server
+        server = TCPServer(args.bind_ip, args.port)
+        server.start()
+    elif args.mode == 'client':
+        # Run client
+        client = TCPClient(args.src_ip, args.dst_ip, args.port)
+        success = client.connect_and_send(
+            max(0, int(args.payload_bytes)), args.iterations,
+            args.interval, args.unique_data)
+
+        # Summary
+        print(f"Client summary: payload_bytes={args.payload_bytes} "
+              f"iterations={args.iterations} success={success}")
+
+        sys.exit(success)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tests/udp_client.py b/tests/udp_client.py
new file mode 100755
index 000000000..cc67275f8
--- /dev/null
+++ b/tests/udp_client.py
@@ -0,0 +1,113 @@
+#!/usr/bin/env python3
+"""
+Scapy UDP client with MTU/payload control for testing fragmented UDP traffic.
+
+This module provides functionality to send fragmented UDP packets using Scapy,
+allowing control over MTU, payload size, and fragmentation behavior.
+"""
+import time
+import argparse
+import sys
+from scapy.all import IP, UDP, Raw, send, fragment
+
+# Defaults for same logical switch topology
+DEFAULT_SRC_IP = "172.16.1.3"
+DEFAULT_DST_IP = "172.16.1.2"
+
+
+def read_iface_mtu(ifname: str):
+    """Return MTU of interface or None if not available."""
+    try:
+        path = f"/sys/class/net/{ifname}/mtu"
+        with open(path, "r", encoding="utf-8") as f:
+            return int(f.read().strip())
+    except Exception:
+        return None
+
+
+def main():
+    """Main function to parse arguments and send fragmented UDP packets."""
+    parser = argparse.ArgumentParser(
+        description="Scapy UDP client with MTU/payload control")
+    parser.add_argument("-M", "--mtu", type=int, default=None,
+        help="Target MTU; payload ~ mtu-28 (IPv4+UDP).")
+    parser.add_argument("-B", "--payload-bytes", type=int, default=None,
+        help="Total UDP payload bytes (override default).")
+    parser.add_argument("-S", "--sport", type=int, default=4242,
+        help="UDP source port")
+    parser.add_argument("-D", "--dport", type=int, default=4242,
+        help="UDP destination port")
+    parser.add_argument("-s", "--src-ip", default=DEFAULT_SRC_IP,
+        help="Source IPv4 address")
+    parser.add_argument("-d", "--dst-ip", default=DEFAULT_DST_IP,
+        help="Destination IPv4 address")
+    parser.add_argument("-i", "--iface", default="client",
+        help="Egress interface (default: 'client').")
+    parser.add_argument("-I", "--interval", type=float, default=0.1,
+        help="Seconds between sends.")
+    parser.add_argument("-n", "--iterations", type=int, default=1,
+        help="Number of datagrams to send.")
+    args = parser.parse_args()
+
+    # Derive fragment size: for link MTU M, fragsize should typically be M-20
+    # (IP header)
+    if args.mtu is not None:
+        fragsize = max(68, int(args.mtu) - 20)
+    else:
+        fragsize = 1480  # default for 1500 MTU
+
+    # Build payload; size can be user-controlled or synthesized to ensure
+    # fragmentation
+    if args.payload_bytes is not None:
+        payload_len = max(0, int(args.payload_bytes))
+        payload = b"x" * payload_len
+    elif args.mtu is not None:
+        # Ensure payload exceeds fragsize-8 (UDP header) so we actually
+        # fragment.
+        base_len = max(0, int(args.mtu) - 28)
+        min_len_to_fragment = max(0, fragsize - 8 + 1)
+        payload_len = (base_len if base_len > min_len_to_fragment else
+                       fragsize * 2)
+        payload = b"x" * payload_len
+    else:
+        # No explicit size; synthesize a payload big enough to fragment at
+        # default fragsize
+        payload_len = fragsize * 2
+        payload = b"x" * payload_len
+
+    # Construct full IP/UDP packet and fragment it explicitly
+    ip_layer = IP(src=args.src_ip, dst=args.dst_ip)
+    udp_layer = UDP(sport=args.sport, dport=args.dport)
+    full_packet = ip_layer / udp_layer / Raw(load=payload)
+    frags = fragment(full_packet, fragsize=fragsize)
+
+    total_fragments_per_send = len(frags)
+    for _ in range(max(0, args.iterations)):
+        try:
+            send(frags, iface=args.iface, return_packets=True, verbose=False)
+        except OSError as e:
+            # Errno 90: Message too long (likely iface MTU < chosen --mtu)
+            if getattr(e, "errno", None) == 90:
+                iface_mtu = read_iface_mtu(args.iface)
+                mtu_note = (f"iface_mtu={iface_mtu}" if iface_mtu is not None
+                            else "iface_mtu=unknown")
+                print("ERROR: packet exceeds interface MTU. "
+                    f"iface={args.iface} {mtu_note} chosen_mtu="
+                    f"{args.mtu if args.mtu is not None else 1500} "
+                    f"fragsize={fragsize}. Set --mtu to the interface MTU.",
+                    file=sys.stderr)
+                sys.exit(2)
+            raise
+        time.sleep(args.interval)
+
+    # Summary
+    mtu_print = args.mtu if args.mtu is not None else 1500
+    total_frags = total_fragments_per_send * max(0, args.iterations)
+    print(f"payload_bytes={payload_len} mtu={mtu_print} fragsize={fragsize} "
+        f"fragments_per_datagram={total_fragments_per_send} "
+        f"total_fragments_sent={total_frags}")
+
+
+if __name__ == "__main__":
+    main()
+    sys.exit(0)
-- 
2.43.0

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