diff --git a/net/mctp/Kconfig b/net/mctp/Kconfig
index 3a5c0e70da77..d8d3413a37f7 100644
--- a/net/mctp/Kconfig
+++ b/net/mctp/Kconfig
@@ -14,6 +14,7 @@ menuconfig MCTP
 
 config MCTP_TEST
         bool "MCTP core tests" if !KUNIT_ALL_TESTS
+        select MCTP_FLOWS
         depends on MCTP=y && KUNIT=y
         default KUNIT_ALL_TESTS
 
diff --git a/net/mctp/test/route-test.c b/net/mctp/test/route-test.c
index bad084525f17..eb7e9ac95612 100644
--- a/net/mctp/test/route-test.c
+++ b/net/mctp/test/route-test.c
@@ -837,6 +837,140 @@ static void mctp_test_route_input_multiple_nets_key(struct kunit *test)
 	mctp_test_route_input_multiple_nets_key_fini(test, &t2);
 }
 
+#if IS_ENABLED(CONFIG_MCTP_FLOWS)
+
+static void mctp_test_flow_init(struct kunit *test,
+				struct mctp_test_dev **devp,
+				struct mctp_test_route **rtp,
+				struct socket **sock,
+				struct sk_buff **skbp,
+				unsigned int len)
+{
+	struct mctp_test_route *rt;
+	struct mctp_test_dev *dev;
+	struct sk_buff *skb;
+
+	/* we have a slightly odd routing setup here; the test route
+	 * is for EID 8, which is our local EID. We don't do a routing
+	 * lookup, so that's fine - all we require is a path through
+	 * mctp_local_output, which will call rt->output on whatever
+	 * route we provide
+	 */
+	__mctp_route_test_init(test, &dev, &rt, sock, MCTP_NET_ANY);
+
+	/* Assign a single EID. ->addrs is freed on mctp netdev release */
+	dev->mdev->addrs = kmalloc(sizeof(u8), GFP_KERNEL);
+	dev->mdev->num_addrs = 1;
+	dev->mdev->addrs[0] = 8;
+
+	skb = alloc_skb(len + sizeof(struct mctp_hdr) + 1, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, skb);
+	__mctp_cb(skb);
+	skb_reserve(skb, sizeof(struct mctp_hdr) + 1);
+	memset(skb_put(skb, len), 0, len);
+
+	/* take a ref for the route, we'll decrement in local output */
+	refcount_inc(&rt->rt.refs);
+
+	*devp = dev;
+	*rtp = rt;
+	*skbp = skb;
+}
+
+static void mctp_test_flow_fini(struct kunit *test,
+				struct mctp_test_dev *dev,
+				struct mctp_test_route *rt,
+				struct socket *sock)
+{
+	__mctp_route_test_fini(test, dev, rt, sock);
+}
+
+/* test that an outgoing skb has the correct MCTP extension data set */
+static void mctp_test_packet_flow(struct kunit *test)
+{
+	struct sk_buff *skb, *skb2;
+	struct mctp_test_route *rt;
+	struct mctp_test_dev *dev;
+	struct mctp_flow *flow;
+	struct socket *sock;
+	u8 dst = 8;
+	int n, rc;
+
+	mctp_test_flow_init(test, &dev, &rt, &sock, &skb, 30);
+
+	rc = mctp_local_output(sock->sk, &rt->rt, skb, dst, MCTP_TAG_OWNER);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	n = rt->pkts.qlen;
+	KUNIT_ASSERT_EQ(test, n, 1);
+
+	skb2 = skb_dequeue(&rt->pkts);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, skb2);
+
+	flow = skb_ext_find(skb2, SKB_EXT_MCTP);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, flow);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, flow->key);
+	KUNIT_ASSERT_PTR_EQ(test, flow->key->sk, sock->sk);
+
+	kfree_skb(skb2);
+	mctp_test_flow_fini(test, dev, rt, sock);
+}
+
+/* test that outgoing skbs, after fragmentation, all have the correct MCTP
+ * extension data set.
+ */
+static void mctp_test_fragment_flow(struct kunit *test)
+{
+	struct mctp_flow *flows[2];
+	struct sk_buff *tx_skbs[2];
+	struct mctp_test_route *rt;
+	struct mctp_test_dev *dev;
+	struct sk_buff *skb;
+	struct socket *sock;
+	u8 dst = 8;
+	int n, rc;
+
+	mctp_test_flow_init(test, &dev, &rt, &sock, &skb, 100);
+
+	rc = mctp_local_output(sock->sk, &rt->rt, skb, dst, MCTP_TAG_OWNER);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	n = rt->pkts.qlen;
+	KUNIT_ASSERT_EQ(test, n, 2);
+
+	/* both resulting packets should have the same flow data */
+	tx_skbs[0] = skb_dequeue(&rt->pkts);
+	tx_skbs[1] = skb_dequeue(&rt->pkts);
+
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, tx_skbs[0]);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, tx_skbs[1]);
+
+	flows[0] = skb_ext_find(tx_skbs[0], SKB_EXT_MCTP);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, flows[0]);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, flows[0]->key);
+	KUNIT_ASSERT_PTR_EQ(test, flows[0]->key->sk, sock->sk);
+
+	flows[1] = skb_ext_find(tx_skbs[1], SKB_EXT_MCTP);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, flows[1]);
+	KUNIT_ASSERT_PTR_EQ(test, flows[1]->key, flows[0]->key);
+
+	kfree_skb(tx_skbs[0]);
+	kfree_skb(tx_skbs[1]);
+	mctp_test_flow_fini(test, dev, rt, sock);
+}
+
+#else
+static void mctp_test_packet_flow(struct kunit *test)
+{
+	kunit_skip(test, "Requires CONFIG_MCTP_FLOWS=y");
+}
+
+static void mctp_test_fragment_flow(struct kunit *test)
+{
+	kunit_skip(test, "Requires CONFIG_MCTP_FLOWS=y");
+}
+#endif
+
 static struct kunit_case mctp_test_cases[] = {
 	KUNIT_CASE_PARAM(mctp_test_fragment, mctp_frag_gen_params),
 	KUNIT_CASE_PARAM(mctp_test_rx_input, mctp_rx_input_gen_params),
@@ -847,6 +981,8 @@ static struct kunit_case mctp_test_cases[] = {
 			 mctp_route_input_sk_keys_gen_params),
 	KUNIT_CASE(mctp_test_route_input_multiple_nets_bind),
 	KUNIT_CASE(mctp_test_route_input_multiple_nets_key),
+	KUNIT_CASE(mctp_test_packet_flow),
+	KUNIT_CASE(mctp_test_fragment_flow),
 	{}
 };
 
diff --git a/tools/testing/kunit/configs/all_tests.config b/tools/testing/kunit/configs/all_tests.config
index 12da4c493867..a6cf69a665e8 100644
--- a/tools/testing/kunit/configs/all_tests.config
+++ b/tools/testing/kunit/configs/all_tests.config
@@ -23,6 +23,7 @@ CONFIG_USB4=y
 
 CONFIG_NET=y
 CONFIG_MCTP=y
+CONFIG_MCTP_FLOWS=y
 
 CONFIG_INET=y
 CONFIG_MPTCP=y