[PATCH net-next v2 0/2] Add support for externally validated neighbor entries

[PATCH net-next v2 0/2] Add support for externally validated neighbor entries

[Ido Schimmel]

Patch #1 adds a new neighbor flag ("extern_valid") that prevents the
kernel from invalidating or removing a neighbor entry, while allowing
the kernel to notify user space when the entry becomes reachable. See
motivation and implementation details in the commit message.

Patch #2 adds a selftest.

Changes since v1 [1]:

* Patch #1: s/neigbor/neighbor/ in comment.
* Patch #1: Do not flush "extern_valid" entries upon carrier down.
* Patch #1: Reword some parts of the commit message.
* Patch #2: Fix various shellcheck warnings.
* Patch #2: Add tests for interface and carrier down.

[1] https://lore.kernel.org/netdev/20250611141551.462569-1-idosch@nvidia.com/

Ido Schimmel (2):
  neighbor: Add NTF_EXT_VALIDATED flag for externally validated entries
  selftests: net: Add a selftest for externally validated neighbor
    entries

 Documentation/netlink/specs/rt-neigh.yaml |   1 +
 include/net/neighbour.h                   |   4 +-
 include/uapi/linux/neighbour.h            |   5 +
 net/core/neighbour.c                      |  79 ++++-
 tools/testing/selftests/net/Makefile      |   1 +
 tools/testing/selftests/net/test_neigh.sh | 366 ++++++++++++++++++++++
 6 files changed, 445 insertions(+), 11 deletions(-)
 create mode 100755 tools/testing/selftests/net/test_neigh.sh

-- 
2.49.0

[PATCH net-next v2 1/2] neighbor: Add NTF_EXT_VALIDATED flag for externally validated entries

[Ido Schimmel]

tl;dr
=====

Add a new neighbor flag ("extern_valid") that can be used to indicate to
the kernel that a neighbor entry was learned and determined to be valid
externally. The kernel will not try to remove or invalidate such an
entry, leaving these decisions to the user space control plane. This is
needed for EVPN multi-homing where a neighbor entry for a multi-homed
host needs to be synced across all the VTEPs among which the host is
multi-homed.

Background
==========

In a typical EVPN multi-homing setup each host is multi-homed using a
set of links called ES (Ethernet Segment, i.e., LAG) to multiple leaf
switches (VTEPs). VTEPs that are connected to the same ES are called ES
peers.

When a neighbor entry is learned on a VTEP, it is distributed to both ES
peers and remote VTEPs using EVPN MAC/IP advertisement routes. ES peers
use the neighbor entry when routing traffic towards the multi-homed host
and remote VTEPs use it for ARP/NS suppression.

Motivation
==========

If the ES link between a host and the VTEP on which the neighbor entry
was locally learned goes down, the EVPN MAC/IP advertisement route will
be withdrawn and the neighbor entries will be removed from both ES peers
and remote VTEPs. Routing towards the multi-homed host and ARP/NS
suppression can fail until another ES peer locally learns the neighbor
entry and distributes it via an EVPN MAC/IP advertisement route.

"draft-rbickhart-evpn-ip-mac-proxy-adv-03" [1] suggests avoiding these
intermittent failures by having the ES peers install the neighbor
entries as before, but also injecting EVPN MAC/IP advertisement routes
with a proxy indication. When the previously mentioned ES link goes down
and the original EVPN MAC/IP advertisement route is withdrawn, the ES
peers will not withdraw their neighbor entries, but instead start aging
timers for the proxy indication.

If an ES peer locally learns the neighbor entry (i.e., it becomes
"reachable"), it will restart its aging timer for the entry and emit an
EVPN MAC/IP advertisement route without a proxy indication. An ES peer
will stop its aging timer for the proxy indication if it observes the
removal of the proxy indication from at least one of the ES peers
advertising the entry.

In the event that the aging timer for the proxy indication expired, an
ES peer will withdraw its EVPN MAC/IP advertisement route. If the timer
expired on all ES peers and they all withdrew their proxy
advertisements, the neighbor entry will be completely removed from the
EVPN fabric.

Implementation
==============

In the above scheme, when the control plane (e.g., FRR) advertises a
neighbor entry with a proxy indication, it expects the corresponding
entry in the data plane (i.e., the kernel) to remain valid and not be
removed due to garbage collection or loss of carrier. The control plane
also expects the kernel to notify it if the entry was learned locally
(i.e., became "reachable") so that it will remove the proxy indication
from the EVPN MAC/IP advertisement route. That is why these entries
cannot be programmed with dummy states such as "permanent" or "noarp".

Instead, add a new neighbor flag ("extern_valid") which indicates that
the entry was learned and determined to be valid externally and should
not be removed or invalidated by the kernel. The kernel can probe the
entry and notify user space when it becomes "reachable" (it is initially
installed as "stale"). However, if the kernel does not receive a
confirmation, have it return the entry to the "stale" state instead of
the "failed" state.

In other words, an entry marked with the "extern_valid" flag behaves
like any other dynamically learned entry other than the fact that the
kernel cannot remove or invalidate it.

One can argue that the "extern_valid" flag should not prevent garbage
collection and that instead a neighbor entry should be programmed with
both the "extern_valid" and "extern_learn" flags. There are two reasons
for not doing that:

1. Unclear why a control plane would like to program an entry that the
   kernel cannot invalidate but can completely remove.

2. The "extern_learn" flag is used by FRR for neighbor entries learned
   on remote VTEPs (for ARP/NS suppression) whereas here we are
   concerned with local entries. This distinction is currently irrelevant
   for the kernel, but might be relevant in the future.

Given that the flag only makes sense when the neighbor has a valid
state, reject attempts to add a neighbor with an invalid state and with
this flag set. For example:

 # ip neigh add 192.0.2.1 nud none dev br0.10 extern_valid
 Error: Cannot create externally validated neighbor with an invalid state.
 # ip neigh add 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid
 # ip neigh replace 192.0.2.1 nud failed dev br0.10 extern_valid
 Error: Cannot mark neighbor as externally validated with an invalid state.

The above means that a neighbor cannot be created with the
"extern_valid" flag and flags such as "use" or "managed" as they result
in a neighbor being created with an invalid state ("none") and
immediately getting probed:

 # ip neigh add 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use
 Error: Cannot create externally validated neighbor with an invalid state.

However, these flags can be used together with "extern_valid" after the
neighbor was created with a valid state:

 # ip neigh add 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid
 # ip neigh replace 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use

One consequence of preventing the kernel from invalidating a neighbor
entry is that by default it will only try to determine reachability
using unicast probes. This can be changed using the "mcast_resolicit"
sysctl:

 # sysctl net.ipv4.neigh.br0/10.mcast_resolicit
 0
 # tcpdump -nn -e -i br0.10 -Q out arp &
 # ip neigh replace 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use
 62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 # sysctl -wq net.ipv4.neigh.br0/10.mcast_resolicit=3
 # ip neigh replace 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use
 62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
 62:50:1d:11:93:6f > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28

iproute2 patches can be found here [2].

[1] https://datatracker.ietf.org/doc/html/draft-rbickhart-evpn-ip-mac-proxy-adv-03
[2] https://github.com/idosch/iproute2/tree/submit/extern_valid_v1

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---

Notes:
    v2:
    
    * s/neigbor/neighbor/ in comment.
    * Do not flush "extern_valid" entries upon carrier down.
    * Reword some parts of the commit message.

 Documentation/netlink/specs/rt-neigh.yaml |  1 +
 include/net/neighbour.h                   |  4 +-
 include/uapi/linux/neighbour.h            |  5 ++
 net/core/neighbour.c                      | 79 ++++++++++++++++++++---
 4 files changed, 78 insertions(+), 11 deletions(-)

diff --git a/Documentation/netlink/specs/rt-neigh.yaml b/Documentation/netlink/specs/rt-neigh.yaml
index 25cc2d528d2f..30a9ee16f128 100644
--- a/Documentation/netlink/specs/rt-neigh.yaml
+++ b/Documentation/netlink/specs/rt-neigh.yaml
@@ -79,6 +79,7 @@ definitions:
     entries:
       - managed
       - locked
+      - ext-validated
   -
     name: rtm-type
     type: enum
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index c7ce5ec7be23..7e865b14749d 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -261,13 +261,15 @@ static inline void *neighbour_priv(const struct neighbour *n)
 #define NEIGH_UPDATE_F_EXT_LEARNED		BIT(5)
 #define NEIGH_UPDATE_F_ISROUTER			BIT(6)
 #define NEIGH_UPDATE_F_ADMIN			BIT(7)
+#define NEIGH_UPDATE_F_EXT_VALIDATED		BIT(8)
 
 /* In-kernel representation for NDA_FLAGS_EXT flags: */
 #define NTF_OLD_MASK		0xff
 #define NTF_EXT_SHIFT		8
-#define NTF_EXT_MASK		(NTF_EXT_MANAGED)
+#define NTF_EXT_MASK		(NTF_EXT_MANAGED | NTF_EXT_EXT_VALIDATED)
 
 #define NTF_MANAGED		(NTF_EXT_MANAGED << NTF_EXT_SHIFT)
+#define NTF_EXT_VALIDATED	(NTF_EXT_EXT_VALIDATED << NTF_EXT_SHIFT)
 
 extern const struct nla_policy nda_policy[];
 
diff --git a/include/uapi/linux/neighbour.h b/include/uapi/linux/neighbour.h
index b851c36ad25d..c34a81245f87 100644
--- a/include/uapi/linux/neighbour.h
+++ b/include/uapi/linux/neighbour.h
@@ -54,6 +54,7 @@ enum {
 /* Extended flags under NDA_FLAGS_EXT: */
 #define NTF_EXT_MANAGED		(1 << 0)
 #define NTF_EXT_LOCKED		(1 << 1)
+#define NTF_EXT_EXT_VALIDATED	(1 << 2)
 
 /*
  *	Neighbor Cache Entry States.
@@ -92,6 +93,10 @@ enum {
  * bridge in response to a host trying to communicate via a locked bridge port
  * with MAB enabled. Their purpose is to notify user space that a host requires
  * authentication.
+ *
+ * NTF_EXT_EXT_VALIDATED flagged neighbor entries were externally validated by
+ * a user space control plane. The kernel will not remove or invalidate them,
+ * but it can probe them and notify user space when they become reachable.
  */
 
 struct nda_cacheinfo {
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 8ad9898f8e42..e5f0992ac364 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -154,11 +154,12 @@ static void neigh_update_gc_list(struct neighbour *n)
 	if (n->dead)
 		goto out;
 
-	/* remove from the gc list if new state is permanent or if neighbor
-	 * is externally learned; otherwise entry should be on the gc list
+	/* remove from the gc list if new state is permanent or if neighbor is
+	 * externally learned / validated; otherwise entry should be on the gc
+	 * list
 	 */
 	exempt_from_gc = n->nud_state & NUD_PERMANENT ||
-			 n->flags & NTF_EXT_LEARNED;
+			 n->flags & (NTF_EXT_LEARNED | NTF_EXT_VALIDATED);
 	on_gc_list = !list_empty(&n->gc_list);
 
 	if (exempt_from_gc && on_gc_list) {
@@ -205,6 +206,7 @@ static void neigh_update_flags(struct neighbour *neigh, u32 flags, int *notify,
 
 	ndm_flags  = (flags & NEIGH_UPDATE_F_EXT_LEARNED) ? NTF_EXT_LEARNED : 0;
 	ndm_flags |= (flags & NEIGH_UPDATE_F_MANAGED) ? NTF_MANAGED : 0;
+	ndm_flags |= (flags & NEIGH_UPDATE_F_EXT_VALIDATED) ? NTF_EXT_VALIDATED : 0;
 
 	if ((old_flags ^ ndm_flags) & NTF_EXT_LEARNED) {
 		if (ndm_flags & NTF_EXT_LEARNED)
@@ -222,6 +224,14 @@ static void neigh_update_flags(struct neighbour *neigh, u32 flags, int *notify,
 		*notify = 1;
 		*managed_update = true;
 	}
+	if ((old_flags ^ ndm_flags) & NTF_EXT_VALIDATED) {
+		if (ndm_flags & NTF_EXT_VALIDATED)
+			neigh->flags |= NTF_EXT_VALIDATED;
+		else
+			neigh->flags &= ~NTF_EXT_VALIDATED;
+		*notify = 1;
+		*gc_update = true;
+	}
 }
 
 bool neigh_remove_one(struct neighbour *n)
@@ -379,7 +389,9 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 	dev_head = neigh_get_dev_table(dev, tbl->family);
 
 	hlist_for_each_entry_safe(n, tmp, dev_head, dev_list) {
-		if (skip_perm && n->nud_state & NUD_PERMANENT)
+		if (skip_perm &&
+		    (n->nud_state & NUD_PERMANENT ||
+		     n->flags & NTF_EXT_VALIDATED))
 			continue;
 
 		hlist_del_rcu(&n->hash);
@@ -942,7 +954,8 @@ static void neigh_periodic_work(struct work_struct *work)
 
 			state = n->nud_state;
 			if ((state & (NUD_PERMANENT | NUD_IN_TIMER)) ||
-			    (n->flags & NTF_EXT_LEARNED)) {
+			    (n->flags &
+			     (NTF_EXT_LEARNED | NTF_EXT_VALIDATED))) {
 				write_unlock(&n->lock);
 				continue;
 			}
@@ -1095,9 +1108,15 @@ static void neigh_timer_handler(struct timer_list *t)
 
 	if ((neigh->nud_state & (NUD_INCOMPLETE | NUD_PROBE)) &&
 	    atomic_read(&neigh->probes) >= neigh_max_probes(neigh)) {
-		WRITE_ONCE(neigh->nud_state, NUD_FAILED);
+		if (neigh->nud_state == NUD_PROBE &&
+		    neigh->flags & NTF_EXT_VALIDATED) {
+			WRITE_ONCE(neigh->nud_state, NUD_STALE);
+			neigh->updated = jiffies;
+		} else {
+			WRITE_ONCE(neigh->nud_state, NUD_FAILED);
+			neigh_invalidate(neigh);
+		}
 		notify = 1;
-		neigh_invalidate(neigh);
 		goto out;
 	}
 
@@ -1245,6 +1264,8 @@ static void neigh_update_hhs(struct neighbour *neigh)
 				NTF_ROUTER flag.
 	NEIGH_UPDATE_F_ISROUTER	indicates if the neighbour is known as
 				a router.
+	NEIGH_UPDATE_F_EXT_VALIDATED means that the entry will not be removed
+				or invalidated.
 
    Caller MUST hold reference count on the entry.
  */
@@ -1979,7 +2000,7 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (ndm_flags & NTF_PROXY) {
 		struct pneigh_entry *pn;
 
-		if (ndm_flags & NTF_MANAGED) {
+		if (ndm_flags & (NTF_MANAGED | NTF_EXT_VALIDATED)) {
 			NL_SET_ERR_MSG(extack, "Invalid NTF_* flag combination");
 			goto out;
 		}
@@ -2010,7 +2031,8 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (neigh == NULL) {
 		bool ndm_permanent  = ndm->ndm_state & NUD_PERMANENT;
 		bool exempt_from_gc = ndm_permanent ||
-				      ndm_flags & NTF_EXT_LEARNED;
+				      ndm_flags & (NTF_EXT_LEARNED |
+						   NTF_EXT_VALIDATED);
 
 		if (!(nlh->nlmsg_flags & NLM_F_CREATE)) {
 			err = -ENOENT;
@@ -2021,10 +2043,27 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 			err = -EINVAL;
 			goto out;
 		}
+		if (ndm_flags & NTF_EXT_VALIDATED) {
+			u8 state = ndm->ndm_state;
+
+			/* NTF_USE and NTF_MANAGED will result in the neighbor
+			 * being created with an invalid state (NUD_NONE).
+			 */
+			if (ndm_flags & (NTF_USE | NTF_MANAGED))
+				state = NUD_NONE;
+
+			if (!(state & NUD_VALID)) {
+				NL_SET_ERR_MSG(extack,
+					       "Cannot create externally validated neighbor with an invalid state");
+				err = -EINVAL;
+				goto out;
+			}
+		}
 
 		neigh = ___neigh_create(tbl, dst, dev,
 					ndm_flags &
-					(NTF_EXT_LEARNED | NTF_MANAGED),
+					(NTF_EXT_LEARNED | NTF_MANAGED |
+					 NTF_EXT_VALIDATED),
 					exempt_from_gc, true);
 		if (IS_ERR(neigh)) {
 			err = PTR_ERR(neigh);
@@ -2036,6 +2075,24 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 			neigh_release(neigh);
 			goto out;
 		}
+		if (ndm_flags & NTF_EXT_VALIDATED) {
+			u8 state = ndm->ndm_state;
+
+			/* NTF_USE and NTF_MANAGED do not update the existing
+			 * state other than clearing it if it was
+			 * NUD_PERMANENT.
+			 */
+			if (ndm_flags & (NTF_USE | NTF_MANAGED))
+				state = READ_ONCE(neigh->nud_state) & ~NUD_PERMANENT;
+
+			if (!(state & NUD_VALID)) {
+				NL_SET_ERR_MSG(extack,
+					       "Cannot mark neighbor as externally validated with an invalid state");
+				err = -EINVAL;
+				neigh_release(neigh);
+				goto out;
+			}
+		}
 
 		if (!(nlh->nlmsg_flags & NLM_F_REPLACE))
 			flags &= ~(NEIGH_UPDATE_F_OVERRIDE |
@@ -2052,6 +2109,8 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
 		flags |= NEIGH_UPDATE_F_MANAGED;
 	if (ndm_flags & NTF_USE)
 		flags |= NEIGH_UPDATE_F_USE;
+	if (ndm_flags & NTF_EXT_VALIDATED)
+		flags |= NEIGH_UPDATE_F_EXT_VALIDATED;
 
 	err = __neigh_update(neigh, lladdr, ndm->ndm_state, flags,
 			     NETLINK_CB(skb).portid, extack);
-- 
2.49.0

Re: [PATCH net-next v2 1/2] neighbor: Add NTF_EXT_VALIDATED flag for externally validated entries

[Daniel Borkmann]

On 6/26/25 9:31 AM, Ido Schimmel wrote:
[...]
> However, these flags can be used together with "extern_valid" after the
> neighbor was created with a valid state:
> 
>   # ip neigh add 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid
>   # ip neigh replace 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use
> 
> One consequence of preventing the kernel from invalidating a neighbor
> entry is that by default it will only try to determine reachability
> using unicast probes. This can be changed using the "mcast_resolicit"
> sysctl:
> 
>   # sysctl net.ipv4.neigh.br0/10.mcast_resolicit
>   0
>   # tcpdump -nn -e -i br0.10 -Q out arp &
>   # ip neigh replace 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use
>   62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   # sysctl -wq net.ipv4.neigh.br0/10.mcast_resolicit=3
>   # ip neigh replace 192.0.2.1 lladdr 00:11:22:33:44:55 nud stale dev br0.10 extern_valid use
>   62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > 00:11:22:33:44:55, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
>   62:50:1d:11:93:6f > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 42: Request who-has 192.0.2.1 tell 192.0.2.2, length 28
> 
> iproute2 patches can be found here [2].
> 
> [1] https://datatracker.ietf.org/doc/html/draft-rbickhart-evpn-ip-mac-proxy-adv-03
> [2] https://github.com/idosch/iproute2/tree/submit/extern_valid_v1
> 
> Signed-off-by: Ido Schimmel <idosch@nvidia.com>

lgtm

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

[PATCH net-next v2 2/2] selftests: net: Add a selftest for externally validated neighbor entries

[Ido Schimmel]

Add test cases for externally validated neighbor entries, testing both
IPv4 and IPv6. Name the file "test_neigh.sh" so that it could be
possibly extended in the future with more neighbor test cases.

Example output:

 # ./test_neigh.sh
 TEST: IPv4 "extern_valid" flag: Add entry                           [ OK ]
 TEST: IPv4 "extern_valid" flag: Add with an invalid state           [ OK ]
 TEST: IPv4 "extern_valid" flag: Add with "use" flag                 [ OK ]
 TEST: IPv4 "extern_valid" flag: Replace entry                       [ OK ]
 TEST: IPv4 "extern_valid" flag: Replace entry with "managed" flag   [ OK ]
 TEST: IPv4 "extern_valid" flag: Replace with an invalid state       [ OK ]
 TEST: IPv4 "extern_valid" flag: Interface down                      [ OK ]
 TEST: IPv4 "extern_valid" flag: Carrier down                        [ OK ]
 TEST: IPv4 "extern_valid" flag: Transition to "reachable" state     [ OK ]
 TEST: IPv4 "extern_valid" flag: Transition back to "stale" state    [ OK ]
 TEST: IPv4 "extern_valid" flag: Forced garbage collection           [ OK ]
 TEST: IPv4 "extern_valid" flag: Periodic garbage collection         [ OK ]
 TEST: IPv6 "extern_valid" flag: Add entry                           [ OK ]
 TEST: IPv6 "extern_valid" flag: Add with an invalid state           [ OK ]
 TEST: IPv6 "extern_valid" flag: Add with "use" flag                 [ OK ]
 TEST: IPv6 "extern_valid" flag: Replace entry                       [ OK ]
 TEST: IPv6 "extern_valid" flag: Replace entry with "managed" flag   [ OK ]
 TEST: IPv6 "extern_valid" flag: Replace with an invalid state       [ OK ]
 TEST: IPv6 "extern_valid" flag: Interface down                      [ OK ]
 TEST: IPv6 "extern_valid" flag: Carrier down                        [ OK ]
 TEST: IPv6 "extern_valid" flag: Transition to "reachable" state     [ OK ]
 TEST: IPv6 "extern_valid" flag: Transition back to "stale" state    [ OK ]
 TEST: IPv6 "extern_valid" flag: Forced garbage collection           [ OK ]
 TEST: IPv6 "extern_valid" flag: Periodic garbage collection         [ OK ]

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---

Notes:
    v2:
    
    * Fix various shellcheck warnings.
    * Add tests for interface and carrier down.

 tools/testing/selftests/net/Makefile      |   1 +
 tools/testing/selftests/net/test_neigh.sh | 366 ++++++++++++++++++++++
 2 files changed, 367 insertions(+)
 create mode 100755 tools/testing/selftests/net/test_neigh.sh

diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
index 227f9e067d25..543776596529 100644
--- a/tools/testing/selftests/net/Makefile
+++ b/tools/testing/selftests/net/Makefile
@@ -100,6 +100,7 @@ TEST_PROGS += test_vxlan_mdb.sh
 TEST_PROGS += test_bridge_neigh_suppress.sh
 TEST_PROGS += test_vxlan_nolocalbypass.sh
 TEST_PROGS += test_bridge_backup_port.sh
+TEST_PROGS += test_neigh.sh
 TEST_PROGS += fdb_flush.sh fdb_notify.sh
 TEST_PROGS += fq_band_pktlimit.sh
 TEST_PROGS += vlan_hw_filter.sh
diff --git a/tools/testing/selftests/net/test_neigh.sh b/tools/testing/selftests/net/test_neigh.sh
new file mode 100755
index 000000000000..388056472b5b
--- /dev/null
+++ b/tools/testing/selftests/net/test_neigh.sh
@@ -0,0 +1,366 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+source lib.sh
+TESTS="
+	extern_valid_ipv4
+	extern_valid_ipv6
+"
+VERBOSE=0
+
+################################################################################
+# Utilities
+
+run_cmd()
+{
+	local cmd="$1"
+	local out
+	local stderr="2>/dev/null"
+
+	if [ "$VERBOSE" = "1" ]; then
+		echo "COMMAND: $cmd"
+		stderr=
+	fi
+
+	out=$(eval "$cmd" "$stderr")
+	rc=$?
+	if [ "$VERBOSE" -eq 1 ] && [ -n "$out" ]; then
+		echo "    $out"
+	fi
+
+	return $rc
+}
+
+################################################################################
+# Setup
+
+setup()
+{
+	set -e
+
+	setup_ns ns1 ns2
+
+	ip -n "$ns1" link add veth0 type veth peer name veth1 netns "$ns2"
+	ip -n "$ns1" link set dev veth0 up
+	ip -n "$ns2" link set dev veth1 up
+
+	ip -n "$ns1" address add 192.0.2.1/24 dev veth0
+	ip -n "$ns1" address add 2001:db8:1::1/64 dev veth0 nodad
+	ip -n "$ns2" address add 192.0.2.2/24 dev veth1
+	ip -n "$ns2" address add 2001:db8:1::2/64 dev veth1 nodad
+
+	ip netns exec "$ns1" sysctl -qw net.ipv6.conf.all.keep_addr_on_down=1
+	ip netns exec "$ns2" sysctl -qw net.ipv6.conf.all.keep_addr_on_down=1
+
+	sleep 5
+
+	set +e
+}
+
+exit_cleanup_all()
+{
+	cleanup_all_ns
+	exit "${EXIT_STATUS}"
+}
+
+################################################################################
+# Tests
+
+extern_valid_common()
+{
+	local af_str=$1; shift
+	local ip_addr=$1; shift
+	local tbl_name=$1; shift
+	local subnet=$1; shift
+	local mac
+
+	mac=$(ip -n "$ns2" -j link show dev veth1 | jq -r '.[]["address"]')
+
+	RET=0
+
+	# Check that simple addition works.
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_err $? "No \"extern_valid\" flag after addition"
+
+	log_test "$af_str \"extern_valid\" flag: Add entry"
+
+	RET=0
+
+	# Check that an entry cannot be added with "extern_valid" flag and an
+	# invalid state.
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr nud none dev veth0 extern_valid"
+	check_fail $? "Managed to add an entry with \"extern_valid\" flag and an invalid state"
+
+	log_test "$af_str \"extern_valid\" flag: Add with an invalid state"
+
+	RET=0
+
+	# Check that entry cannot be added with both "extern_valid" flag and
+	# "use" / "managed" flag.
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid use"
+	check_fail $? "Managed to add an entry with \"extern_valid\" flag and \"use\" flag"
+
+	log_test "$af_str \"extern_valid\" flag: Add with \"use\" flag"
+
+	RET=0
+
+	# Check that "extern_valid" flag can be toggled using replace.
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0"
+	run_cmd "ip -n $ns1 neigh replace $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_err $? "Did not manage to set \"extern_valid\" flag with replace"
+	run_cmd "ip -n $ns1 neigh replace $ip_addr lladdr $mac nud stale dev veth0"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_fail $? "Did not manage to clear \"extern_valid\" flag with replace"
+
+	log_test "$af_str \"extern_valid\" flag: Replace entry"
+
+	RET=0
+
+	# Check that an existing "extern_valid" entry can be marked as
+	# "managed".
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh replace $ip_addr lladdr $mac nud stale dev veth0 extern_valid managed"
+	check_err $? "Did not manage to add \"managed\" flag to an existing \"extern_valid\" entry"
+
+	log_test "$af_str \"extern_valid\" flag: Replace entry with \"managed\" flag"
+
+	RET=0
+
+	# Check that entry cannot be replaced with "extern_valid" flag and an
+	# invalid state.
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh replace $ip_addr nud none dev veth0 extern_valid"
+	check_fail $? "Managed to replace an entry with \"extern_valid\" flag and an invalid state"
+
+	log_test "$af_str \"extern_valid\" flag: Replace with an invalid state"
+
+	RET=0
+
+	# Check that an "extern_valid" entry is flushed when the interface is
+	# put administratively down.
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 link set dev veth0 down"
+	run_cmd "ip -n $ns1 link set dev veth0 up"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0"
+	check_fail $? "\"extern_valid\" entry not flushed upon interface down"
+
+	log_test "$af_str \"extern_valid\" flag: Interface down"
+
+	RET=0
+
+	# Check that an "extern_valid" entry is not flushed when the interface
+	# loses its carrier.
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns2 link set dev veth1 down"
+	run_cmd "ip -n $ns2 link set dev veth1 up"
+	run_cmd "sleep 2"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0"
+	check_err $? "\"extern_valid\" entry flushed upon carrier down"
+
+	log_test "$af_str \"extern_valid\" flag: Carrier down"
+
+	RET=0
+
+	# Check that when entry transitions to "reachable" state it maintains
+	# the "extern_valid" flag. Wait "delay_probe" seconds for ARP request /
+	# NS to be sent.
+	local delay_probe
+
+	delay_probe=$(ip -n "$ns1" -j ntable show dev veth0 name "$tbl_name" | jq '.[]["delay_probe"]')
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh replace $ip_addr lladdr $mac nud stale dev veth0 extern_valid use"
+	run_cmd "sleep $((delay_probe / 1000 + 2))"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"REACHABLE\""
+	check_err $? "Entry did not transition to \"reachable\" state"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_err $? "Entry did not maintain \"extern_valid\" flag after transition to \"reachable\" state"
+
+	log_test "$af_str \"extern_valid\" flag: Transition to \"reachable\" state"
+
+	RET=0
+
+	# Drop all packets, trigger resolution and check that entry goes back
+	# to "stale" state instead of "failed".
+	local mcast_reprobes
+	local retrans_time
+	local ucast_probes
+	local app_probes
+	local probes
+	local delay
+
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	run_cmd "tc -n $ns2 qdisc add dev veth1 clsact"
+	run_cmd "tc -n $ns2 filter add dev veth1 ingress proto all matchall action drop"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh replace $ip_addr lladdr $mac nud stale dev veth0 extern_valid use"
+	retrans_time=$(ip -n "$ns1" -j ntable show dev veth0 name "$tbl_name" | jq '.[]["retrans"]')
+	ucast_probes=$(ip -n "$ns1" -j ntable show dev veth0 name "$tbl_name" | jq '.[]["ucast_probes"]')
+	app_probes=$(ip -n "$ns1" -j ntable show dev veth0 name "$tbl_name" | jq '.[]["app_probes"]')
+	mcast_reprobes=$(ip -n "$ns1" -j ntable show dev veth0 name "$tbl_name" | jq '.[]["mcast_reprobes"]')
+	delay=$((delay_probe + (ucast_probes + app_probes + mcast_reprobes) * retrans_time))
+	run_cmd "sleep $((delay / 1000 + 2))"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"STALE\""
+	check_err $? "Entry did not return to \"stale\" state"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_err $? "Entry did not maintain \"extern_valid\" flag after returning to \"stale\" state"
+	probes=$(ip -n "$ns1" -j -s neigh get "$ip_addr" dev veth0 | jq '.[]["probes"]')
+	if [[ $probes -eq 0 ]]; then
+		check_err 1 "No probes were sent"
+	fi
+
+	log_test "$af_str \"extern_valid\" flag: Transition back to \"stale\" state"
+
+	run_cmd "tc -n $ns2 qdisc del dev veth1 clsact"
+
+	RET=0
+
+	# Forced garbage collection runs whenever the number of entries is
+	# larger than "thresh3" and deletes stale entries that have not been
+	# updated in the last 5 seconds.
+	#
+	# Check that an "extern_valid" entry survives a forced garbage
+	# collection. Add an entry, wait 5 seconds and add more entries than
+	# "thresh3" so that forced garbage collection will run.
+	#
+	# Note that the garbage collection thresholds are global resources and
+	# that changes in the initial namespace affect all the namespaces.
+	local forced_gc_runs_t0
+	local forced_gc_runs_t1
+	local orig_thresh1
+	local orig_thresh2
+	local orig_thresh3
+
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	orig_thresh1=$(ip -j ntable show name "$tbl_name" | jq '.[] | select(has("thresh1")) | .["thresh1"]')
+	orig_thresh2=$(ip -j ntable show name "$tbl_name" | jq '.[] | select(has("thresh2")) | .["thresh2"]')
+	orig_thresh3=$(ip -j ntable show name "$tbl_name" | jq '.[] | select(has("thresh3")) | .["thresh3"]')
+	run_cmd "ip ntable change name $tbl_name thresh3 10 thresh2 9 thresh1 8"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh add ${subnet}3 lladdr $mac nud stale dev veth0"
+	run_cmd "sleep 5"
+	forced_gc_runs_t0=$(ip -j -s ntable show name "$tbl_name" | jq '.[] | select(has("forced_gc_runs")) | .["forced_gc_runs"]')
+	for i in {1..20}; do
+		run_cmd "ip -n $ns1 neigh add ${subnet}$((i + 4)) nud none dev veth0"
+	done
+	forced_gc_runs_t1=$(ip -j -s ntable show name "$tbl_name" | jq '.[] | select(has("forced_gc_runs")) | .["forced_gc_runs"]')
+	if [[ $forced_gc_runs_t1 -eq $forced_gc_runs_t0 ]]; then
+		check_err 1 "Forced garbage collection did not run"
+	fi
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_err $? "Entry with \"extern_valid\" flag did not survive forced garbage collection"
+	run_cmd "ip -n $ns1 neigh get ${subnet}3 dev veth0"
+	check_fail $? "Entry without \"extern_valid\" flag survived forced garbage collection"
+
+	log_test "$af_str \"extern_valid\" flag: Forced garbage collection"
+
+	run_cmd "ip ntable change name $tbl_name thresh3 $orig_thresh3 thresh2 $orig_thresh2 thresh1 $orig_thresh1"
+
+	RET=0
+
+	# Periodic garbage collection runs every "base_reachable"/2 seconds and
+	# if the number of entries is larger than "thresh1", then it deletes
+	# stale entries that have not been used in the last "gc_stale" seconds.
+	#
+	# Check that an "extern_valid" entry survives a periodic garbage
+	# collection. Add an "extern_valid" entry, add more than "thresh1"
+	# regular entries, wait "base_reachable" (longer than "gc_stale")
+	# seconds and check that the "extern_valid" entry was not deleted.
+	#
+	# Note that the garbage collection thresholds and "base_reachable" are
+	# global resources and that changes in the initial namespace affect all
+	# the namespaces.
+	local periodic_gc_runs_t0
+	local periodic_gc_runs_t1
+	local orig_base_reachable
+	local orig_gc_stale
+
+	run_cmd "ip -n $ns1 neigh flush dev veth0"
+	orig_thresh1=$(ip -j ntable show name "$tbl_name" | jq '.[] | select(has("thresh1")) | .["thresh1"]')
+	orig_base_reachable=$(ip -j ntable show name "$tbl_name" | jq '.[] | select(has("thresh1")) | .["base_reachable"]')
+	run_cmd "ip ntable change name $tbl_name thresh1 10 base_reachable 10000"
+	orig_gc_stale=$(ip -n "$ns1" -j ntable show name "$tbl_name" dev veth0 | jq '.[]["gc_stale"]')
+	run_cmd "ip -n $ns1 ntable change name $tbl_name dev veth0 gc_stale 5000"
+	# Wait orig_base_reachable/2 for the new interval to take effect.
+	run_cmd "sleep $(((orig_base_reachable / 1000) / 2 + 2))"
+	run_cmd "ip -n $ns1 neigh add $ip_addr lladdr $mac nud stale dev veth0 extern_valid"
+	run_cmd "ip -n $ns1 neigh add ${subnet}3 lladdr $mac nud stale dev veth0"
+	for i in {1..20}; do
+		run_cmd "ip -n $ns1 neigh add ${subnet}$((i + 4)) nud none dev veth0"
+	done
+	periodic_gc_runs_t0=$(ip -j -s ntable show name "$tbl_name" | jq '.[] | select(has("periodic_gc_runs")) | .["periodic_gc_runs"]')
+	run_cmd "sleep 10"
+	periodic_gc_runs_t1=$(ip -j -s ntable show name "$tbl_name" | jq '.[] | select(has("periodic_gc_runs")) | .["periodic_gc_runs"]')
+	[[ $periodic_gc_runs_t1 -ne $periodic_gc_runs_t0 ]]
+	check_err $? "Periodic garbage collection did not run"
+	run_cmd "ip -n $ns1 neigh get $ip_addr dev veth0 | grep \"extern_valid\""
+	check_err $? "Entry with \"extern_valid\" flag did not survive periodic garbage collection"
+	run_cmd "ip -n $ns1 neigh get ${subnet}3 dev veth0"
+	check_fail $? "Entry without \"extern_valid\" flag survived periodic garbage collection"
+
+	log_test "$af_str \"extern_valid\" flag: Periodic garbage collection"
+
+	run_cmd "ip -n $ns1 ntable change name $tbl_name dev veth0 gc_stale $orig_gc_stale"
+	run_cmd "ip ntable change name $tbl_name thresh1 $orig_thresh1 base_reachable $orig_base_reachable"
+}
+
+extern_valid_ipv4()
+{
+	extern_valid_common "IPv4" 192.0.2.2 "arp_cache" 192.0.2.
+}
+
+extern_valid_ipv6()
+{
+	extern_valid_common "IPv6" 2001:db8:1::2 "ndisc_cache" 2001:db8:1::
+}
+
+################################################################################
+# Usage
+
+usage()
+{
+	cat <<EOF
+usage: ${0##*/} OPTS
+
+        -t <test>   Test(s) to run (default: all)
+                    (options: $TESTS)
+        -p          Pause on fail
+        -v          Verbose mode (show commands and output)
+EOF
+}
+
+################################################################################
+# Main
+
+while getopts ":t:pvh" opt; do
+	case $opt in
+		t) TESTS=$OPTARG;;
+		p) PAUSE_ON_FAIL=yes;;
+		v) VERBOSE=$((VERBOSE + 1));;
+		h) usage; exit 0;;
+		*) usage; exit 1;;
+	esac
+done
+
+require_command jq
+
+if ! ip neigh help 2>&1 | grep -q "extern_valid"; then
+	echo "SKIP: iproute2 ip too old, missing \"extern_valid\" support"
+	exit "$ksft_skip"
+fi
+
+trap exit_cleanup_all EXIT
+
+for t in $TESTS
+do
+	setup; $t; cleanup_all_ns;
+done
-- 
2.49.0

Re: [PATCH net-next v2 2/2] selftests: net: Add a selftest for externally validated neighbor entries

[Jakub Kicinski]

On Thu, 26 Jun 2025 10:31:11 +0300 Ido Schimmel wrote:
> +TEST_PROGS += test_neigh.sh

Hi Ido!

This one is a bit flaky running on the normal/"non-debug" kernel:
https://netdev.bots.linux.dev/contest.html?executor=vmksft-net&test=test-neigh-sh
Looks like we get a flake for 1 in 10 runs :( Could you TAL?

Re: [PATCH net-next v2 2/2] selftests: net: Add a selftest for externally validated neighbor entries

[Ido Schimmel]

On Mon, Jul 28, 2025 at 09:35:04AM -0700, Jakub Kicinski wrote:
> On Thu, 26 Jun 2025 10:31:11 +0300 Ido Schimmel wrote:
> > +TEST_PROGS += test_neigh.sh
> 
> Hi Ido!
> 
> This one is a bit flaky running on the normal/"non-debug" kernel:
> https://netdev.bots.linux.dev/contest.html?executor=vmksft-net&test=test-neigh-sh
> Looks like we get a flake for 1 in 10 runs :( Could you TAL?

Yes, will check.

Thanks

Re: [PATCH net-next v2 0/2] Add support for externally validated neighbor entries

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 26 Jun 2025 10:31:09 +0300 you wrote:
> Patch #1 adds a new neighbor flag ("extern_valid") that prevents the
> kernel from invalidating or removing a neighbor entry, while allowing
> the kernel to notify user space when the entry becomes reachable. See
> motivation and implementation details in the commit message.
> 
> Patch #2 adds a selftest.
> 
> [...]

Here is the summary with links:
  - [net-next,v2,1/2] neighbor: Add NTF_EXT_VALIDATED flag for externally validated entries
    https://git.kernel.org/netdev/net-next/c/03dc03fa0432
  - [net-next,v2,2/2] selftests: net: Add a selftest for externally validated neighbor entries
    https://git.kernel.org/netdev/net-next/c/171f2ee31a42

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
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