diff --git a/include/crm/cluster.h b/include/crm/cluster.h
index 757bfcef50..0cd5487143 100644
--- a/include/crm/cluster.h
+++ b/include/crm/cluster.h
@@ -1,222 +1,229 @@
 /*
  * Copyright 2004-2021 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
  * This source code is licensed under the GNU Lesser General Public License
  * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
  */
 
 #ifndef PCMK__CRM_CLUSTER__H
 #  define PCMK__CRM_CLUSTER__H
 
 #  include <stdint.h>           // uint32_t, uint64_t
 #  include <glib.h>             // gboolean, GHashTable
 #  include <libxml/tree.h>      // xmlNode
 #  include <crm/common/xml.h>
 #  include <crm/common/util.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
 #  if SUPPORT_COROSYNC
 #    include <corosync/cpg.h>
 #  endif
 
 extern gboolean crm_have_quorum;
 extern GHashTable *crm_peer_cache;
 extern GHashTable *crm_remote_peer_cache;
 extern unsigned long long crm_peer_seq;
 
 #define CRM_NODE_LOST      "lost"
 #define CRM_NODE_MEMBER    "member"
 
 enum crm_join_phase {
+    /* @COMPAT: crm_join_nack_quiet can be replaced by a new
+     *          crm_node_t:feature_set at a compatibility break.
+     */
+    //! Not allowed to join, but don't send a nack message
+    crm_join_nack_quiet = -2,
+
     crm_join_nack       = -1,
     crm_join_none       = 0,
     crm_join_welcomed   = 1,
     crm_join_integrated = 2,
     crm_join_finalized  = 3,
     crm_join_confirmed  = 4,
 };
 
 enum crm_node_flags {
     /* node is not a cluster node and should not be considered for cluster membership */
     crm_remote_node          = 0x0001,
 
     /* node's cache entry is dirty */
     crm_node_dirty           = 0x0010,
 };
 
 typedef struct crm_peer_node_s {
     char *uname;                // Node name as known to cluster
     char *uuid;                 // Node UUID to ensure uniqueness
     char *state;                // @TODO change to enum
     uint64_t flags;             // Bitmask of crm_node_flags
     uint64_t last_seen;         // Only needed by cluster nodes
     uint32_t processes;         // @TODO most not needed, merge into flags
 
     /* @TODO When we can break public API compatibility, we can make the rest of
      * these members separate structs and use void *cluster_data and
      * void *user_data here instead, to abstract the cluster layer further.
      */
 
     // Currently only needed by corosync stack
     uint32_t id;                // Node ID
     time_t when_lost;           // When CPG membership was last lost
 
     // Only used by controller
     enum crm_join_phase join;
     char *expected;
 } crm_node_t;
 
 void crm_peer_init(void);
 void crm_peer_destroy(void);
 
 typedef struct crm_cluster_s {
     char *uuid;
     char *uname;
     uint32_t nodeid;
 
     void (*destroy) (gpointer);
 
 #  if SUPPORT_COROSYNC
     /* @TODO When we can break public API compatibility, make these members a
      * separate struct and use void *cluster_data here instead, to abstract the
      * cluster layer further.
      */
     struct cpg_name group;
     cpg_callbacks_t cpg;
     cpg_handle_t cpg_handle;
 #  endif
 
 } crm_cluster_t;
 
 gboolean crm_cluster_connect(crm_cluster_t *cluster);
 void crm_cluster_disconnect(crm_cluster_t *cluster);
 
 enum crm_ais_msg_class {
     crm_class_cluster = 0,
 };
 
 enum crm_ais_msg_types {
     crm_msg_none     = 0,
     crm_msg_ais      = 1,
     crm_msg_lrmd     = 2,
     crm_msg_cib      = 3,
     crm_msg_crmd     = 4,
     crm_msg_attrd    = 5,
     crm_msg_stonithd = 6,
     crm_msg_te       = 7,
     crm_msg_pe       = 8,
     crm_msg_stonith_ng = 9,
 };
 
 /* used with crm_get_peer_full */
 enum crm_get_peer_flags {
     CRM_GET_PEER_CLUSTER   = 0x0001,
     CRM_GET_PEER_REMOTE    = 0x0002,
     CRM_GET_PEER_ANY       = CRM_GET_PEER_CLUSTER|CRM_GET_PEER_REMOTE,
 };
 
 gboolean send_cluster_message(crm_node_t *node, enum crm_ais_msg_types service,
                               xmlNode *data, gboolean ordered);
 
 int crm_remote_peer_cache_size(void);
 
 /* Initialize and refresh the remote peer cache from a cib config */
 void crm_remote_peer_cache_refresh(xmlNode *cib);
 crm_node_t *crm_remote_peer_get(const char *node_name);
 void crm_remote_peer_cache_remove(const char *node_name);
 
 /* allows filtering of remote and cluster nodes using crm_get_peer_flags */
 crm_node_t *crm_get_peer_full(unsigned int id, const char *uname, int flags);
 
 /* only searches cluster nodes */
 crm_node_t *crm_get_peer(unsigned int id, const char *uname);
 
 guint crm_active_peers(void);
 gboolean crm_is_peer_active(const crm_node_t * node);
 guint reap_crm_member(uint32_t id, const char *name);
 
 #  if SUPPORT_COROSYNC
 uint32_t get_local_nodeid(cpg_handle_t handle);
 
 gboolean cluster_connect_cpg(crm_cluster_t *cluster);
 void cluster_disconnect_cpg(crm_cluster_t * cluster);
 
 void pcmk_cpg_membership(cpg_handle_t handle,
                          const struct cpg_name *groupName,
                          const struct cpg_address *member_list, size_t member_list_entries,
                          const struct cpg_address *left_list, size_t left_list_entries,
                          const struct cpg_address *joined_list, size_t joined_list_entries);
 gboolean crm_is_corosync_peer_active(const crm_node_t * node);
 gboolean send_cluster_text(enum crm_ais_msg_class msg_class, const char *data,
                            gboolean local, crm_node_t * node,
                            enum crm_ais_msg_types dest);
 char *pcmk_message_common_cs(cpg_handle_t handle, uint32_t nodeid, uint32_t pid, void *msg,
                         uint32_t *kind, const char **from);
 #  endif
 
 const char *crm_peer_uuid(crm_node_t *node);
 const char *crm_peer_uname(const char *uuid);
 void set_uuid(xmlNode *xml, const char *attr, crm_node_t *node);
 
 enum crm_status_type {
     crm_status_uname,
     crm_status_nstate,
     crm_status_processes,
 };
 
 enum crm_ais_msg_types text2msg_type(const char *text);
 void crm_set_status_callback(void (*dispatch) (enum crm_status_type, crm_node_t *, const void *));
 void crm_set_autoreap(gboolean autoreap);
 
 enum cluster_type_e {
     pcmk_cluster_unknown     = 0x0001,
     pcmk_cluster_invalid     = 0x0002,
     // 0x0004 was heartbeat
     // 0x0010 was corosync 1 with plugin
     pcmk_cluster_corosync    = 0x0020,
     // 0x0040 was corosync 1 with CMAN
 };
 
 enum cluster_type_e get_cluster_type(void);
 const char *name_for_cluster_type(enum cluster_type_e type);
 
 gboolean is_corosync_cluster(void);
 
 const char *get_local_node_name(void);
 char *get_node_name(uint32_t nodeid);
 
 /*!
  * \brief Get log-friendly string equivalent of a join phase
  *
  * \param[in] phase  Join phase
  *
  * \return Log-friendly string equivalent of \p phase
  */
 static inline const char *
 crm_join_phase_str(enum crm_join_phase phase)
 {
     switch (phase) {
+        case crm_join_nack_quiet:   return "nack_quiet";
         case crm_join_nack:         return "nack";
         case crm_join_none:         return "none";
         case crm_join_welcomed:     return "welcomed";
         case crm_join_integrated:   return "integrated";
         case crm_join_finalized:    return "finalized";
         case crm_join_confirmed:    return "confirmed";
+        default:                    return "invalid";
     }
-    return "invalid";
 }
 
 #if !defined(PCMK_ALLOW_DEPRECATED) || (PCMK_ALLOW_DEPRECATED == 1)
 #include <crm/cluster/compat.h>
 #endif
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif