Merge pull request #5901 from mjstapp/backup_nh_prep

zebra, lib: Backup nexthop (path) prep work

9 files changed, 281 insertions, 27 deletions

diff --git a/lib/ipaddr.h b/lib/ipaddr.h
index c6372f1abb..cd7f79a04e 100644
--- a/lib/ipaddr.h
+++ b/lib/ipaddr.h
@@ -112,7 +112,7 @@ static inline void ipv4_to_ipv4_mapped_ipv6(struct in6_addr *in6,
 /*
  * convert an ipv4 mapped ipv6 address back to ipv4 address
  */
-static inline void ipv4_mapped_ipv6_to_ipv4(struct in6_addr *in6,
+static inline void ipv4_mapped_ipv6_to_ipv4(const struct in6_addr *in6,
 					    struct in_addr *in)
 {
 	memset(in, 0, sizeof(struct in_addr));
diff --git a/lib/mpls.c b/lib/mpls.c
index 759fe1206d..ac5792a686 100644
--- a/lib/mpls.c
+++ b/lib/mpls.c
@@ -79,7 +79,7 @@ int mpls_str2label(const char *label_str, uint8_t *num_labels,
 /*
  * Label to string conversion, labels in string separated by '/'.
  */
-char *mpls_label2str(uint8_t num_labels, mpls_label_t *labels, char *buf,
+char *mpls_label2str(uint8_t num_labels, const mpls_label_t *labels, char *buf,
 		     int len, int pretty)
 {
 	char label_buf[BUFSIZ];
diff --git a/lib/mpls.h b/lib/mpls.h
index 635ecc77a1..05cf2935e8 100644
--- a/lib/mpls.h
+++ b/lib/mpls.h
@@ -209,10 +209,13 @@ static inline char *label2str(mpls_label_t label, char *buf, size_t len)
 int mpls_str2label(const char *label_str, uint8_t *num_labels,
 		   mpls_label_t *labels);
 
+/* Generic string buffer for label-stack-to-str */
+#define MPLS_LABEL_STRLEN 1024
+
 /*
  * Label to string conversion, labels in string separated by '/'.
  */
-char *mpls_label2str(uint8_t num_labels, mpls_label_t *labels, char *buf,
+char *mpls_label2str(uint8_t num_labels, const mpls_label_t *labels, char *buf,
 		     int len, int pretty);
 
 #ifdef __cplusplus
diff --git a/lib/nexthop.c b/lib/nexthop.c
index c3be0a71e6..0d239e091b 100644
--- a/lib/nexthop.c
+++ b/lib/nexthop.c
@@ -23,11 +23,9 @@
 #include "table.h"
 #include "memory.h"
 #include "command.h"
-#include "if.h"
 #include "log.h"
 #include "sockunion.h"
 #include "linklist.h"
-#include "thread.h"
 #include "prefix.h"
 #include "nexthop.h"
 #include "mpls.h"
@@ -155,7 +153,24 @@ static int _nexthop_cmp_no_labels(const struct nexthop *next1,
 	}
 
 	ret = _nexthop_source_cmp(next1, next2);
+	if (ret != 0)
+		goto done;
+
+	if (!CHECK_FLAG(next1->flags, NEXTHOP_FLAG_HAS_BACKUP) &&
+	    CHECK_FLAG(next2->flags, NEXTHOP_FLAG_HAS_BACKUP))
+		return -1;
+
+	if (CHECK_FLAG(next1->flags, NEXTHOP_FLAG_HAS_BACKUP) &&
+	    !CHECK_FLAG(next2->flags, NEXTHOP_FLAG_HAS_BACKUP))
+		return 1;
+
+	if (next1->backup_idx < next2->backup_idx)
+		return -1;
+
+	if (next1->backup_idx > next2->backup_idx)
+		return 1;
 
+done:
 	return ret;
 }
 
@@ -240,7 +255,7 @@ struct nexthop *nexthop_new(void)
 	 * The linux kernel does some weird stuff with adding +1 to
 	 * all nexthop weights it gets over netlink.
 	 * To handle this, just default everything to 1 right from
-	 * from the beggining so we don't have to special case
+	 * from the beginning so we don't have to special case
 	 * default weights in the linux netlink code.
 	 *
 	 * 1 should be a valid on all platforms anyway.
@@ -393,8 +408,8 @@ struct nexthop *nexthop_from_blackhole(enum blackhole_type bh_type)
 }
 
 /* Update nexthop with label information. */
-void nexthop_add_labels(struct nexthop *nexthop, enum lsp_types_t type,
-			uint8_t num_labels, mpls_label_t *label)
+void nexthop_add_labels(struct nexthop *nexthop, enum lsp_types_t ltype,
+			uint8_t num_labels, const mpls_label_t *labels)
 {
 	struct mpls_label_stack *nh_label;
 	int i;
@@ -402,13 +417,18 @@ void nexthop_add_labels(struct nexthop *nexthop, enum lsp_types_t type,
 	if (num_labels == 0)
 		return;
 
-	nexthop->nh_label_type = type;
+	/* Enforce limit on label stack size */
+	if (num_labels > MPLS_MAX_LABELS)
+		num_labels = MPLS_MAX_LABELS;
+
+	nexthop->nh_label_type = ltype;
+
 	nh_label = XCALLOC(MTYPE_NH_LABEL,
 			   sizeof(struct mpls_label_stack)
 				   + num_labels * sizeof(mpls_label_t));
 	nh_label->num_labels = num_labels;
 	for (i = 0; i < num_labels; i++)
-		nh_label->label[i] = *(label + i);
+		nh_label->label[i] = *(labels + i);
 	nexthop->nh_label = nh_label;
 }
 
@@ -503,6 +523,7 @@ unsigned int nexthop_level(struct nexthop *nexthop)
 uint32_t nexthop_hash_quick(const struct nexthop *nexthop)
 {
 	uint32_t key = 0x45afe398;
+	uint32_t val;
 
 	key = jhash_3words(nexthop->type, nexthop->vrf_id,
 			   nexthop->nh_label_type, key);
@@ -532,8 +553,12 @@ uint32_t nexthop_hash_quick(const struct nexthop *nexthop)
 			key = jhash_1word(nexthop->nh_label->label[i], key);
 	}
 
-	key = jhash_2words(nexthop->ifindex,
-			   CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_ONLINK),
+	val = 0;
+	if (CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_HAS_BACKUP))
+		val = (uint32_t)nexthop->backup_idx;
+
+	key = jhash_3words(nexthop->ifindex,
+			   CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_ONLINK), val,
 			   key);
 
 	return key;
@@ -573,6 +598,7 @@ void nexthop_copy_no_recurse(struct nexthop *copy,
 	copy->type = nexthop->type;
 	copy->flags = nexthop->flags;
 	copy->weight = nexthop->weight;
+	copy->backup_idx = nexthop->backup_idx;
 	memcpy(&copy->gate, &nexthop->gate, sizeof(nexthop->gate));
 	memcpy(&copy->src, &nexthop->src, sizeof(nexthop->src));
 	memcpy(&copy->rmap_src, &nexthop->rmap_src, sizeof(nexthop->rmap_src));
diff --git a/lib/nexthop.h b/lib/nexthop.h
index 267f9f28ad..c4e88dd844 100644
--- a/lib/nexthop.h
+++ b/lib/nexthop.h
@@ -86,6 +86,8 @@ struct nexthop {
 					  * active one
 					  */
 #define NEXTHOP_FLAG_RNH_FILTERED  (1 << 5) /* rmap filtered, used by rnh */
+#define NEXTHOP_FLAG_HAS_BACKUP (1 << 6)    /* Backup nexthop index is set */
+
 #define NEXTHOP_IS_ACTIVE(flags)                                               \
 	(CHECK_FLAG(flags, NEXTHOP_FLAG_ACTIVE)                                \
 	 && !CHECK_FLAG(flags, NEXTHOP_FLAG_DUPLICATE))
@@ -116,15 +118,31 @@ struct nexthop {
 
 	/* Weight of the nexthop ( for unequal cost ECMP ) */
 	uint8_t weight;
+
+	/* Index of a corresponding backup nexthop in a backup list;
+	 * only meaningful if the HAS_BACKUP flag is set.
+	 */
+	uint8_t backup_idx;
 };
 
+/* Backup index value is limited */
+#define NEXTHOP_BACKUP_IDX_MAX 255
+
+/* Utility to append one nexthop to another. */
+#define NEXTHOP_APPEND(to, new)           \
+	do {                              \
+		(to)->next = (new);       \
+		(new)->prev = (to);       \
+		(new)->next = NULL;       \
+	} while (0)
+
 struct nexthop *nexthop_new(void);
 
 void nexthop_free(struct nexthop *nexthop);
 void nexthops_free(struct nexthop *nexthop);
 
-void nexthop_add_labels(struct nexthop *, enum lsp_types_t, uint8_t,
-			mpls_label_t *);
+void nexthop_add_labels(struct nexthop *nexthop, enum lsp_types_t ltype,
+			uint8_t num_labels, const mpls_label_t *labels);
 void nexthop_del_labels(struct nexthop *);
 
 /*
diff --git a/lib/nexthop_group.c b/lib/nexthop_group.c
index d660428bcd..8c3bbbdcd4 100644
--- a/lib/nexthop_group.c
+++ b/lib/nexthop_group.c
@@ -43,8 +43,12 @@ struct nexthop_hold {
 	char *intf;
 	char *labels;
 	uint32_t weight;
+	int backup_idx; /* Index of backup nexthop, if >= 0 */
 };
 
+/* Invalid/unset value for nexthop_hold's backup_idx */
+#define NHH_BACKUP_IDX_INVALID -1
+
 struct nexthop_group_hooks {
 	void (*new)(const char *name);
 	void (*add_nexthop)(const struct nexthop_group_cmd *nhg,
@@ -225,6 +229,10 @@ void nexthop_group_copy(struct nexthop_group *to,
 
 void nexthop_group_delete(struct nexthop_group **nhg)
 {
+	/* OK to call with NULL group */
+	if ((*nhg) == NULL)
+		return;
+
 	if ((*nhg)->nexthop)
 		nexthops_free((*nhg)->nexthop);
 
@@ -567,11 +575,36 @@ DEFUN_NOSH(no_nexthop_group, no_nexthop_group_cmd, "no nexthop-group NHGNAME",
 	return CMD_SUCCESS;
 }
 
+DEFPY(nexthop_group_backup, nexthop_group_backup_cmd,
+      "backup-group WORD$name",
+      "Specify a group name containing backup nexthops\n"
+      "The name of the backup group\n")
+{
+	VTY_DECLVAR_CONTEXT(nexthop_group_cmd, nhgc);
+
+	strlcpy(nhgc->backup_list_name, name, sizeof(nhgc->backup_list_name));
+
+	return CMD_SUCCESS;
+}
+
+DEFPY(no_nexthop_group_backup, no_nexthop_group_backup_cmd,
+      "no backup-group [WORD$name]",
+      NO_STR
+      "Clear group name containing backup nexthops\n"
+      "The name of the backup group\n")
+{
+	VTY_DECLVAR_CONTEXT(nexthop_group_cmd, nhgc);
+
+	nhgc->backup_list_name[0] = 0;
+
+	return CMD_SUCCESS;
+}
+
 static void nexthop_group_save_nhop(struct nexthop_group_cmd *nhgc,
 				    const char *nhvrf_name,
 				    const union sockunion *addr,
 				    const char *intf, const char *labels,
-				    const uint32_t weight)
+				    const uint32_t weight, int backup_idx)
 {
 	struct nexthop_hold *nh;
 
@@ -588,6 +621,8 @@ static void nexthop_group_save_nhop(struct nexthop_group_cmd *nhgc,
 
 	nh->weight = weight;
 
+	nh->backup_idx = backup_idx;
+
 	listnode_add_sort(nhgc->nhg_list, nh);
 }
 
@@ -629,7 +664,7 @@ static bool nexthop_group_parse_nexthop(struct nexthop *nhop,
 					const union sockunion *addr,
 					const char *intf, const char *name,
 					const char *labels, int *lbl_ret,
-					uint32_t weight)
+					uint32_t weight, int backup_idx)
 {
 	int ret = 0;
 	struct vrf *vrf;
@@ -688,6 +723,15 @@ static bool nexthop_group_parse_nexthop(struct nexthop *nhop,
 
 	nhop->weight = weight;
 
+	if (backup_idx != NHH_BACKUP_IDX_INVALID) {
+		/* Validate index value */
+		if (backup_idx > NEXTHOP_BACKUP_IDX_MAX)
+			return false;
+
+		SET_FLAG(nhop->flags, NEXTHOP_FLAG_HAS_BACKUP);
+		nhop->backup_idx = backup_idx;
+	}
+
 	return true;
 }
 
@@ -699,7 +743,7 @@ static bool nexthop_group_parse_nhh(struct nexthop *nhop,
 {
 	return (nexthop_group_parse_nexthop(nhop, nhh->addr, nhh->intf,
 					    nhh->nhvrf_name, nhh->labels, NULL,
-					    nhh->weight));
+					    nhh->weight, nhh->backup_idx));
 }
 
 DEFPY(ecmp_nexthops, ecmp_nexthops_cmd,
@@ -712,6 +756,7 @@ DEFPY(ecmp_nexthops, ecmp_nexthops_cmd,
 	   nexthop-vrf NAME$vrf_name \
 	   |label WORD \
            |weight (1-255) \
+           |backup-idx$bi_str (0-254)$idx \
 	}]",
       NO_STR
       "Specify one of the nexthops in this ECMP group\n"
@@ -724,16 +769,23 @@ DEFPY(ecmp_nexthops, ecmp_nexthops_cmd,
       "Specify label(s) for this nexthop\n"
       "One or more labels in the range (16-1048575) separated by '/'\n"
       "Weight to be used by the nexthop for purposes of ECMP\n"
-      "Weight value to be used\n")
+      "Weight value to be used\n"
+      "Backup nexthop index in another group\n"
+      "Nexthop index value\n")
 {
 	VTY_DECLVAR_CONTEXT(nexthop_group_cmd, nhgc);
 	struct nexthop nhop;
 	struct nexthop *nh;
 	int lbl_ret = 0;
 	bool legal;
+	int backup_idx = idx;
+	bool add_update = false;
+
+	if (bi_str == NULL)
+		backup_idx = NHH_BACKUP_IDX_INVALID;
 
 	legal = nexthop_group_parse_nexthop(&nhop, addr, intf, vrf_name, label,
-					    &lbl_ret, weight);
+					    &lbl_ret, weight, backup_idx);
 
 	if (nhop.type == NEXTHOP_TYPE_IPV6
 	    && IN6_IS_ADDR_LINKLOCAL(&nhop.gate.ipv6)) {
@@ -765,19 +817,30 @@ DEFPY(ecmp_nexthops, ecmp_nexthops_cmd,
 
 	nh = nexthop_exists(&nhgc->nhg, &nhop);
 
-	if (no) {
+	if (no || nh) {
+		/* Remove or replace cases */
+
+		/* Remove existing config */
 		nexthop_group_unsave_nhop(nhgc, vrf_name, addr, intf, label,
 					  weight);
 		if (nh) {
+			/* Remove nexthop object */
 			_nexthop_del(&nhgc->nhg, nh);
 
 			if (nhg_hooks.del_nexthop)
 				nhg_hooks.del_nexthop(nhgc, nh);
 
 			nexthop_free(nh);
+			nh = NULL;
 		}
-	} else if (!nh) {
-		/* must be adding new nexthop since !no and !nexthop_exists */
+	}
+
+	add_update = !no;
+
+	if (add_update) {
+		/* Add or replace cases */
+
+		/* If valid config, add nexthop object */
 		if (legal) {
 			nh = nexthop_new();
 
@@ -785,8 +848,9 @@ DEFPY(ecmp_nexthops, ecmp_nexthops_cmd,
 			_nexthop_add(&nhgc->nhg.nexthop, nh);
 		}
 
+		/* Save config always */
 		nexthop_group_save_nhop(nhgc, vrf_name, addr, intf, label,
-					weight);
+					weight, backup_idx);
 
 		if (legal && nhg_hooks.add_nexthop)
 			nhg_hooks.add_nexthop(nhgc, nh);
@@ -849,6 +913,9 @@ void nexthop_group_write_nexthop(struct vty *vty, struct nexthop *nh)
 	if (nh->weight)
 		vty_out(vty, " weight %u", nh->weight);
 
+	if (CHECK_FLAG(nh->flags, NEXTHOP_FLAG_HAS_BACKUP))
+		vty_out(vty, " backup-idx %d", nh->backup_idx);
+
 	vty_out(vty, "\n");
 }
 
@@ -874,6 +941,9 @@ static void nexthop_group_write_nexthop_internal(struct vty *vty,
 	if (nh->weight)
 		vty_out(vty, " weight %u", nh->weight);
 
+	if (nh->backup_idx != NHH_BACKUP_IDX_INVALID)
+		vty_out(vty, " backup-idx %d", nh->backup_idx);
+
 	vty_out(vty, "\n");
 }
 
@@ -887,6 +957,10 @@ static int nexthop_group_write(struct vty *vty)
 
 		vty_out(vty, "nexthop-group %s\n", nhgc->name);
 
+		if (nhgc->backup_list_name[0])
+			vty_out(vty, " backup-group %s\n",
+				nhgc->backup_list_name);
+
 		for (ALL_LIST_ELEMENTS_RO(nhgc->nhg_list, node, nh)) {
 			vty_out(vty, " ");
 			nexthop_group_write_nexthop_internal(vty, nh);
@@ -1067,6 +1141,8 @@ void nexthop_group_init(void (*new)(const char *name),
 	install_element(CONFIG_NODE, &no_nexthop_group_cmd);
 
 	install_default(NH_GROUP_NODE);
+	install_element(NH_GROUP_NODE, &nexthop_group_backup_cmd);
+	install_element(NH_GROUP_NODE, &no_nexthop_group_backup_cmd);
 	install_element(NH_GROUP_NODE, &ecmp_nexthops_cmd);
 
 	memset(&nhg_hooks, 0, sizeof(nhg_hooks));
diff --git a/lib/nexthop_group.h b/lib/nexthop_group.h
index f99a53f694..3a5a1299c1 100644
--- a/lib/nexthop_group.h
+++ b/lib/nexthop_group.h
@@ -57,6 +57,8 @@ void copy_nexthops(struct nexthop **tnh, const struct nexthop *nh,
 uint32_t nexthop_group_hash_no_recurse(const struct nexthop_group *nhg);
 uint32_t nexthop_group_hash(const struct nexthop_group *nhg);
 void nexthop_group_mark_duplicates(struct nexthop_group *nhg);
+
+/* Add a nexthop to a list, enforcing the canonical sort order. */
 void nexthop_group_add_sorted(struct nexthop_group *nhg,
 			      struct nexthop *nexthop);
 
@@ -79,11 +81,16 @@ void nexthop_group_add_sorted(struct nexthop_group *nhg,
 	(nhop) = nexthop_next(nhop)
 
 
+#define NHGC_NAME_SIZE 80
+
 struct nexthop_group_cmd {
 
 	RB_ENTRY(nexthop_group_cmd) nhgc_entry;
 
-	char name[80];
+	char name[NHGC_NAME_SIZE];
+
+	/* Name of group containing backup nexthops (if set) */
+	char backup_list_name[NHGC_NAME_SIZE];
 
 	struct nexthop_group nhg;
 
diff --git a/lib/zclient.c b/lib/zclient.c
index 1ac0e49e13..d380267a70 100644
--- a/lib/zclient.c
+++ b/lib/zclient.c
@@ -904,6 +904,7 @@ int zapi_nexthop_encode(struct stream *s, const struct zapi_nexthop *api_nh,
 		}
 	}
 
+	/* If present, set 'weight' flag before encoding flags */
 	if (api_nh->weight)
 		SET_FLAG(nh_flags, ZAPI_NEXTHOP_FLAG_WEIGHT);
 
@@ -948,6 +949,10 @@ int zapi_nexthop_encode(struct stream *s, const struct zapi_nexthop *api_nh,
 		stream_put(s, &(api_nh->rmac),
 			   sizeof(struct ethaddr));
 
+	/* Index of backup nexthop */
+	if (CHECK_FLAG(nh_flags, ZAPI_NEXTHOP_FLAG_HAS_BACKUP))
+		stream_putc(s, api_nh->backup_idx);
+
 done:
 	return ret;
 }
@@ -1007,6 +1012,10 @@ int zapi_route_encode(uint8_t cmd, struct stream *s, struct zapi_route *api)
 			return -1;
 		}
 
+		/* We canonicalize the nexthops by sorting them; this allows
+		 * zebra to resolve the list of nexthops to a nexthop-group
+		 * more efficiently.
+		 */
 		zapi_nexthop_group_sort(api->nexthops, api->nexthop_num);
 
 		stream_putw(s, api->nexthop_num);
@@ -1033,6 +1042,50 @@ int zapi_route_encode(uint8_t cmd, struct stream *s, struct zapi_route *api)
 		}
 	}
 
+	/* Backup nexthops  */
+	if (CHECK_FLAG(api->message, ZAPI_MESSAGE_BACKUP_NEXTHOPS)) {
+		/* limit the number of nexthops if necessary */
+		if (api->backup_nexthop_num > MULTIPATH_NUM) {
+			char buf[PREFIX2STR_BUFFER];
+
+			prefix2str(&api->prefix, buf, sizeof(buf));
+			flog_err(
+				EC_LIB_ZAPI_ENCODE,
+				"%s: prefix %s: can't encode %u backup nexthops (maximum is %u)",
+				__func__, buf, api->backup_nexthop_num,
+				MULTIPATH_NUM);
+			return -1;
+		}
+
+		/* Note that we do not sort the list of backup nexthops -
+		 * this list is treated as an array and indexed by each
+		 * primary nexthop that is associated with a backup.
+		 */
+
+		stream_putw(s, api->backup_nexthop_num);
+
+		for (i = 0; i < api->backup_nexthop_num; i++) {
+			api_nh = &api->backup_nexthops[i];
+
+			/* MPLS labels for BGP-LU or Segment Routing */
+			if (api_nh->label_num > MPLS_MAX_LABELS) {
+				char buf[PREFIX2STR_BUFFER];
+
+				prefix2str(&api->prefix, buf, sizeof(buf));
+
+				flog_err(EC_LIB_ZAPI_ENCODE,
+					 "%s: prefix %s: backup: can't encode %u labels (maximum is %u)",
+					 __func__, buf,
+					 api_nh->label_num,
+					 MPLS_MAX_LABELS);
+				return -1;
+			}
+
+			if (zapi_nexthop_encode(s, api_nh, api->flags) != 0)
+				return -1;
+		}
+	}
+
 	/* Attributes. */
 	if (CHECK_FLAG(api->message, ZAPI_MESSAGE_DISTANCE))
 		stream_putc(s, api->distance);
@@ -1108,6 +1161,10 @@ static int zapi_nexthop_decode(struct stream *s, struct zapi_nexthop *api_nh,
 		STREAM_GET(&(api_nh->rmac), s,
 			   sizeof(struct ethaddr));
 
+	/* Backup nexthop index */
+	if (CHECK_FLAG(api_nh->flags, ZAPI_NEXTHOP_FLAG_HAS_BACKUP))
+		STREAM_GETC(s, api_nh->backup_idx);
+
 	/* Success */
 	ret = 0;
 
@@ -1214,6 +1271,24 @@ int zapi_route_decode(struct stream *s, struct zapi_route *api)
 		}
 	}
 
+	/* Backup nexthops. */
+	if (CHECK_FLAG(api->message, ZAPI_MESSAGE_BACKUP_NEXTHOPS)) {
+		STREAM_GETW(s, api->backup_nexthop_num);
+		if (api->backup_nexthop_num > MULTIPATH_NUM) {
+			flog_err(EC_LIB_ZAPI_ENCODE,
+				 "%s: invalid number of backup nexthops (%u)",
+				 __func__, api->backup_nexthop_num);
+			return -1;
+		}
+
+		for (i = 0; i < api->backup_nexthop_num; i++) {
+			api_nh = &api->backup_nexthops[i];
+
+			if (zapi_nexthop_decode(s, api_nh, api->flags) != 0)
+				return -1;
+		}
+	}
+
 	/* Attributes. */
 	if (CHECK_FLAG(api->message, ZAPI_MESSAGE_DISTANCE))
 		STREAM_GETC(s, api->distance);
@@ -1388,7 +1463,7 @@ stream_failure:
 	return false;
 }
 
-struct nexthop *nexthop_from_zapi_nexthop(struct zapi_nexthop *znh)
+struct nexthop *nexthop_from_zapi_nexthop(const struct zapi_nexthop *znh)
 {
 	struct nexthop *n = nexthop_new();
 
@@ -1405,6 +1480,11 @@ struct nexthop *nexthop_from_zapi_nexthop(struct zapi_nexthop *znh)
 				   znh->labels);
 	}
 
+	if (CHECK_FLAG(znh->flags, ZAPI_NEXTHOP_FLAG_HAS_BACKUP)) {
+		SET_FLAG(n->flags, NEXTHOP_FLAG_HAS_BACKUP);
+		n->backup_idx = znh->backup_idx;
+	}
+
 	return n;
 }
 
@@ -1420,10 +1500,16 @@ int zapi_nexthop_from_nexthop(struct zapi_nexthop *znh,
 
 	znh->type = nh->type;
 	znh->vrf_id = nh->vrf_id;
+	znh->weight = nh->weight;
 	znh->ifindex = nh->ifindex;
 	znh->gate = nh->gate;
 
 	if (nh->nh_label && (nh->nh_label->num_labels > 0)) {
+
+		/* Validate */
+		if (nh->nh_label->num_labels > MPLS_MAX_LABELS)
+			return -1;
+
 		for (i = 0; i < nh->nh_label->num_labels; i++)
 			znh->labels[i] = nh->nh_label->label[i];
 
@@ -1431,10 +1517,31 @@ int zapi_nexthop_from_nexthop(struct zapi_nexthop *znh,
 		SET_FLAG(znh->flags, ZAPI_NEXTHOP_FLAG_LABEL);
 	}
 
+	if (CHECK_FLAG(nh->flags, NEXTHOP_FLAG_HAS_BACKUP)) {
+		SET_FLAG(znh->flags, ZAPI_NEXTHOP_FLAG_HAS_BACKUP);
+		znh->backup_idx = nh->backup_idx;
+	}
+
 	return 0;
 }
 
 /*
+ * Wrapper that converts backup nexthop
+ */
+int zapi_backup_nexthop_from_nexthop(struct zapi_nexthop *znh,
+				     const struct nexthop *nh)
+{
+	int ret;
+
+	/* Ensure that zapi flags are correct: backups don't have backups */
+	ret = zapi_nexthop_from_nexthop(znh, nh);
+	if (ret == 0)
+		UNSET_FLAG(znh->flags, ZAPI_NEXTHOP_FLAG_HAS_BACKUP);
+
+	return ret;
+}
+
+/*
  * Decode the nexthop-tracking update message
  */
 bool zapi_nexthop_update_decode(struct stream *s, struct zapi_route *nhr)
diff --git a/lib/zclient.h b/lib/zclient.h
index 4de42a35bb..e747809f16 100644
--- a/lib/zclient.h
+++ b/lib/zclient.h
@@ -341,6 +341,9 @@ struct zclient {
 #define ZAPI_MESSAGE_TAG      0x08
 #define ZAPI_MESSAGE_MTU      0x10
 #define ZAPI_MESSAGE_SRCPFX   0x20
+/* Backup nexthops are present */
+#define ZAPI_MESSAGE_BACKUP_NEXTHOPS 0x40
+
 /*
  * This should only be used by a DAEMON that needs to communicate
  * the table being used is not in the VRF.  You must pass the
@@ -377,14 +380,21 @@ struct zapi_nexthop {
 	struct ethaddr rmac;
 
 	uint32_t weight;
+
+	/* Index of backup nexthop */
+	uint8_t backup_idx;
 };
 
 /*
- * ZAPI nexthop flags values
+ * ZAPI nexthop flags values - we're encoding a single octet
+ * initially, so ensure that the on-the-wire encoding continues
+ * to match the number of valid flags.
  */
+
 #define ZAPI_NEXTHOP_FLAG_ONLINK	0x01
 #define ZAPI_NEXTHOP_FLAG_LABEL		0x02
 #define ZAPI_NEXTHOP_FLAG_WEIGHT	0x04
+#define ZAPI_NEXTHOP_FLAG_HAS_BACKUP	0x08 /* Nexthop has a backup */
 
 /*
  * Some of these data structures do not map easily to
@@ -448,6 +458,10 @@ struct zapi_route {
 	uint16_t nexthop_num;
 	struct zapi_nexthop nexthops[MULTIPATH_NUM];
 
+	/* Support backup routes for IP FRR, TI-LFA, traffic engineering */
+	uint16_t backup_nexthop_num;
+	struct zapi_nexthop backup_nexthops[MULTIPATH_NUM];
+
 	uint8_t distance;
 
 	uint32_t metric;
@@ -769,9 +783,12 @@ bool zapi_iptable_notify_decode(struct stream *s,
 		uint32_t *unique,
 		enum zapi_iptable_notify_owner *note);
 
-extern struct nexthop *nexthop_from_zapi_nexthop(struct zapi_nexthop *znh);
+extern struct nexthop *
+nexthop_from_zapi_nexthop(const struct zapi_nexthop *znh);
 int zapi_nexthop_from_nexthop(struct zapi_nexthop *znh,
 			      const struct nexthop *nh);
+int zapi_backup_nexthop_from_nexthop(struct zapi_nexthop *znh,
+				     const struct nexthop *nh);
 extern bool zapi_nexthop_update_decode(struct stream *s,
 				       struct zapi_route *nhr);