diff --git a/src/libsystemd/sd-json/json-util.c b/src/libsystemd/sd-json/json-util.c
index a1b2ebc0fe..db7a2ac1e8 100644
--- a/src/libsystemd/sd-json/json-util.c
+++ b/src/libsystemd/sd-json/json-util.c
@@ -306,6 +306,26 @@ int json_dispatch_pidref(const char *name, sd_json_variant *variant, sd_json_dis
         return 0;
 }
 
+int json_dispatch_ifindex(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
+        int *ifi = ASSERT_PTR(userdata), r, t;
+
+        if (sd_json_variant_is_null(variant)) {
+                *ifi = 0;
+                return 0;
+        }
+
+        r = sd_json_dispatch_int(name, variant, flags, &t);
+        if (r < 0)
+                return r;
+
+        /* If SD_JSON_RELAX is set allow a zero interface index, otherwise refuse. */
+        if (t < (FLAGS_SET(flags, SD_JSON_RELAX) ? 0 : 1))
+                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is out of bounds for an interface index.", strna(name));
+
+        *ifi = t;
+        return 0;
+}
+
 int json_variant_new_devnum(sd_json_variant **ret, dev_t devnum) {
         if (devnum == 0)
                 return sd_json_variant_new_null(ret);
diff --git a/src/libsystemd/sd-json/json-util.h b/src/libsystemd/sd-json/json-util.h
index 81c0fd02a6..b824fa8a81 100644
--- a/src/libsystemd/sd-json/json-util.h
+++ b/src/libsystemd/sd-json/json-util.h
@@ -115,6 +115,7 @@ int json_dispatch_in_addr(const char *name, sd_json_variant *variant, sd_json_di
 int json_dispatch_path(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_pidref(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 int json_dispatch_devnum(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
+int json_dispatch_ifindex(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata);
 
 static inline int json_variant_unbase64_iovec(sd_json_variant *v, struct iovec *ret) {
         return sd_json_variant_unbase64(v, ret ? &ret->iov_base : NULL, ret ? &ret->iov_len : NULL);
diff --git a/src/network/networkctl-lldp.c b/src/network/networkctl-lldp.c
index 8a10562b0d..43ffbabb9f 100644
--- a/src/network/networkctl-lldp.c
+++ b/src/network/networkctl-lldp.c
@@ -27,10 +27,10 @@ static void interface_info_done(InterfaceInfo *p) {
 }
 
 static const sd_json_dispatch_field interface_info_dispatch_table[] = {
-        { "InterfaceIndex",            _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,          offsetof(InterfaceInfo, ifindex),  SD_JSON_MANDATORY },
-        { "InterfaceName",             SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(InterfaceInfo, ifname),   SD_JSON_MANDATORY },
-        { "InterfaceAlternativeNames", SD_JSON_VARIANT_ARRAY,         sd_json_dispatch_strv,         offsetof(InterfaceInfo, altnames), 0                 },
-        { "Neighbors",                 SD_JSON_VARIANT_ARRAY,         sd_json_dispatch_variant,      offsetof(InterfaceInfo, v),        0                 },
+        { "InterfaceIndex",            _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,         offsetof(InterfaceInfo, ifindex),  SD_JSON_MANDATORY|SD_JSON_RELAX },
+        { "InterfaceName",             SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(InterfaceInfo, ifname),   SD_JSON_MANDATORY               },
+        { "InterfaceAlternativeNames", SD_JSON_VARIANT_ARRAY,         sd_json_dispatch_strv,         offsetof(InterfaceInfo, altnames), 0                               },
+        { "Neighbors",                 SD_JSON_VARIANT_ARRAY,         sd_json_dispatch_variant,      offsetof(InterfaceInfo, v),        0                               },
         {},
 };
 
diff --git a/src/network/networkd-manager-varlink.c b/src/network/networkd-manager-varlink.c
index ce986e2cdc..9fe8e60769 100644
--- a/src/network/networkd-manager-varlink.c
+++ b/src/network/networkd-manager-varlink.c
@@ -69,8 +69,8 @@ typedef struct InterfaceInfo {
 
 static int dispatch_interface(sd_varlink *vlink, sd_json_variant *parameters, Manager *manager, Link **ret) {
         static const sd_json_dispatch_field dispatch_table[] = {
-                { "InterfaceIndex", _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,          offsetof(InterfaceInfo, ifindex), 0 },
-                { "InterfaceName",  SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(InterfaceInfo, ifname),  0 },
+                { "InterfaceIndex", _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,         offsetof(InterfaceInfo, ifindex), SD_JSON_RELAX },
+                { "InterfaceName",  SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(InterfaceInfo, ifname),  0             },
                 {}
         };
 
diff --git a/src/nss-resolve/nss-resolve.c b/src/nss-resolve/nss-resolve.c
index 91c5f11cb2..1c64ac2fd0 100644
--- a/src/nss-resolve/nss-resolve.c
+++ b/src/nss-resolve/nss-resolve.c
@@ -96,23 +96,6 @@ static uint32_t ifindex_to_scopeid(int family, const void *a, int ifindex) {
         return in6_addr_is_link_local(&in6) ? ifindex : 0;
 }
 
-static int json_dispatch_ifindex(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
-        int *ifi = ASSERT_PTR(userdata);
-        int64_t t;
-
-        assert(variant);
-
-        if (!sd_json_variant_is_integer(variant))
-                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is not an integer.", strna(name));
-
-        t = sd_json_variant_integer(variant);
-        if (t > INT_MAX)
-                return json_log(variant, flags, SYNTHETIC_ERRNO(EINVAL), "JSON field '%s' is out of bounds for an interface index.", strna(name));
-
-        *ifi = (int) t;
-        return 0;
-}
-
 static int json_dispatch_family(const char *name, sd_json_variant *variant, sd_json_dispatch_flags_t flags, void *userdata) {
         int *family = ASSERT_PTR(userdata);
         int64_t t;
diff --git a/src/resolve/resolvectl.c b/src/resolve/resolvectl.c
index 62354b4784..0dd2ca5fc7 100644
--- a/src/resolve/resolvectl.c
+++ b/src/resolve/resolvectl.c
@@ -3114,7 +3114,7 @@ static int dump_cache_scope(sd_json_variant *scope) {
         static const sd_json_dispatch_field dispatch_table[] = {
                 { "protocol", SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct scope_info, protocol), SD_JSON_MANDATORY },
                 { "family",   _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,           offsetof(struct scope_info, family),   0                 },
-                { "ifindex",  _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,           offsetof(struct scope_info, ifindex),  0                 },
+                { "ifindex",  _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,          offsetof(struct scope_info, ifindex),  SD_JSON_RELAX     },
                 { "ifname",   SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct scope_info, ifname),   0                 },
                 { "cache",    SD_JSON_VARIANT_ARRAY,         sd_json_dispatch_variant_noref, offsetof(struct scope_info, cache),    SD_JSON_MANDATORY },
                 {},
@@ -3226,7 +3226,7 @@ static int dump_server_state(sd_json_variant *server) {
                 { "Server",                 SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct server_state, server_name),               SD_JSON_MANDATORY },
                 { "Type",                   SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct server_state, type),                      SD_JSON_MANDATORY },
                 { "Interface",              SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct server_state, ifname),                    0                 },
-                { "InterfaceIndex",         _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,           offsetof(struct server_state, ifindex),                   0                 },
+                { "InterfaceIndex",         _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,          offsetof(struct server_state, ifindex),                   SD_JSON_RELAX     },
                 { "VerifiedFeatureLevel",   SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct server_state, verified_feature_level),    0                 },
                 { "PossibleFeatureLevel",   SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct server_state, possible_feature_level),    0                 },
                 { "DNSSECMode",             SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string,  offsetof(struct server_state, dnssec_mode),               SD_JSON_MANDATORY },
diff --git a/src/resolve/resolved-varlink.c b/src/resolve/resolved-varlink.c
index 168923e6b5..456347fd7e 100644
--- a/src/resolve/resolved-varlink.c
+++ b/src/resolve/resolved-varlink.c
@@ -321,7 +321,7 @@ static int parse_as_address(sd_varlink *link, LookupParameters *p) {
 
 static int vl_method_resolve_hostname(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
         static const sd_json_dispatch_field dispatch_table[] = {
-                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,    offsetof(LookupParameters, ifindex), 0                 },
+                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,   offsetof(LookupParameters, ifindex), SD_JSON_RELAX     },
                 { "name",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_string, offsetof(LookupParameters, name),    SD_JSON_MANDATORY },
                 { "family",  _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,    offsetof(LookupParameters, family),  0                 },
                 { "flags",   _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint64, offsetof(LookupParameters, flags),   0                 },
@@ -348,9 +348,6 @@ static int vl_method_resolve_hostname(sd_varlink *link, sd_json_variant *paramet
         if (r != 0)
                 return r;
 
-        if (p.ifindex < 0)
-                return sd_varlink_error_invalid_parameter(link, JSON_VARIANT_STRING_CONST("ifindex"));
-
         r = dns_name_is_valid(p.name);
         if (r < 0)
                 return r;
@@ -490,7 +487,7 @@ finish:
 
 static int vl_method_resolve_address(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
         static const sd_json_dispatch_field dispatch_table[] = {
-                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,    offsetof(LookupParameters, ifindex), 0                 },
+                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,   offsetof(LookupParameters, ifindex), SD_JSON_RELAX     },
                 { "family",  _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,    offsetof(LookupParameters, family),  SD_JSON_MANDATORY },
                 { "address", SD_JSON_VARIANT_ARRAY,         json_dispatch_address,   0,                                   SD_JSON_MANDATORY },
                 { "flags",   _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint64, offsetof(LookupParameters, flags),   0                 },
@@ -517,9 +514,6 @@ static int vl_method_resolve_address(sd_varlink *link, sd_json_variant *paramete
         if (r != 0)
                 return r;
 
-        if (p.ifindex < 0)
-                return sd_varlink_error_invalid_parameter(link, JSON_VARIANT_STRING_CONST("ifindex"));
-
         if (!IN_SET(p.family, AF_INET, AF_INET6))
                 return sd_varlink_error_invalid_parameter(link, JSON_VARIANT_STRING_CONST("family"));
 
@@ -968,12 +962,12 @@ fail:
 
 static int vl_method_resolve_service(sd_varlink* link, sd_json_variant* parameters, sd_varlink_method_flags_t flags, void* userdata) {
         static const sd_json_dispatch_field dispatch_table[] = {
-                { "name",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(LookupParametersResolveService, name),    0              },
-                { "type",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(LookupParametersResolveService, type),    0              },
+                { "name",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(LookupParametersResolveService, name),    0                 },
+                { "type",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(LookupParametersResolveService, type),    0                 },
                 { "domain",  SD_JSON_VARIANT_STRING,        sd_json_dispatch_const_string, offsetof(LookupParametersResolveService, domain),  SD_JSON_MANDATORY },
-                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,          offsetof(LookupParametersResolveService, ifindex), 0              },
-                { "family",  _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,          offsetof(LookupParametersResolveService, family),  0              },
-                { "flags",   _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint64,       offsetof(LookupParametersResolveService, flags),   0              },
+                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,         offsetof(LookupParametersResolveService, ifindex), SD_JSON_RELAX     },
+                { "family",  _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,          offsetof(LookupParametersResolveService, family),  0                 },
+                { "flags",   _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint64,       offsetof(LookupParametersResolveService, flags),   0                 },
                 {}
         };
 
@@ -998,9 +992,6 @@ static int vl_method_resolve_service(sd_varlink* link, sd_json_variant* paramete
         if (r != 0)
                 return r;
 
-        if (p.ifindex < 0)
-                return sd_varlink_error_invalid_parameter(link, JSON_VARIANT_STRING_CONST("ifindex"));
-
         if (!IN_SET(p.family, AF_INET, AF_INET6, AF_UNSPEC))
                 return sd_varlink_error_invalid_parameter(link, JSON_VARIANT_STRING_CONST("family"));
 
@@ -1123,7 +1114,7 @@ finish:
 
 static int vl_method_resolve_record(sd_varlink *link, sd_json_variant *parameters, sd_varlink_method_flags_t flags, void *userdata) {
         static const sd_json_dispatch_field dispatch_table[] = {
-                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_int,    offsetof(LookupParameters, ifindex), 0                 },
+                { "ifindex", _SD_JSON_VARIANT_TYPE_INVALID, json_dispatch_ifindex,   offsetof(LookupParameters, ifindex), SD_JSON_RELAX     },
                 { "name",    SD_JSON_VARIANT_STRING,        sd_json_dispatch_string, offsetof(LookupParameters, name),    SD_JSON_MANDATORY },
                 { "class",   _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint16, offsetof(LookupParameters, class),   0                 },
                 { "type",    _SD_JSON_VARIANT_TYPE_INVALID, sd_json_dispatch_uint16, offsetof(LookupParameters, type),    SD_JSON_MANDATORY },
@@ -1150,9 +1141,6 @@ static int vl_method_resolve_record(sd_varlink *link, sd_json_variant *parameter
         if (r != 0)
                 return r;
 
-        if (p.ifindex < 0)
-                return sd_varlink_error_invalid_parameter(link, JSON_VARIANT_STRING_CONST("ifindex"));
-
         r = dns_name_is_valid(p.name);
         if (r < 0)
                 return r;