lldp: add sd_lldp_tlv_packet_get_destination_type()

It can be useful to know the destination address of a LLDP frame
because it determines the scope of propagation of the frame and thus
this information be used to know whether the neighbor is connected to
the same physical link.

See clause 7.1 of IEEE Std 802.1AB-2009.

src/libsystemd-network/lldp-tlv.c

@@ -539,3 +539,20 @@ int sd_lldp_packet_read_system_capability(tlv_packet *tlv, uint16_t *data) {
 
         return r;
 }
+
+int sd_lldp_packet_get_destination_type(tlv_packet *tlv, int *dest) {
+        assert_return(tlv, -EINVAL);
+        assert_return(dest, -EINVAL);
+
+        /* 802.1AB-2009, Table 7-1 */
+        if (!memcmp(&tlv->mac, LLDP_MAC_NEAREST_BRIDGE, ETH_ALEN))
+                *dest = SD_LLDP_DESTINATION_TYPE_NEAREST_BRIDGE;
+        else if (!memcmp(&tlv->mac, LLDP_MAC_NEAREST_NON_TPMR_BRIDGE, ETH_ALEN))
+                *dest = SD_LLDP_DESTINATION_TYPE_NEAREST_NON_TPMR_BRIDGE;
+        else if (!memcmp(&tlv->mac, LLDP_MAC_NEAREST_CUSTOMER_BRIDGE, ETH_ALEN))
+                *dest = SD_LLDP_DESTINATION_TYPE_NEAREST_CUSTOMER_BRIDGE;
+        else
+                return -EINVAL;
+
+        return 0;
+}

src/libsystemd-network/lldp-tlv.h

@@ -43,6 +43,10 @@ struct tlv_section {
         LIST_FIELDS(tlv_section, section);
 };
 
+#define LLDP_MAC_NEAREST_BRIDGE          (uint8_t[]) { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x0e }
+#define LLDP_MAC_NEAREST_NON_TPMR_BRIDGE (uint8_t[]) { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x03 }
+#define LLDP_MAC_NEAREST_CUSTOMER_BRIDGE (uint8_t[]) { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 }
+
 int tlv_section_new(tlv_section **ret);
 void tlv_section_free(tlv_section *ret);
 

src/libsystemd-network/test-lldp.c

@@ -202,6 +202,15 @@ static int lldp_parse_ttl_tlv(tlv_packet *m) {
         return 0;
 }
 
+static int lldp_get_destination_type(tlv_packet *m) {
+        int dest;
+
+        assert_se(sd_lldp_packet_get_destination_type(m, &dest) >= 0);
+        assert_se(dest == SD_LLDP_DESTINATION_TYPE_NEAREST_BRIDGE);
+
+        return 0;
+}
+
 static int lldp_parse_tlv_packet(tlv_packet *m, int len) {
         uint8_t subtype;
 
@@ -212,6 +221,8 @@ static int lldp_parse_tlv_packet(tlv_packet *m, int len) {
         assert_se(lldp_parse_ttl_tlv(m) >= 0);
         assert_se(lldp_parse_system_desc_tlv(m) >= 0);
 
+        assert_se(lldp_get_destination_type(m) >= 0);
+
         return 0;
 }
 

src/systemd/sd-lldp.h

@@ -28,6 +28,12 @@ enum {
         SD_LLDP_EVENT_UPDATE_INFO       = 0,
 };
 
+enum {
+        SD_LLDP_DESTINATION_TYPE_NEAREST_BRIDGE,
+        SD_LLDP_DESTINATION_TYPE_NEAREST_NON_TPMR_BRIDGE,
+        SD_LLDP_DESTINATION_TYPE_NEAREST_CUSTOMER_BRIDGE,
+};
+
 typedef struct sd_lldp sd_lldp;
 typedef struct tlv_packet sd_lldp_packet;
 
@@ -56,4 +62,6 @@ int sd_lldp_packet_read_port_description(sd_lldp_packet *tlv, char **data, uint1
 sd_lldp_packet *sd_lldp_packet_ref(sd_lldp_packet *tlv);
 sd_lldp_packet *sd_lldp_packet_unref(sd_lldp_packet *tlv);
 
+int sd_lldp_packet_get_destination_type(sd_lldp_packet *tlv, int *dest);
+
 int sd_lldp_get_packets(sd_lldp *lldp, sd_lldp_packet ***tlvs);