backported supernode selection by MAC address to 3.0 as it also fixes a rarely occuring bug found in general supernode selection

edge.8

@@ -105,6 +105,10 @@ compress outgoing data packets, -z1 = lzo1x, disabled by default
 \fB\-\-select-rtt\fR
 select supernode by round trip time if several to choose from (federation),
 defaults to load-based selection strategy if not provided.
+.TP
+\fB\-\-select-mac\fR
+select supernode by MAC address if several to choose from (federation),
+lowest MAC address first.
 .SH TAP DEVICE AND OVERLAY NETWORK CONFIGURATION
 .TP
 \fB\-a \fR[\fImode\fR]<\fIip\fR>[\fI/n\fR]

include/n2n_typedefs.h

@@ -288,7 +288,7 @@ typedef char n2n_version_t[N2N_VERSION_STRING_SIZE];
 
 #define SN_SELECTION_STRATEGY_LOAD       1
 #define SN_SELECTION_STRATEGY_RTT        2
-#define SN_SELECTION_STRATEGY_MAC        3 /* REVISIT: not implemented yet */
+#define SN_SELECTION_STRATEGY_MAC        3
 
 
 typedef struct n2n_ip_subnet {

src/edge.c

@@ -232,6 +232,7 @@ static void help (int level) {
           "\n                      [-r]  enable packet forwarding through n2n community"
           "\n                      [-E]  accept multicast MAC addresses"
           "\n            [--select-rtt]  select supernode by round trip time"
+          "\n            [--select-mac]  select supernode by MAC address"
 #ifndef WIN32
           "\n                      [-f]  do not fork but run in foreground"
 #endif
@@ -290,7 +291,8 @@ static void help (int level) {
                                      "-z2 = zstd, "
 #endif
                                      "disabled by default\n");
-        printf("--select-rtt       | supernode selection based on round trip time (default:\n"
+        printf("--select-rtt       | supernode selection based on round trip time\n"
+               "--select-mac       | supernode selection based on MAC address (default:\n"
                "                   | by load)\n");
 
         printf ("\n");
@@ -737,7 +739,14 @@ static int setOption (int optkey, char *optargument, n2n_tuntap_priv_config_t *e
             break;
         }
 
-        case ']': /* password for management port */ {
+        case ']': /* mac-address-based supernode selection strategy */ {
+            // overwrites the default load-based strategy
+            conf->sn_selection_strategy = SN_SELECTION_STRATEGY_MAC;
+
+            break;
+        }
+
+        case '{': /* password for management port */ {
             conf->mgmt_password_hash = pearson_hash_64((uint8_t*)optargument, strlen(optargument));
 
             break;
@@ -797,7 +806,8 @@ static const struct option long_options[] =
         { "verbose",             no_argument,       NULL, 'v' },
         { "help",                no_argument,       NULL, '@' }, /* internal special character '@' to identify long help case */
         { "select-rtt",          no_argument,       NULL, '[' }, /*                            '['             rtt selection strategy */
-        { "management-password", required_argument, NULL, ']' }, /*                            ']'             management port password */
+        { "select-mac",          no_argument,       NULL, ']' }, /*                            ']'             mac selection strategy */
+        { "management-password", required_argument, NULL, '{' }, /*                            '{'             management port password */
         { NULL,                  0,                 NULL,  0  }
     };
 

src/sn_selection.c

@@ -88,7 +88,17 @@ int sn_selection_criterion_calculate (n2n_edge_t *eee, peer_info_t *peer, SN_SEL
         }
 
         case SN_SELECTION_STRATEGY_RTT: {
-            peer->selection_criterion = (SN_SELECTION_CRITERION_DATA_TYPE)(time_stamp() >> 22) - common_data;
+            peer->selection_criterion = (SN_SELECTION_CRITERION_DATA_TYPE)((uint32_t)time_stamp() >> 22) - common_data;
+            break;
+        }
+
+        case SN_SELECTION_STRATEGY_MAC: {
+            peer->selection_criterion = 0;
+            memcpy(&peer->selection_criterion, /* leftbound, don't mess with pointer arithmetics */
+                   peer->mac_addr,
+                   N2N_MAC_SIZE);
+            peer->selection_criterion = be64toh(peer->selection_criterion);
+            peer->selection_criterion >>= (sizeof(peer->selection_criterion) - N2N_MAC_SIZE) * 8; /* rightbound */
             break;
         }
 
@@ -120,7 +130,12 @@ int sn_selection_criterion_common_data_default (n2n_edge_t *eee) {
         }
 
         case SN_SELECTION_STRATEGY_RTT: {
-            eee->sn_selection_criterion_common_data = (SN_SELECTION_CRITERION_DATA_TYPE)(time_stamp() >> 22);
+            eee->sn_selection_criterion_common_data = (SN_SELECTION_CRITERION_DATA_TYPE)((uint32_t)time_stamp() >> 22);
+            break;
+        }
+
+        case SN_SELECTION_STRATEGY_MAC: {
+            eee->sn_selection_criterion_common_data = 0;
             break;
         }
 
@@ -145,8 +160,15 @@ static SN_SELECTION_CRITERION_DATA_TYPE sn_selection_criterion_common_read (n2n_
 /* Function that compare two selection_criterion fields and sorts them in ascending order. */
 static int sn_selection_criterion_sort (peer_info_t *a, peer_info_t *b) {
 
+    int ret = 0;
+
     // comparison function for sorting supernodes in ascending order of their selection_criterion.
-    return (a->selection_criterion - b->selection_criterion);
+    if(a->selection_criterion > b->selection_criterion)
+        ret = 1;
+    else if(a->selection_criterion < b->selection_criterion)
+        ret = -2;
+
+    return ret;
 }
 
 
@@ -177,7 +199,7 @@ SN_SELECTION_CRITERION_DATA_TYPE sn_selection_criterion_gather_data (n2n_sn_t *s
         data += tmp;
     }
 
-    return htobe32(data);
+    return htobe64(data);
 }
 
 
@@ -195,7 +217,7 @@ extern char * sn_selection_criterion_str (n2n_edge_t *eee, selection_criterion_s
     // keep off the super-big values (used for "bad" or "good" or "undetermined" supernodes,
     // easier to sort to the end of the list).
     // Alternatively, typecast to (int16_t) and check for greater or equal zero
-    if(peer->selection_criterion < (UINT32_MAX >> 2)) {
+    if(peer->selection_criterion < (UINT64_MAX >> 2)) {
 
         switch(eee->conf.sn_selection_strategy) {
 
@@ -209,6 +231,11 @@ extern char * sn_selection_criterion_str (n2n_edge_t *eee, selection_criterion_s
                 break;
             }
 
+            case SN_SELECTION_STRATEGY_MAC: {
+                chars = snprintf(out, SN_SELECTION_CRITERION_BUF_SIZE, "%s", (int64_t)peer->selection_criterion > 0 ? "active" : "");
+                break;
+            }
+
             default: {
                 // this should never happen
                 traceEvent(TRACE_ERROR, "selection_criterion unknown selection strategy configuration");