diff --git a/cbench/cbench.c b/cbench/cbench.c
index 70fed93..cdf8492 100644
--- a/cbench/cbench.c
+++ b/cbench/cbench.c
@@ -45,6 +45,7 @@ struct myargs my_options[] = {
     {"connect-group-size",  'I', "number of switches in a connection delay group", MYARGS_INTEGER, {.integer = 1}},
     {"learn-dst-macs",  'L', "send gratuitious ARP replies to learn destination macs before testing", MYARGS_FLAG, {.flag = 1}},
     {"dpid-offset",  'o', "switch DPID offset", MYARGS_INTEGER, {.integer = 1}},
+    {"igmp-test", 'g', "IGMP join leave test", MYARGS_FLAG, {.flag = 0}},
     {0, 0, 0, 0}
 };
 
@@ -257,6 +258,7 @@ int main(int argc, char * argv[])
     int     learn_dst_macs = myargs_get_default_flag(my_options, "learn-dst-macs");
     int     dpid_offset = myargs_get_default_integer(my_options, "dpid-offset");
     int     mode = MODE_LATENCY;
+    int     igmp_test = myargs_get_default_flag(my_options, "igmp-test");
     int     i,j;
 
     const struct option * long_opts = myargs_to_long(my_options);
@@ -326,6 +328,9 @@ int main(int argc, char * argv[])
             case 'o':
                 dpid_offset = atoi(optarg);
                 break;
+            case 'g':
+                igmp_test = 1;
+                break;
             default: 
                 myargs_usage(my_options, PROG_TITLE, "help message", NULL, 1);
         }
@@ -388,7 +393,8 @@ int main(int argc, char * argv[])
         if(debug)
             fprintf(stderr,"Initializing switch %d ... ", i+1);
         fflush(stderr);
-        fakeswitch_init(&fakeswitches[i],dpid_offset+i,sock,BUFLEN, debug, delay, mode, total_mac_addresses, learn_dst_macs);
+        fakeswitch_init(&fakeswitches[i],dpid_offset+i,sock,BUFLEN, debug, delay, mode, total_mac_addresses,
+                        learn_dst_macs, igmp_test);
         if(debug)
             fprintf(stderr," :: done.\n");
         fflush(stderr);
diff --git a/cbench/fakeswitch.c b/cbench/fakeswitch.c
index a424d14..d3f16de 100644
--- a/cbench/fakeswitch.c
+++ b/cbench/fakeswitch.c
@@ -25,12 +25,14 @@ static int make_stats_desc_reply(struct ofp_stats_request * req, char * buf, int
 static int parse_set_config(struct ofp_header * msg);
 static int make_config_reply( int xid, char * buf, int buflen);
 static int make_vendor_reply(int xid, char * buf, int buflen);
-static int make_packet_in(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address);
 static int packet_out_is_lldp(struct ofp_packet_out * po);
 static void fakeswitch_handle_write(struct fakeswitch *fs);
 static void fakeswitch_learn_dstmac(struct fakeswitch *fs);
 void fakeswitch_change_status_now (struct fakeswitch *fs, int new_status);
 void fakeswitch_change_status (struct fakeswitch *fs, int new_status);
+static int make_packet_in_default(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address);
+static int make_packet_in_igmp(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address);
+static int (*make_packet_in)(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address);
 
 static struct ofp_switch_config Switch_config = {
 	.header = { 	OFP_VERSION,
@@ -51,7 +53,7 @@ static inline uint64_t ntohll(uint64_t n)
     return htonl(1) == 1 ? n : ((uint64_t) ntohl(n) << 32) | ntohl(n >> 32);
 }
 
-void fakeswitch_init(struct fakeswitch *fs, int dpid, int sock, int bufsize, int debug, int delay, enum test_mode mode, int total_mac_addresses, int learn_dstmac)
+void fakeswitch_init(struct fakeswitch *fs, int dpid, int sock, int bufsize, int debug, int delay, enum test_mode mode, int total_mac_addresses, int learn_dstmac, int igmp_test)
 {
     char buf[BUFLEN];
     struct ofp_header ofph;
@@ -62,6 +64,8 @@ void fakeswitch_init(struct fakeswitch *fs, int dpid, int sock, int bufsize, int
     fs->outbuf = msgbuf_new(bufsize);
     fs->probe_state = 0;
     fs->mode = mode;
+    fs->igmp_test = igmp_test;
+    make_packet_in = igmp_test ? make_packet_in_igmp : make_packet_in_default;
     fs->probe_size = make_packet_in(fs->id, 0, 0, buf, BUFLEN, fs->current_mac_address++);
     fs->count = 0;
     fs->switch_status = START;
@@ -71,7 +75,6 @@ void fakeswitch_init(struct fakeswitch *fs, int dpid, int sock, int bufsize, int
     fs->xid = 1;
     fs->learn_dstmac = learn_dstmac;
     fs->current_buffer_id = 1;
-  
     ofph.version = OFP_VERSION;
     ofph.type = OFPT_HELLO;
     ofph.length = htons(sizeof(ofph));
@@ -289,8 +292,54 @@ static int packet_out_is_lldp(struct ofp_packet_out * po){
 	return ethertype == ETHERTYPE_LLDP;
 }
 
+static int make_packet_in_igmp(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address)
+{
+    struct ofp_packet_in * pi;
+    struct ether_header * eth;
+    static char fake_igmp_join[] = {
+        0x97,0x0a,0x00,0x4c,0x00,0x00,0x00,0x00,0x00,0x00,0x01,
+        0x01,0x00,0x40,0x00,0x01,0x00,0x00,0x80,0x00,0x00,0x00,
+        0x00,0x01,0x00,0x00,0x00,0x00,0x00,0x02,0x08,0x00,0x46,
+        0xc0,0x00,0x2c,0x00,0x01,0x00,0x00,0x01,0x02,0x3f,0x04,
+        0x01,0x02,0x03,0x04,0xe0,0x00,0x01,0x01,0x94,0x04,0x00,
+        0x00,0x22,0x00,0xf6,0xf5,0x00,0x00,0x00,0x01,0x01,0x00,
+        0x00,0x01,0xe2,0x00,0x00,0x01,0x01,0x02,0x03,0x04,
+    };
+    static char fake_igmp_leave[] = {
+        0x97,0x0a,0x00,0x4c,0x00,0x00,0x00,0x00,0x00,0x00,0x01,
+        0x01,0x00,0x40,0x00,0x01,0x00,0x00,0x80,0x00,0x00,0x00,
+        0x00,0x01,0x00,0x00,0x00,0x00,0x00,0x02,0x08,0x00,0x46,
+        0xc0,0x00,0x2c,0x00,0x01,0x00,0x00,0x01,0x02,0x3f,0x04,
+        0x01,0x02,0x03,0x04,0xe0,0x00,0x01,0x01,0x94,0x04,0x00,
+        0x00,0x22,0x00,0xf5,0xf5,0x00,0x00,0x00,0x01,0x02,0x00,
+        0x00,0x01,0xe2,0x00,0x00,0x01,0x01,0x02,0x03,0x04,
+    };
+    static char *fake_bufs[2] = { fake_igmp_join, fake_igmp_leave };
+    static int fake_size_map[2] = { (int)sizeof(fake_igmp_join), (int)sizeof(fake_igmp_leave) };
+    static int idx;
+    int cur_idx = idx;
+    int buf_size = fake_size_map[cur_idx];
+    char *fake;
+    fake = fake_bufs[cur_idx];
+    idx ^= 1;
+    assert(buflen > buf_size);
+    memcpy(buf, fake, buf_size);
+    pi = (struct ofp_packet_in *) buf;
+    pi->header.version = OFP_VERSION;
+    pi->header.xid = htonl(xid);
+    pi->buffer_id = htonl(buffer_id);
+    eth = (struct ether_header * ) pi->data;
+    // copy into src mac addr; only 4 bytes, but should suffice to not confuse
+    // the controller; don't overwrite first byte
+    memcpy(&eth->ether_shost[1], &mac_address, sizeof(mac_address));
+    // mark this as coming from us, mostly for debug
+    eth->ether_dhost[5] = switch_id;
+    eth->ether_shost[5] = switch_id;
+    return buf_size;
+}
+
 /***********************************************************************/
-static int make_packet_in(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address)
+static int make_packet_in_default(int switch_id, int xid, int buffer_id, char * buf, int buflen, int mac_address)
 {
     struct ofp_packet_in * pi;
     struct ether_header * eth;
@@ -387,6 +436,7 @@ void fakeswitch_handle_read(struct fakeswitch *fs)
                 if(fs->switch_status == READY_TO_SEND && (fm->command == htons(OFPFC_ADD) || 
                         fm->command == htons(OFPFC_MODIFY_STRICT)))
                 {
+                    debug_msg(fs, "Got FLOW MOD response\n");
                     fs->count++;        // got response to what we went
                     fs->probe_state--;
                 }
@@ -488,6 +538,7 @@ static void fakeswitch_handle_write(struct fakeswitch *fs)
         else if ((fs->mode == MODE_THROUGHPUT) && 
                 (msgbuf_count_buffered(fs->outbuf) < throughput_buffer))  // keep buffer full
             send_count = (throughput_buffer - msgbuf_count_buffered(fs->outbuf)) / fs->probe_size;
+
         for (i = 0; i < send_count; i++)
         {
             // queue up packet
diff --git a/cbench/fakeswitch.h b/cbench/fakeswitch.h
index d0352e7..26eb202 100644
--- a/cbench/fakeswitch.h
+++ b/cbench/fakeswitch.h
@@ -39,6 +39,7 @@ struct fakeswitch
     int current_mac_address;
     int learn_dstmac;
     int current_buffer_id;
+    int igmp_test;
 };
 
 /*** Initialize an already allocated fakeswitch
@@ -54,7 +55,7 @@ struct fakeswitch
  * @param total_mac_addresses      The total number of unique mac addresses
  *                                 to use for packet ins from this switch
  */
-void fakeswitch_init(struct fakeswitch *fs, int dpid, int sock, int bufsize, int debug, int delay, enum test_mode mode, int total_mac_addresses, int learn_dstmac);
+void fakeswitch_init(struct fakeswitch *fs, int dpid, int sock, int bufsize, int debug, int delay, enum test_mode mode, int total_mac_addresses, int learn_dstmac, int igmp_test);
 
 
 /*** Set the desired flags for poll()