diff --git a/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp b/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
index 990423802..eb62222fb 100644
--- a/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
+++ b/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
@@ -123,14 +123,14 @@ int BitstreamManager::block_path_id(const ConfigBlockId& block_id) const {
   return block_path_ids_[block_id];
 }
 
-std::vector<std::string> BitstreamManager::block_input_net_ids(const ConfigBlockId& block_id) const {
+std::string BitstreamManager::block_input_net_ids(const ConfigBlockId& block_id) const {
   /* Ensure the input ids are valid */
   VTR_ASSERT(true == valid_block_id(block_id));
 
   return block_input_net_ids_[block_id];
 }
 
-std::vector<std::string> BitstreamManager::block_output_net_ids(const ConfigBlockId& block_id) const {
+std::string BitstreamManager::block_output_net_ids(const ConfigBlockId& block_id) const {
   /* Ensure the input ids are valid */
   VTR_ASSERT(true == valid_block_id(block_id));
 
@@ -246,29 +246,13 @@ void BitstreamManager::add_path_id_to_block(const ConfigBlockId& block, const in
   block_path_ids_[block] = path_id;
 }
 
-void BitstreamManager::reserve_block_input_net_ids(const ConfigBlockId& block,
-                                                   const size_t& num_input_net_ids) {
-  /* Ensure the input ids are valid */
-  VTR_ASSERT(true == valid_block_id(block));
-
-  block_input_net_ids_[block].reserve(num_input_net_ids);
-}
-
 void BitstreamManager::add_input_net_id_to_block(const ConfigBlockId& block,
                                                  const std::string& input_net_id) {
   /* Ensure the input ids are valid */
   VTR_ASSERT(true == valid_block_id(block));
 
   /* Add the bit to the block */
-  block_input_net_ids_[block].push_back(input_net_id);
-}
-
-void BitstreamManager::reserve_block_output_net_ids(const ConfigBlockId& block,
-                                                    const size_t& num_output_net_ids) {
-  /* Ensure the input ids are valid */
-  VTR_ASSERT(true == valid_block_id(block));
-
-  block_output_net_ids_[block].reserve(num_output_net_ids);
+  block_input_net_ids_[block] = input_net_id;
 }
 
 void BitstreamManager::add_output_net_id_to_block(const ConfigBlockId& block,
@@ -277,7 +261,7 @@ void BitstreamManager::add_output_net_id_to_block(const ConfigBlockId& block,
   VTR_ASSERT(true == valid_block_id(block));
 
   /* Add the bit to the block */
-  block_output_net_ids_[block].push_back(output_net_id);
+  block_output_net_ids_[block] = output_net_id;
 }
 
 /******************************************************************************
diff --git a/libopenfpga/libfpgabitstream/src/bitstream_manager.h b/libopenfpga/libfpgabitstream/src/bitstream_manager.h
index 6f2e56c38..84c3ec97c 100644
--- a/libopenfpga/libfpgabitstream/src/bitstream_manager.h
+++ b/libopenfpga/libfpgabitstream/src/bitstream_manager.h
@@ -138,10 +138,10 @@ class BitstreamManager {
     int block_path_id(const ConfigBlockId& block_id) const;
 
     /* Find input net ids of a block */
-    std::vector<std::string> block_input_net_ids(const ConfigBlockId& block_id) const;
+    std::string block_input_net_ids(const ConfigBlockId& block_id) const;
 
     /* Find input net ids of a block */
-    std::vector<std::string> block_output_net_ids(const ConfigBlockId& block_id) const;
+    std::string block_output_net_ids(const ConfigBlockId& block_id) const;
 
   public:  /* Public Mutators */
     /* Add a new configuration bit to the bitstream manager */
@@ -177,15 +177,9 @@ class BitstreamManager {
     /* Add a path id to a block */
     void add_path_id_to_block(const ConfigBlockId& block, const int& path_id);
  
-    /* Reserve input net ids for a block */
-    void reserve_block_input_net_ids(const ConfigBlockId& block, const size_t& num_input_net_ids);
-
     /* Add an input net id to a block */
     void add_input_net_id_to_block(const ConfigBlockId& block, const std::string& input_net_id);
 
-    /* Reserve output net ids for a block */
-    void reserve_block_output_net_ids(const ConfigBlockId& block, const size_t& num_output_net_ids);
-
     /* Add an output net id to a block */
     void add_output_net_id_to_block(const ConfigBlockId& block, const std::string& output_net_id);
 
@@ -233,8 +227,8 @@ class BitstreamManager {
      *   -Bitstream manager will NOT check if the id is good for bitstream builders
      *    It just store the results
      */
-    vtr::vector<ConfigBlockId, std::vector<std::string>> block_input_net_ids_; 
-    vtr::vector<ConfigBlockId, std::vector<std::string>> block_output_net_ids_; 
+    vtr::vector<ConfigBlockId, std::string> block_input_net_ids_; 
+    vtr::vector<ConfigBlockId, std::string> block_output_net_ids_; 
 
     /* Unique id of a bit in the Bitstream */
     size_t num_bits_; 
diff --git a/libopenfpga/libfpgabitstream/src/read_xml_arch_bitstream.cpp b/libopenfpga/libfpgabitstream/src/read_xml_arch_bitstream.cpp
index 04e0918f1..be39c4e64 100644
--- a/libopenfpga/libfpgabitstream/src/read_xml_arch_bitstream.cpp
+++ b/libopenfpga/libfpgabitstream/src/read_xml_arch_bitstream.cpp
@@ -62,9 +62,16 @@ void rec_read_xml_bitstream_block(pugi::xml_node& xml_bitstream_block,
       input_nets[id] = net_name; 
     } 
 
+    std::string input_nets_str;
+    bool need_splitter = false;
     for (const std::string& input_net : input_nets) {
-      bitstream_manager.add_input_net_id_to_block(curr_block, input_net); 
+      if (true == need_splitter) {
+        input_nets_str += std::string(" ");
+      }
+      input_nets_str += input_net;
+      need_splitter = true;
     }
+    bitstream_manager.add_input_net_id_to_block(curr_block, input_nets_str); 
   }
 
   /* Parse output nets if defined */
@@ -86,9 +93,16 @@ void rec_read_xml_bitstream_block(pugi::xml_node& xml_bitstream_block,
       output_nets[id] = net_name; 
     } 
 
+    std::string output_nets_str;
+    bool need_splitter = false;
     for (const std::string& output_net : output_nets) {
-      bitstream_manager.add_output_net_id_to_block(curr_block, output_net); 
+      if (true == need_splitter) {
+        output_nets_str += std::string(" ");
+      }
+      output_nets_str += output_net;
+      need_splitter = true;
     }
+    bitstream_manager.add_output_net_id_to_block(curr_block, output_nets_str); 
   }
 
   /* Parse configuration bits */
diff --git a/libopenfpga/libfpgabitstream/src/write_xml_arch_bitstream.cpp b/libopenfpga/libfpgabitstream/src/write_xml_arch_bitstream.cpp
index 0cc8c88b0..17e94cd15 100644
--- a/libopenfpga/libfpgabitstream/src/write_xml_arch_bitstream.cpp
+++ b/libopenfpga/libfpgabitstream/src/write_xml_arch_bitstream.cpp
@@ -13,6 +13,7 @@
 
 /* Headers from openfpgautil library */
 #include "openfpga_digest.h"
+#include "openfpga_tokenizer.h"
 
 #include "openfpga_reserved_words.h"
 
@@ -95,7 +96,9 @@ void rec_write_block_bitstream_to_xml_file(std::fstream& fp,
     write_tab_to_file(fp, hierarchy_level + 1);
     fp << "<input_nets>\n";
     size_t path_counter = 0;
-    for (const std::string& net : bitstream_manager.block_input_net_ids(block)) {
+    /* Split with space */
+    StringToken input_net_tokenizer(bitstream_manager.block_input_net_ids(block));
+    for (const std::string& net : input_net_tokenizer.split(std::string(" "))) {
       write_tab_to_file(fp, hierarchy_level + 2);
       fp << "<path id=\"" << path_counter << "\"";
       fp << " net_name=\"";
@@ -113,7 +116,9 @@ void rec_write_block_bitstream_to_xml_file(std::fstream& fp,
     write_tab_to_file(fp, hierarchy_level + 1);
     fp << "<output_nets>\n";
     size_t path_counter = 0;
-    for (const std::string& net : bitstream_manager.block_output_net_ids(block)) {
+    /* Split with space */
+    StringToken output_net_tokenizer(bitstream_manager.block_output_net_ids(block));
+    for (const std::string& net : output_net_tokenizer.split(std::string(" "))) {
       write_tab_to_file(fp, hierarchy_level + 2);
       fp << "<path id=\"" << path_counter << "\"";
       fp << " net_name=\"";
diff --git a/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp b/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp
index f970a746c..550f6e86f 100644
--- a/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp
+++ b/openfpga/src/fpga_bitstream/build_grid_bitstream.cpp
@@ -214,20 +214,33 @@ void build_physical_block_pin_interc_bitstream(BitstreamManager& bitstream_manag
     bitstream_manager.add_block_bits(mux_mem_block, mux_bitstream);
     /* Record path ids, input and output nets */
     bitstream_manager.add_path_id_to_block(mux_mem_block, mux_input_pin_id);
-    bitstream_manager.reserve_block_input_net_ids(mux_mem_block, input_nets.size());
+
+    /* Add input nets */
+    std::string input_net_ids;
+    
+    bool need_splitter = false;
     for (const AtomNetId& input_net : input_nets) {
-      if (true == atom_ctx.nlist.valid_net_id(input_net)) {
-        bitstream_manager.add_input_net_id_to_block(mux_mem_block, atom_ctx.nlist.net_name(input_net));
-      } else {
-        bitstream_manager.add_input_net_id_to_block(mux_mem_block, std::string("unmapped"));
+      /* Add a space as a splitter*/
+      if (true == need_splitter) {
+        input_net_ids += std::string(" ");
       }
+      if (true == atom_ctx.nlist.valid_net_id(input_net)) {
+        input_net_ids += atom_ctx.nlist.net_name(input_net);
+      } else {
+        input_net_ids += std::string("unmapped");
+      }
+      need_splitter = true;
     }
+    bitstream_manager.add_input_net_id_to_block(mux_mem_block, input_net_ids);
+
+    /* Add output nets */
+    std::string output_net_ids;
     if (true == atom_ctx.nlist.valid_net_id(output_net)) {
-    bitstream_manager.reserve_block_output_net_ids(mux_mem_block, 1);
-      bitstream_manager.add_output_net_id_to_block(mux_mem_block, atom_ctx.nlist.net_name(output_net));
+      output_net_ids += atom_ctx.nlist.net_name(output_net);
     } else {
-      bitstream_manager.add_output_net_id_to_block(mux_mem_block, std::string("unmapped"));
+      output_net_ids += std::string("unmapped");
     }
+    bitstream_manager.add_output_net_id_to_block(mux_mem_block, output_net_ids);
 
     break;
   }
diff --git a/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp b/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp
index 4f25a3a44..012222369 100644
--- a/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp
+++ b/openfpga/src/fpga_bitstream/build_routing_bitstream.cpp
@@ -102,22 +102,34 @@ void build_switch_block_mux_bitstream(BitstreamManager& bitstream_manager,
   bitstream_manager.add_block_bits(mux_mem_block, mux_bitstream);
   /* Record path ids, input and output nets */
   bitstream_manager.add_path_id_to_block(mux_mem_block, path_id);
-  bitstream_manager.reserve_block_input_net_ids(mux_mem_block, input_nets.size());
+
+  /* Add input nets */
+  bool need_splitter = false;
+  std::string input_net_ids;
   for (const ClusterNetId& input_net : input_nets) {
+    /* Add a space as a splitter*/
+    if (true == need_splitter) {
+      input_net_ids += std::string(" ");
+    }
     AtomNetId input_atom_net = atom_ctx.lookup.atom_net(input_net);
     if (true == atom_ctx.nlist.valid_net_id(input_atom_net)) {
-      bitstream_manager.add_input_net_id_to_block(mux_mem_block, atom_ctx.nlist.net_name(input_atom_net));
+      input_net_ids += atom_ctx.nlist.net_name(input_atom_net);
     } else {
-      bitstream_manager.add_input_net_id_to_block(mux_mem_block, std::string("unmapped"));
+      input_net_ids += std::string("unmapped");
     }
+    need_splitter = true;
   }
+  bitstream_manager.add_input_net_id_to_block(mux_mem_block, input_net_ids);
+
+  /* Add output nets */
+  std::string output_net_ids;
   AtomNetId output_atom_net = atom_ctx.lookup.atom_net(output_net);
-  bitstream_manager.reserve_block_output_net_ids(mux_mem_block, 1);
   if (true == atom_ctx.nlist.valid_net_id(output_atom_net)) {
-    bitstream_manager.add_output_net_id_to_block(mux_mem_block, atom_ctx.nlist.net_name(output_atom_net));
+    output_net_ids += atom_ctx.nlist.net_name(output_atom_net);
   } else {
-    bitstream_manager.add_output_net_id_to_block(mux_mem_block, std::string("unmapped"));
+    output_net_ids += std::string("unmapped");
   }
+  bitstream_manager.add_output_net_id_to_block(mux_mem_block, output_net_ids);
 }
 
 /********************************************************************
@@ -291,22 +303,35 @@ void build_connection_block_mux_bitstream(BitstreamManager& bitstream_manager,
   bitstream_manager.add_block_bits(mux_mem_block, mux_bitstream);
   /* Record path ids, input and output nets */
   bitstream_manager.add_path_id_to_block(mux_mem_block, path_id);
-  bitstream_manager.reserve_block_input_net_ids(mux_mem_block, input_nets.size());
+
+  /* Add input nets */
+  bool need_splitter = false;
+  std::string input_net_ids;
   for (const ClusterNetId& input_net : input_nets) {
+    /* Add a space as a splitter*/
+    if (true == need_splitter) {
+      input_net_ids += std::string(" ");
+    }
     AtomNetId input_atom_net = atom_ctx.lookup.atom_net(input_net);
     if (true == atom_ctx.nlist.valid_net_id(input_atom_net)) {
-      bitstream_manager.add_input_net_id_to_block(mux_mem_block, atom_ctx.nlist.net_name(input_atom_net));
+      input_net_ids += atom_ctx.nlist.net_name(input_atom_net);
     } else {
-      bitstream_manager.add_input_net_id_to_block(mux_mem_block, std::string("unmapped"));
+      input_net_ids += std::string("unmapped");
     }
+    need_splitter = true;
   }
+  bitstream_manager.add_input_net_id_to_block(mux_mem_block, input_net_ids);
+
+  /* Add output nets */
+  std::string output_net_ids;
   AtomNetId output_atom_net = atom_ctx.lookup.atom_net(output_net);
-  bitstream_manager.reserve_block_output_net_ids(mux_mem_block, 1);
   if (true == atom_ctx.nlist.valid_net_id(output_atom_net)) {
-    bitstream_manager.add_output_net_id_to_block(mux_mem_block, atom_ctx.nlist.net_name(output_atom_net));
+    output_net_ids += atom_ctx.nlist.net_name(output_atom_net);
   } else {
-    bitstream_manager.add_output_net_id_to_block(mux_mem_block, std::string("unmapped"));
+    output_net_ids += std::string("unmapped");
   }
+  bitstream_manager.add_output_net_id_to_block(mux_mem_block, output_net_ids);
+
 }
 
 /********************************************************************