diff --git a/.gitignore b/.gitignore
index e6729457..cb24665d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -29,6 +29,7 @@
 
 # Vscode related
 .vscode/
+build/
 
 # CLion related
 .idea
diff --git a/lci/backend/ibv/lcisi_ibv_detail.c b/lci/backend/ibv/lcisi_ibv_detail.c
index 426c9380..7ab5c762 100644
--- a/lci/backend/ibv/lcisi_ibv_detail.c
+++ b/lci/backend/ibv/lcisi_ibv_detail.c
@@ -90,7 +90,7 @@ bool select_best_device_port(struct ibv_device** dev_list, int num_devices,
         continue;
       }
       // Check whether we can get its lid
-      if (port_attr.link_layer != IBV_LINK_LAYER_ETHERNET && !port_attr.lid) {
+      if (port_attr.link_layer == IBV_LINK_LAYER_INFINIBAND && !port_attr.lid) {
         fprintf(stderr, "Couldn't get local LID\n");
         continue;
       }
@@ -134,4 +134,121 @@ bool select_best_device_port(struct ibv_device** dev_list, int num_devices,
     LCI_Log(LCI_LOG_INFO, "ibv", "No device is available!\n");
     return false;
   }
+}
+
+typedef enum roce_version_t {
+  ROCE_V1,
+  ROCE_V2,
+  ROCE_VER_UNKNOWN
+} roce_version_t;
+
+roce_version_t query_gid_roce_version(LCISI_server_t* server,
+                                      unsigned gid_index)
+{
+  char buf[16];
+  int ret;
+  char* dev_name = ibv_get_device_name(server->ib_dev);
+
+  union ibv_gid gid;
+  ret = ibv_query_gid(server->dev_ctx, server->dev_port, gid_index, &gid);
+  if (ret == 0) {
+    ret = LCT_read_file(buf, sizeof(buf),
+                        "/sys/class/infiniband/%s/ports/%d/gid_attrs/types/%d",
+                        dev_name, server->dev_port, gid_index);
+    if (ret > 0) {
+      if (!strncmp(buf, "IB/RoCE v1", 10)) {
+        return ROCE_V1;
+      } else if (!strncmp(buf, "RoCE v2", 7)) {
+        return ROCE_V2;
+      }
+    }
+  }
+  LCI_Log(LCI_LOG_DEBUG, "ibv",
+          "failed to parse gid type '%s' (dev=%s port=%d index=%d)\n", buf,
+          dev_name, server->dev_port, gid_index);
+  return ROCE_VER_UNKNOWN;
+}
+
+bool test_roce_gid_index(LCISI_server_t* server, uint8_t gid_index)
+{
+  struct ibv_ah_attr ah_attr;
+  struct ibv_ah* ah;
+  union ibv_gid gid;
+
+  IBV_SAFECALL(
+      ibv_query_gid(server->dev_ctx, server->dev_port, gid_index, &gid));
+
+  memset(&ah_attr, 0, sizeof(ah_attr));
+  ah_attr.port_num = server->dev_port;
+  ah_attr.is_global = 1;
+  ah_attr.grh.dgid = gid;
+  ah_attr.grh.sgid_index = gid_index;
+  ah_attr.grh.hop_limit = 255;
+  ah_attr.grh.flow_label = 1;
+  ah_attr.dlid = 0xC000;
+
+  ah = ibv_create_ah(server->dev_pd, &ah_attr);
+  if (ah == NULL) {
+    LCI_Log(LCI_LOG_DEBUG, "ibv", "gid entry %d is not operational\n", gid_index);
+    return false;
+  }
+
+  ibv_destroy_ah(ah);
+  return true;
+}
+
+int select_best_gid_for_roce(LCISI_server_t* server)
+{
+  static const roce_version_t roce_prio[] = {
+      ROCE_V2,
+      ROCE_V1,
+      ROCE_VER_UNKNOWN,
+  };
+  int gid_tbl_len = server->port_attr.gid_tbl_len;
+
+  LCI_Log(LCI_LOG_DEBUG, "ibv", "RoCE gid auto selection among %d gids\n",
+          gid_tbl_len);
+  for (int prio_idx = 0; prio_idx < sizeof(roce_prio); prio_idx++) {
+    for (int i = 0; i < gid_tbl_len; i++) {
+      roce_version_t version = query_gid_roce_version(server, i);
+
+      if ((roce_prio[prio_idx] == version) && test_roce_gid_index(server, i)) {
+        LCI_Log(LCI_LOG_INFO, "ibv", "RoCE gid auto selection: use %d %d\n", i,
+                version);
+        return i;
+      }
+    }
+  }
+
+  const int default_gid = 0;
+  LCI_Log(LCI_LOG_INFO, "ibv",
+          "RoCE gid auto selection: fall back to the default gid %d\n",
+          default_gid);
+  return default_gid;  // default gid for roce
+}
+
+void gid_to_wire_gid(const union ibv_gid* gid, char wgid[])
+{
+  LCI_Assert(sizeof(union ibv_gid) == 16, "Unexpected ibv_gid size %d\n", sizeof(union ibv_gid));
+  uint32_t tmp_gid[4];
+  int i;
+
+  memcpy(tmp_gid, gid, sizeof(tmp_gid));
+  for (i = 0; i < 4; ++i) sprintf(&wgid[i * 8], "%08x", htobe32(tmp_gid[i]));
+}
+
+void wire_gid_to_gid(const char* wgid, union ibv_gid* gid)
+{
+  LCI_Assert(sizeof(union ibv_gid) == 16, "Unexpected ibv_gid size %d\n", sizeof(union ibv_gid));
+  char tmp[9];
+  __be32 v32;
+  int i;
+  uint32_t tmp_gid[4];
+
+  for (tmp[8] = 0, i = 0; i < 4; ++i) {
+    memcpy(tmp, wgid + i * 8, 8);
+    sscanf(tmp, "%x", &v32);
+    tmp_gid[i] = be32toh(v32);
+  }
+  memcpy(gid, tmp_gid, sizeof(*gid));
 }
\ No newline at end of file
diff --git a/lci/backend/ibv/lcisi_ibv_detail.h b/lci/backend/ibv/lcisi_ibv_detail.h
index d69c5f77..6b90ed83 100644
--- a/lci/backend/ibv/lcisi_ibv_detail.h
+++ b/lci/backend/ibv/lcisi_ibv_detail.h
@@ -6,28 +6,12 @@
 bool select_best_device_port(struct ibv_device** dev_list, int num_devices,
                              struct ibv_device** device_o, uint8_t* port_o);
 
-void gid_to_wire_gid(const union ibv_gid* gid, char wgid[])
-{
-  uint32_t tmp_gid[4];
-  int i;
+int select_best_gid_for_roce(LCISI_server_t* server);
 
-  memcpy(tmp_gid, gid, sizeof(tmp_gid));
-  for (i = 0; i < 4; ++i) sprintf(&wgid[i * 8], "%08x", htobe32(tmp_gid[i]));
-}
+const int WIRE_GID_NBYTES = 32;
 
-void wire_gid_to_gid(const char* wgid, union ibv_gid* gid)
-{
-  char tmp[9];
-  __be32 v32;
-  int i;
-  uint32_t tmp_gid[4];
+void gid_to_wire_gid(const union ibv_gid* gid, char wgid[]);
 
-  for (tmp[8] = 0, i = 0; i < 4; ++i) {
-    memcpy(tmp, wgid + i * 8, 8);
-    sscanf(tmp, "%x", &v32);
-    tmp_gid[i] = be32toh(v32);
-  }
-  memcpy(gid, tmp_gid, sizeof(*gid));
-}
+void wire_gid_to_gid(const char* wgid, union ibv_gid* gid);
 
 #endif
\ No newline at end of file
diff --git a/lci/backend/ibv/server_ibv.c b/lci/backend/ibv/server_ibv.c
index 318ee907..f6323f16 100644
--- a/lci/backend/ibv/server_ibv.c
+++ b/lci/backend/ibv/server_ibv.c
@@ -159,7 +159,7 @@ void LCISD_server_init(LCIS_server_t* s)
   if (rc != 0) {
     fprintf(stderr, "Unable to query port\n");
     exit(EXIT_FAILURE);
-  } else if (server->port_attr.link_layer != IBV_LINK_LAYER_ETHERNET &&
+  } else if (server->port_attr.link_layer == IBV_LINK_LAYER_INFINIBAND &&
              !server->port_attr.lid) {
     fprintf(stderr, "Couldn't get local LID\n");
     exit(EXIT_FAILURE);
@@ -171,6 +171,11 @@ void LCISD_server_init(LCIS_server_t* s)
 
   // query the gid
   server->gid_idx = LCI_IBV_GID_IDX;
+  if (server->gid_idx < 0 &&
+      server->port_attr.link_layer == IBV_LINK_LAYER_ETHERNET) {
+    // User did not explicitly specify the gid to use and we are using RoCE
+    server->gid_idx = select_best_gid_for_roce(server);
+  }
   if (server->gid_idx >= 0) {
     LCI_Log(LCI_LOG_INFO, "ibv", "Use GID index: %d\n", server->gid_idx);
     if (ibv_query_gid(server->dev_ctx, server->dev_port, server->gid_idx,
@@ -352,7 +357,7 @@ void LCISD_endpoint_init(LCIS_server_t server_pp, LCIS_endpoint_t* endpoint_pp,
         exit(EXIT_FAILURE);
       }
     }
-    char wgid[33];
+    char wgid[WIRE_GID_NBYTES + 1];
     memset(wgid, 0, sizeof(wgid));
     gid_to_wire_gid(&endpoint_p->server->gid, wgid);
     // Use this queue pair "i" to connect to rank e.
@@ -375,7 +380,7 @@ void LCISD_endpoint_init(LCIS_server_t server_pp, LCIS_endpoint_t* endpoint_pp,
     uint32_t dest_qpn;
     uint16_t dest_lid;
     union ibv_gid gid;
-    char wgid[33];
+    char wgid[WIRE_GID_NBYTES + 1];
     sscanf(value, "%x:%hx:%s", &dest_qpn, &dest_lid, wgid);
     wire_gid_to_gid(wgid, &gid);
     // Once a queue pair (QP) has receive buffers posted to it, it is now
diff --git a/lct/CMakeLists.txt b/lct/CMakeLists.txt
index ed5b3d85..da9a8cd2 100644
--- a/lct/CMakeLists.txt
+++ b/lct/CMakeLists.txt
@@ -30,7 +30,8 @@ target_sources_relative(
   tbarrier/tbarrier.cpp
   util/thread.cpp
   util/time.cpp
-  util/string.cpp)
+  util/string.cpp
+  util/io.cpp)
 
 target_include_directories(LCT PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 
diff --git a/lct/api/lct.h b/lct/api/lct.h
index 43a59f7d..d9d00c27 100644
--- a/lct/api/lct.h
+++ b/lct/api/lct.h
@@ -203,6 +203,10 @@ LCT_API bool LCT_tbarrier_test(LCT_tbarrier_t tbarrier, int64_t ticket);
 LCT_API void LCT_tbarrier_wait(LCT_tbarrier_t tbarrier, int64_t ticket);
 LCT_API void LCT_tbarrier_arrive_and_wait(LCT_tbarrier_t tbarrier);
 
+// File IO
+LCT_API ssize_t LCT_read_file(char* buffer, size_t max,
+                              const char* filename_fmt, ...);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lct/util/io.cpp b/lct/util/io.cpp
new file mode 100644
index 00000000..3e1b2c38
--- /dev/null
+++ b/lct/util/io.cpp
@@ -0,0 +1,39 @@
+#include <sys/param.h>
+#include <unistd.h>
+#include <stdarg.h>
+#include <fcntl.h>
+#include "lcti.hpp"
+
+ssize_t read_file_vararg(char* buffer, size_t max, const char* filename_fmt,
+                         va_list ap)
+{
+  char filename[MAXPATHLEN];
+  ssize_t read_bytes;
+  int fd;
+
+  memset(buffer, 0, max);
+
+  vsnprintf(filename, MAXPATHLEN, filename_fmt, ap);
+
+  fd = open(filename, O_RDONLY);
+  if (fd < 0) {
+    return -1;
+  }
+
+  read_bytes = read(fd, buffer, max - 1);
+
+  close(fd);
+  return read_bytes;
+}
+
+ssize_t LCT_read_file(char* buffer, size_t max, const char* filename_fmt, ...)
+{
+  ssize_t read_bytes;
+  va_list ap;
+
+  va_start(ap, filename_fmt);
+  read_bytes = read_file_vararg(buffer, max, filename_fmt, ap);
+  va_end(ap);
+
+  return read_bytes;
+}
\ No newline at end of file