examples/gnrc_border_router: add option to re-use existing TAP interface

dist/tools/zep_dispatch/start_network.sh

@@ -25,7 +25,9 @@ remove_tap() {
 
 cleanup() {
     echo "Cleaning up..."
-    remove_tap
+    if [ "${CREATE_TAP}" -eq 1 ]; then
+        remove_tap
+    fi
     if [ -n "${UHCPD_PID}" ]; then
         kill "${UHCPD_PID}"
     fi
@@ -64,6 +66,13 @@ start_zep_dispatch() {
     ZEP_DISPATCH_PID=$!
 }
 
+if [ "$1" = "-c" ] || [ "$1" = "--create-tap" ]; then
+    CREATE_TAP=1
+    shift 1
+else
+    CREATE_TAP=0
+fi
+
 if [ "$1" = "-d" ] || [ "$1" = "--use-dhcpv6" ]; then
     USE_DHCPV6=1
     shift 1
@@ -101,7 +110,9 @@ for TAP in "$@"; do :; done
 
 trap "cleanup" INT QUIT TERM EXIT
 
-create_tap
+if [ ${CREATE_TAP} -eq 1 ]; then
+    create_tap
+fi
 
 if [ ${USE_ZEP_DISPATCH} -eq 1 ]; then
     start_zep_dispatch

examples/gnrc_border_router/Makefile

@@ -43,7 +43,7 @@ USEMODULE += ps
 #USEMODULE += gnrc_ipv6_nib_dns     # include RDNSS option handling
 
 # When using a regular network uplink we should use DHCPv6
-ifneq (,$(filter cdc-ecm wifi ethernet,$(UPLINK)))
+ifneq (,$(filter cdc-ecm wifi ethernet,$(UPLINK)) $(REUSE_TAP))
   PREFIX_CONF ?= dhcpv6
 else
   PREFIX_CONF ?= uhcp

examples/gnrc_border_router/Makefile.native.conf

@@ -9,10 +9,14 @@ CFLAGS += -DASYNC_READ_NUMOF=$(shell expr $(ZEP_DEVICES) + 1)
 # Set CFLAGS if not being set via Kconfig
 CFLAGS += $(if $(CONFIG_KCONFIG_MODULE_DHCPV6),,-DCONFIG_DHCPV6_CLIENT_PFX_LEASE_MAX=$(ZEP_DEVICES))
 
-ifeq (dhcpv6,$(PREFIX_CONF))
-  FLAGS_EXTRAS += --use-dhcpv6
-else ifeq (auto_subnets,$(PREFIX_CONF))
-  FLAGS_EXTRAS += --use-radvd
+# create a new TAP interface if not re-using an existing one
+ifneq (1, $(REUSE_TAP))
+  FLAGS_EXTRAS += --create-tap
+  ifeq (dhcpv6,$(PREFIX_CONF))
+    FLAGS_EXTRAS += --use-dhcpv6
+  else ifeq (auto_subnets,$(PREFIX_CONF))
+    FLAGS_EXTRAS += --use-radvd
+  endif
 endif
 
 # enable the ZEP dispatcher

examples/gnrc_border_router/README.md

@@ -44,6 +44,21 @@ credentials. You can alternatively edit the `Makefile`.
 Currently, `wifi` requires an esp8266 or esp32 for the border router and will default
 to using `esp_now` for the downstream interface.
 
+### Connection sharing with host
+
+If the host (Linux) computer has an IPv6 uplink that can be shard with the RIOT border
+router to provide it with an uplink.
+
+This requires the host network to be bridged with the TAP network by connecting it to
+the TAP bridge:
+
+    sudo dist/tools/tapsetup/tapsetup -u eno1
+
+where `eno1` is the host's uplink interface.
+
+Then specify `REUSE_TAP=1` when building / running the border router application.
+This works with both `native` and the `ethos` uplink.
+
 ## Requirements
 This functionality works only on Linux machines.
 macOS support will be added in the future (lack of native `tap` interface).