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

[benpicco]

Contribution description

When using gnrc_border_router on native the build system will take care of creating a TAP interface and running UHCP/DHCPv6 on it.

This is not always the desired behavior.
e.g. when a TAP bridge was created with a real interface to provide an uplink to native or ethos, we actually want to use that instead of creating a new one.

We then also want to use the real DHCPv6 server instead of starting our own one.

This adds the REUSE_TAP=1 option to skip network setup and just use the provided TAP interface as the uplink.

Testing procedure

• create a bridge with your Ethernet adapter (interface name may vary)

  sudo dist/tools/tapsetup/tapsetup -u eno1
  

• start the border router with the tap uplink

  make REUSE_TAP=1 -C examples/gnrc_border_router all term
  

• the border router should receive a global address and can reach internet hosts

Iface  6  HWaddr: 7A:37:FC:7D:1A:AF 
          L2-PDU:1500  MTU:1492  HL:255  RTR  
          Source address length: 6
          Link type: wired
          inet6 addr: fe80::7837:fcff:fe7d:1aaf  scope: link  VAL
          inet6 addr: 2001:9e8:140f:fc00:7837:fcff:fe7d:1aaf  scope: global  VAL
          inet6 group: ff02::2
          inet6 group: ff02::1
          inet6 group: ff02::1:ff7d:1aaf
          
Iface  7  HWaddr: 44:28  Channel: 26  NID: 0x23  PHY: O-QPSK 
          Long HWaddr: AA:78:BF:FD:E1:06:C4:28 
           State: IDLE 
          ACK_REQ  L2-PDU:102  MTU:1280  HL:64  RTR  
          RTR_ADV  6LO  IPHC  
          Source address length: 8
          Link type: wireless
          inet6 addr: fe80::a878:bffd:e106:c428  scope: link  VAL
          inet6 addr: 2001:9e8:140f:fcf4:a878:bffd:e106:c428  scope: global  VAL
          inet6 group: ff02::2
          inet6 group: ff02::1
          inet6 group: ff02::1:ff06:c428
          
> ping riot-os.org
12 bytes from 2001:67c:254:b0b0::1: icmp_seq=0 ttl=60 time=25.104 ms
12 bytes from 2001:67c:254:b0b0::1: icmp_seq=1 ttl=60 time=147.904 ms
12 bytes from 2001:67c:254:b0b0::1: icmp_seq=2 ttl=60 time=50.646 ms

--- riot-os.org PING statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 25.104/74.551/147.904 ms

• Bonus: virtual 802.15.4 nodes can also reach the internet

  make USE_ZEP=1 -C examples/gnrc_networking all term
  

Iface  7  HWaddr: 61:B3  Channel: 26  NID: 0x23  PHY: O-QPSK 
          Long HWaddr: 5E:AF:98:F2:44:49:E1:B3 
           State: IDLE 
          ACK_REQ  L2-PDU:102  MTU:1280  HL:64  RTR  
          RTR_ADV  6LO  IPHC  
          Source address length: 8
          Link type: wireless
          inet6 addr: fe80::5caf:98f2:4449:e1b3  scope: link  VAL
          inet6 addr: 2001:9e8:140f:fcf4:5caf:98f2:4449:e1b3  scope: global  VAL
          inet6 group: ff02::2
          inet6 group: ff02::1
          inet6 group: ff02::1:ff49:e1b3
          inet6 group: ff02::1a
          
          Statistics for Layer 2
            RX packets 3  bytes 246
            TX packets 3 (Multicast: 2)  bytes 0
            TX succeeded 3 errors 0
          Statistics for IPv6
            RX packets 2  bytes 248
            TX packets 3 (Multicast: 2)  bytes 210
            TX succeeded 3 errors 0

> ping riot-os.org
12 bytes from 2001:67c:254:b0b0::1: icmp_seq=0 ttl=59 rssi=0 dBm time=24.319 ms
12 bytes from 2001:67c:254:b0b0::1: icmp_seq=1 ttl=59 rssi=0 dBm time=23.516 ms
12 bytes from 2001:67c:254:b0b0::1: icmp_seq=2 ttl=59 rssi=0 dBm time=147.707 ms

--- riot-os.org PING statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 23.516/65.180/147.707 ms

Issues/PRs references

[riot-ci]

Murdock results

✔️ PASSED

299b5ac examples/gnrc_border_router: honor $TAP setting

Success	Failures	Total	Runtime
2000	0	2000	06m:58s

Artifacts

• Documentation preview

This only reflects a subset of all builds from https://ci-prod.riot-os.org. Please refer to https://ci.riot-os.org for a complete build for now.

[OlegHahm]

The proposed works as expected, but I cannot oversee all potential unwanted side effects. And I realized that the tapsetup script has an unwanted side effect when tearing down a bridge with a connected uplink.

[benpicco]

This just adds another option to the existing scripts. It should not have any side effects if not used.

[benpicco]

Thank you!