instruction: Write Docker code for networking
output: ```bash
  $ docker container attach alpine4
  
  # ping -c 2 alpine1
  
  PING alpine1 (172.18.0.2): 56 data bytes
  64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.074 ms
  64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.082 ms
  
  --- alpine1 ping statistics ---
  2 packets transmitted, 2 packets received, 0% packet loss
  round-trip min/avg/max = 0.074/0.078/0.082 ms
  
  # ping -c 2 alpine2
  
  PING alpine2 (172.18.0.3): 56 data bytes
  64 bytes from 172.18.0.3: seq=0 ttl=64 time=0.075 ms
  64 bytes from 172.18.0.3: seq=1 ttl=64 time=0.080 ms
  
  --- alpine2 ping statistics ---
  2 packets transmitted, 2 packets received, 0% packet loss
  round-trip min/avg/max = 0.075/0.077/0.080 ms
  
  # ping -c 2 alpine3
  ping: bad address 'alpine3'
  
  # ping -c 2 172.17.0.2
  
  PING 172.17.0.2 (172.17.0.2): 56 data bytes
  64 bytes from 172.17.0.2: seq=0 ttl=64 time=0.089 ms
  64 bytes from 172.17.0.2: seq=1 ttl=64 time=0.075 ms
  
  --- 172.17.0.2 ping statistics ---
  2 packets transmitted, 2 packets received, 0% packet loss
  round-trip min/avg/max = 0.075/0.082/0.089 ms
  
  # ping -c 2 alpine4
  
  PING alpine4 (172.18.0.4): 56 data bytes
  64 bytes from 172.18.0.4: seq=0 ttl=64 time=0.033 ms
  64 bytes from 172.18.0.4: seq=1 ttl=64 time=0.064 ms
  
  --- alpine4 ping statistics ---
  2 packets transmitted, 2 packets received, 0% packet loss
  round-trip min/avg/max = 0.033/0.048/0.064 ms
  ```