mongoose/examples/mip-pcap/README.md

#MIP TCP / IP stack over pcap

This example allows to use Mongoose's MIP built-in TCP/IP stack on systems that support pcap API, i.e. have libpcap library installed. The application opens an interface and uses pcap_next_ex() for reading packets from the interface, and pcap_inject() to write packets to the interface.

NOTE: depending on the libcap implementation, the injected packets may or may not be looped back to the interface's TCP/IP stack. If they are not looped back, then it is necessary to create a separate interface that is bridged to the target interface - see MacOS example below.

MacOS setup

MacOS has support for feth (fake ethernet) interfaces. One can create a pair of feth interfaces and interlink them. Once a feth interface is assigned a peer and an IP address, anything that gets injected to it, appears on a peer interface and vice versa.

$ sudo ifconfig feth0 create
$ sudo ifconfig feth1 create
$ sudo ifconfig feth1 peer feth 0     # Link two fake ethernet ifaces together
$ sudo ifconfig feth1 10.10           # Assign 10.0.0.10 to feth1
$ sudo ifconfig feth0 up
$ sudo ifconfig feth1 up

Now we have two Ethernet interfaces, feth0 and feth1, interlinked and active. On your Mac, go to "System Preferences" / Sharing, enable "Internet Sharing" and choose "Thunderbolt bridge". This enables DHCP on the bridge0 interface, which is bridge for all Thunderbolt devices, and adds necessary routes to the WiFi interface. On my system it gets 192.168.2.1 IP address, and serves 192.168.2/24 net. We should add one of our fake interfaces to this bridge:

$ sudo ifconfig bridge0 addm feth1

We cat start an example using the feth0:

$ make -C examples/mip-pcap/ clean all ARGS="-i feth0" 
...
2386718 3 mip.c:279:arp_cache_add       ARP cache: added 0xc0a80201 @ 36:77:4d:be:e0:80
2386718 2 mip.c:300:onstatechange       READY, IP: 192.168.2.17

The diagram of the setup is below:

      ┌──────────►   192.168.2.1     bridge0
      │ routing      DHCP               │
      │              ┌──────────────────┴──────────────────┐
      ▼              │                                     │       192.168.2.17
                     │              ┌─────────┐ fake ethernet pair ┌─────────┐
192.168.0.10         │              │  feth1  ├────────────┬───────┤  feth0  │
┌─────────┐          │              └─────────┘            │       └────┬────┘
│   en0   │          │                                     │            │
└────┬────┘          │ ┌─────────┐ ┌─────────┐ ┌─────────┐ │            │
     │               │ │   en1   │ │   en2   │ │   en3   │ │         mip-pcap
                     │ └────┬────┘ └────┬────┘ └────┬────┘ │
    WiFi             │      │           │           │      │
                     └──────┼───────────┼───────────┼──────┘
     │                      │           │           │
     ▼
 Internets                      Thunderbolt Ethernet