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70 lines
3.4 KiB
Markdown
70 lines
3.4 KiB
Markdown
#MIP TCP / IP stack over pcap
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This example allows to use Mongoose's MIP built-in TCP/IP stack on systems
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that support pcap API, i.e. have libpcap library installed. The application
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opens an interface and uses `pcap_next_ex()` for reading packets from the
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interface, and `pcap_inject()` to write packets to the interface.
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NOTE: depending on the libcap implementation, the injected packets may
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or may not be looped back to the interface's TCP/IP stack. If they are
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not looped back, then it is necessary to create a separate interface that
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is bridged to the target interface - see MacOS example below.
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## MacOS setup
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MacOS has support for `feth` (fake ethernet) interfaces. One can create a pair
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of `feth` interfaces and interlink them. Once a `feth` interface is assigned
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a peer and an IP address, anything that gets injected to it, appears on a
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peer interface and vice versa.
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```sh
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$ sudo ifconfig feth0 create
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$ sudo ifconfig feth1 create
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$ sudo ifconfig feth1 peer feth 0 # Link two fake ethernet ifaces together
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$ sudo ifconfig feth1 10.10 # Assign 10.0.0.10 to feth1
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$ sudo ifconfig feth0 up
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$ sudo ifconfig feth1 up
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```
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Now we have two Ethernet interfaces, `feth0` and `feth1`, interlinked and
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active. On your Mac, go to "System Preferences" / Sharing, enable "Internet
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Sharing" and choose "Thunderbolt bridge". This enables DHCP on the `bridge0`
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interface, which is bridge for all Thunderbolt devices, and adds necessary
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routes to the WiFi interface. On my system it gets `192.168.2.1` IP address,
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and serves `192.168.2/24` net. We should add one of our fake interfaces to
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this bridge:
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```sh
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$ sudo ifconfig bridge0 addm feth1
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```
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We cat start an example using the `feth0`:
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```sh
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$ make -C examples/mip-pcap/ clean all ARGS="-i feth0"
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...
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2386718 3 mip.c:279:arp_cache_add ARP cache: added 0xc0a80201 @ 36:77:4d:be:e0:80
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2386718 2 mip.c:300:onstatechange READY, IP: 192.168.2.17
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```
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The diagram of the setup is below:
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```
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┌──────────► 192.168.2.1 bridge0
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│ routing DHCP │
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│ ┌──────────────────┴──────────────────┐
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▼ │ │ 192.168.2.17
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│ ┌─────────┐ fake ethernet pair ┌─────────┐
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192.168.0.10 │ │ feth1 ├────────────┬───────┤ feth0 │
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┌─────────┐ │ └─────────┘ │ └────┬────┘
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│ en0 │ │ │ │
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└────┬────┘ │ ┌─────────┐ ┌─────────┐ ┌─────────┐ │ │
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│ │ │ en1 │ │ en2 │ │ en3 │ │ mip-pcap
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│ └────┬────┘ └────┬────┘ └────┬────┘ │
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WiFi │ │ │ │ │
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└──────┼───────────┼───────────┼──────┘
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│ │ │ │
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▼
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Internets Thunderbolt Ethernet
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```
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