67 lines
2.9 KiB
Markdown
67 lines
2.9 KiB
Markdown
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# UDP Multicast Example
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This example shows how to use the IPV4 & IPV6 UDP multicast features via the BSD-style sockets interface.
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## Behaviour
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The behaviour of the example is:
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* Listens to specified multicast addresses (one IPV4 and/or one IPV6).
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* Print any UDP packets received as ASCII text.
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* If no packets are received it will periodicially (after 2.5 seconds) send its own plaintext packet(s) to the multicast address(es).
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## Configuration
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The "Example Configuration" menu "make menuconfig" allows you to configure the details of the example:
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* WiFi SSD & Password
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* IP Mode: IPV4 & IPV6 dual, IPV4 only, or IPv6 only.
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* Multicast addresses for IPV4 and/or IPV6.
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* Enable multicast socket loopback (ie should the socket receive its own multicast transmissions.)
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* Change the interface to add the multicast group on (default interface, or WiFi STA interface.) Both methods are valid.
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## Implementation Details
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In IPV4 & IPV6 dual mode, an IPV6 socket is created and the "dual mode" options described in [RFC4038](https://tools.ietf.org/html/rfc4038) are used to bind it to the default address for both IPV4 & IPV6 and join both the configured IPV4 & IPV6 multicast groups. Otherwise, a single socket of the appropriate type is created.
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The socket is always bound to the default address, so it will also receive unicast packets. If you only want to receive multicast packets for a particular address, `bind()` to that multicast address instead.
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## Host Tools
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There are many host-side tools which can be used to interact with the UDP multicast example. One command line tool is [socat](http://www.dest-unreach.org/socat/) which can send and receive many kinds of packets.
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### Send IPV4 multicast via socat
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```
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echo "Hi there, IPv4!" | socat STDIO UDP4-DATAGRAM:232.10.11.12:3333,ip-multicast-if=(host_ip_addr)
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```
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Replace `232.10.11.12:3333` with the IPV4 multicast address and port, and `(host_ip_addr)` with the host's IP address (used to find the interface to send the multicast packet on.)
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### Receive IPV4 multicast via socat
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```
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socat STDIO UDP4-RECVFROM:3333,ip-add-membership=232.10.11.12:(host_ip_addr)
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```
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Replace `:3333` and `232.10.11.12` with the port and IPV4 multicast address, respectively. Replace `(host_ip_addr)` with the host IP address, used to find the interface to listen on.
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(The `,ip-add-membership=...` clause may not be necessary, depending on your network configuration.)
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### Send IPV6 multicast via socat
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```
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echo "Hi there, IPV6!" | socat STDIO UDP6-DATAGRAM:[ff02::fc]:3333
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```
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Replace `[ff02::fc]:3333` with the IPV6 multicast address and port, respectively.
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### Receive IPV6 multicast via socat
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At time of writing this is not possible without patching socat. Use a different tool or programming language to receive IPV6 multicast packets.
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## About Examples
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See the README.md file in the upper level 'examples' directory for general information about examples.
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