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49 lines
1.2 KiB
Markdown
49 lines
1.2 KiB
Markdown
---
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title: "Multicast Receive Script"
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date: 2020-11-18T10:09:15-05:00
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draft: false
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tags: []
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---
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I use `socat` to debug mutlicast traffic, though the syntax for it is complicated to learn. Here is the command that I normally use to debug multicast traffic.
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```bash
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socat UDP4-RECVFROM:"$port",ip-add-membership="$multicast_address":0.0.0.0,fork -
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```
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This says to:
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- Listen to UDP traffic from `$port`.
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- Subscribe to `$multicast_address`.
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- `0.0.0.0` means to do it from the interface that matches the routing table for the multicast address.
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- The rest makes it print the traffic to standard out.
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To make life easier I created a little script called `mrecv` that takes a multicast address and port and forms the socat command for me.
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```bash
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#!/bin/bash
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show_usage() {
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echo "Usage: mrecv [multicast_address] [port]"
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exit 1
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}
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contains_help_flag() {
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if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
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return 0
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fi
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return 1
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}
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if [ "$#" -ne 2 ] ||
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contains_help_flag "$1" ||
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contains_help_flag "$2"; then
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show_usage
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fi
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multicast_address="$1"
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port="$2"
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socat UDP4-RECVFROM:"$port",ip-add-membership="$multicast_address":0.0.0.0,fork -
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```
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