How to join multiple multicast groups on one interface - ruby

Question

The Ruby version I have available is 1.8.7 and can't be upgraded as it is part of standard image that is used on all the companies Linux servers at this time and anything I do needs to be able to run on all of these servers without issue (I'm hoping though this won't be an issue)
The project I am doing is to recreate an application that currently runs on Windows on a Linux server. The application takes a list of multicast groups and interfaces and attempts to join the groups and then listens for any data (doesn't matter what) reporting whether it could join and the data was there. It helps us in our environment prove out network connectivity prior to deployment of actual software on to the server. The data that it will be receiving will be binary encoded financial information from an exchange so I don't need to output (hence the commented out line and the output) I just need to check it is available to the server.
I have read up online and found bits and pieces of code that I have cobbled together into a small version of this where it joins 1 multicast group bound to 1 interface and listens for data for a period of time reporting whether any data was received.
I then wanted to add a second multicast group and this is where my understanding is lacking in how to achieve this. My code is as follows:
#!/usr/bin/ruby
require 'socket'
require 'ipaddr'
require 'timeout'
MCAST_GROUP_A =
{
:addr => '233.54.12.111',
:port => 26477,
:bindaddr => '172.31.230.156'
}
MCAST_GROUP_B =
{
:addr => '233.54.12.111',
:port => 18170,
:bindaddr => '172.31.230.156'
}
ipA = IPAddr.new(MCAST_GROUP_A[:addr]).hton + IPAddr.new(MCAST_GROUP_A[:bindaddr]).hton
ipB = IPAddr.new(MCAST_GROUP_B[:addr]).hton + IPAddr.new(MCAST_GROUP_B[:bindaddr]).hton
begin
sockA = UDPSocket.open
sockA.setsockopt Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, ipA
sockA.setsockopt Socket::IPPROTO_IP, Socket::IP_ADD_MEMBERSHIP, ipB
sockA.bind Socket::INADDR_ANY, MCAST_GROUP_A[:port]
sockA.bind Socket::INADDR_ANY, MCAST_GROUP_B[:port]
timeoutSeconds = 10
Timeout.timeout(timeoutSeconds) do
msg, info = sockA.recvfrom(1024)
#puts "MSG: #{msg} from #{info[2]} (#{info[3]})/#{info[1]} len #{msg.size}"
puts "MSG: <garbled> from #{info[2]} (#{info[3]})/#{info[1]} len #{msg.size}"
end
rescue Timeout::Error
puts "Nothing received connection timedout\n"
ensure
sockA.close
end
The error I get when I run this is:
[root#dt1d-ddncche21a ~]# ./UDPServer.rb
./UDPServer.rb:35:in `setsockopt': Address already in use (Errno::EADDRINUSE)
from ./UDPServer.rb:35
So that's where I am at and could really do with firstly pointers as to what is wrong (hopefully with an update to the code) and then once I this example working the next step will to be add a second interface into the mix to listen to again multiple multicast groups,

Answer 1

Ok so I followed the advice given to bind to the interface first for each port and then add members for each of the multicast groups I want to listen to and this has resolved this particular issue and moved me on to the next issue I have. The next issue I will raise as a new topic.