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Why does EXOS not see my multicast receiver ?

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TitleWhy does EXOS not see my multicast receiver ?
Question
Why does EXOS not see my multicast subscriber ?
Environment
  • EXOS >= 15.7.x
  • IGMP join/report
Answer
In EXOS 15.7 a fix is implemented (xos0056880) that only allows IGMP packets with a TTL=1.
In previous EXOS version every IGMP packet was excepted, no matter how high the TTL was.

If your device sends an IGMP packet with a TTL higher than 1 EXOS will not accept the packet as valid IGMP packet and not take action.
This is completely according to the RFC 3376.
 
RFC 3376 Section 4, Page 7
 
4. Message Formats
   IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol
   number of 2.  Every IGMP message described in this document is sent
   with an IP Time-to-Live of 1, IP Precedence of Internetwork Control
   (e.g., Type of Service 0xc0), and carries an IP Router Alert option
   [RFC-2113] in its IP header.
 
      <snip>
 
   Unrecognized message types MUST be silently ignored.  Other message
   types may be used by newer versions or extensions of IGMP, by
   multicast routing protocols, or for other uses.


 
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