08-18-2021 08:15 AM
Hello guys,
We have configured cisco switch with igmp version 2 and we got a system that is taking the IP 224.16.17.255 for multicast. Is it a valid IP ending in 255? is it not a broadcast one?
A multicast IP that end in 255 is a valid IP for multicast?
Regards
Jose
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08-18-2021 09:18 AM
I believe that's valid. Rules are different for multicast IPv4 address blocks.
BTW, an unicast IPv4 ending with .255 doesn't have to be a broadcast IP, and conversely, other last octets can be broadcast IPs.
E.g.
10.1.2.255 /23 is a unicast IP
10.1.2.3 /30 is a broadcast IP
08-18-2021 09:28 AM
Hello
thanks for the response but in the unicast as you already showed, the broadcast is defined by the mask however, who define an IP will be broadcast or not in multicast?
08-18-2021 11:42 AM
Perhaps a brief review of terminology might be helpful:
- unicast is an IP packet for which there is a single device as the recipient.
- broadcast is an IP packet for which the recipient is every device.
- multicast is an IP packet for which there is more than 1 recipient but fewer than all.
So there is no concept of broadcast when you are talking about multicast.
08-18-2021 12:16 PM
". . . who define an IP will be broadcast or not in multicast?"
https://datatracker.ietf.org/doc/html/rfc2780#section-4.4.2
https://datatracker.ietf.org/doc/html/rfc3171
https://datatracker.ietf.org/doc/html/rfc5771
08-18-2021 09:18 AM
I believe that's valid. Rules are different for multicast IPv4 address blocks.
BTW, an unicast IPv4 ending with .255 doesn't have to be a broadcast IP, and conversely, other last octets can be broadcast IPs.
E.g.
10.1.2.255 /23 is a unicast IP
10.1.2.3 /30 is a broadcast IP
08-18-2021 09:28 AM
Hello
thanks for the response but in the unicast as you already showed, the broadcast is defined by the mask however, who define an IP will be broadcast or not in multicast?
08-18-2021 11:42 AM
Perhaps a brief review of terminology might be helpful:
- unicast is an IP packet for which there is a single device as the recipient.
- broadcast is an IP packet for which the recipient is every device.
- multicast is an IP packet for which there is more than 1 recipient but fewer than all.
So there is no concept of broadcast when you are talking about multicast.
08-18-2021 01:45 PM
you are right, my back
08-18-2021 12:16 PM
". . . who define an IP will be broadcast or not in multicast?"
https://datatracker.ietf.org/doc/html/rfc2780#section-4.4.2
https://datatracker.ietf.org/doc/html/rfc3171
https://datatracker.ietf.org/doc/html/rfc5771
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