Basic question on multicast address (239.0.0.0-239.255.255.255)

Answered Question
Oct 11th, 2009

For the given multicast address shown below, what would be the subnet mask associated with it? Also, does it make any sense the concept of "broadcast address on a multicast" range? Someone mentioned that broadcast address applies to multicast as well but I am unsure about that.

ip access-list standard ssm-source1

permit 239.254.13.31

Correct Answer by Giuseppe Larosa about 7 years 4 months ago

Hello Marlon,

subnet mask and broadcast address apply to unicast IP addresses only.

Actually each multicast address is indipendent and represents a session or "channel".

the multicast address is divided in groups.

For example addresses like

224.0.0.x

are link local addresses that cannot be routed and are used by routing protocols.

addresses in range

239.0.0.0 - 239.255.255.255

are the equivalent of RFC 1918 unicast addresses:

these are private multicast addresses to be used inside an enterprise not over the internet.

Hope to help

Giuseppe

Correct Answer by Hitesh Vinzoda about 7 years 4 months ago

Hi,

I think of multicast addresses not as IP addresses but rather as Group addresses. Fundamentally Multicast and Broadcast are different things. There is no concept of broadcast within a multicast as such. Multicast addresses are group addresses referred as destination. anyone who wants to receive the Multicast will join the certain group, you can also use 239.255.255.255 as your group address for multicast. As far as subnet address is concerned 239.0.0.0/8 just represents the ip addresse range to be used for private administrative purposes.

Moreover, you never assign multicast addresses on interfaces of network devices, this addresses are always used as destinations.

Regards

Hitesh Vinzoda

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Correct Answer
Hitesh Vinzoda Sun, 10/11/2009 - 22:43

Hi,

I think of multicast addresses not as IP addresses but rather as Group addresses. Fundamentally Multicast and Broadcast are different things. There is no concept of broadcast within a multicast as such. Multicast addresses are group addresses referred as destination. anyone who wants to receive the Multicast will join the certain group, you can also use 239.255.255.255 as your group address for multicast. As far as subnet address is concerned 239.0.0.0/8 just represents the ip addresse range to be used for private administrative purposes.

Moreover, you never assign multicast addresses on interfaces of network devices, this addresses are always used as destinations.

Regards

Hitesh Vinzoda

Correct Answer
Giuseppe Larosa Sun, 10/11/2009 - 22:49

Hello Marlon,

subnet mask and broadcast address apply to unicast IP addresses only.

Actually each multicast address is indipendent and represents a session or "channel".

the multicast address is divided in groups.

For example addresses like

224.0.0.x

are link local addresses that cannot be routed and are used by routing protocols.

addresses in range

239.0.0.0 - 239.255.255.255

are the equivalent of RFC 1918 unicast addresses:

these are private multicast addresses to be used inside an enterprise not over the internet.

Hope to help

Giuseppe

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