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Webcast-Catalyst9k
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ipv6 and broadcast

hi

i have usually heard that IPv6 resolved the problem of broadcast

however today i read that the "neighbor discovery" ICMP message replaced the ARP request

but this "neighbor discovery" is using the multicast as destination address

and if i m not wrong the L2 switch will treat these multicast as broadcast , i mean it will send it to all active ports !

so how did IPv6 eliminates broadcast? we just changed the name ! but at the end the neighbor discovery message will reach all ports ! isn't it ?

thanks

3 REPLIES

Re: ipv6 and broadcast

Hello. We have to differentiate two different protocols : ethernet and IPv6.

What you said is correct. IPv6 doesn't have broadcast , instead of that IPv6 uses multicasts.

On the other hand Ethernet does support both broadcasts and multicasts, but Ethernet in order to recognize multicasts it needs extra configuration (IGMP snooping to work with IPv4 multicast and MLD snooping to work with IPv6 multicast).

So when you send an IPv6 multicast it will be encapsulated by default within a "broadcast" Ethernet frame and will be sent out all switchports, unless you configure MLD snooping.

Please rate if it helps. Kind regards

Purple

ipv6 and broadcast

Hi,

a switch can tell if a frame is unicast or broadcast/multicast by looking at the I/G bit in the first octet.

What IGMP snooping and MLD snooping do is alleviate the flooding of multicast that the switch does by default.

Regards.

Alain

Don't forget to rate helpful posts.
New Member

ipv6 and broadcast

Hi Alain,

Your answer gets close to a post of mine ealier.

Can you enable MLD snooping, even when no MSFC is part as a L3 interface on that specific IPv6 vlan ?
(eg. The FWSM is provding the L3 functionality)

Thx!

Wim

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