ccna ipv6 question

[daniel4579329]

Hi
im learning for the ccna and i have a couple of questions about ipv6

1. why do we need all these type of multicast and especially why do we need Link-local multicast address

2. what is the scope and why we need them and are they address that only on a packet (can they be on an interface /port )

thanks for the help (:

[balaji.bandi]

This is more of learning question with Instructor to explain - not technical community

here is for your learning :

https://study-ccna.com/what-is-ipv6/

https://www.ccnablog.com/ipv6-internet-protocol-version-6/

here is the learning community :

https://learningnetwork.cisco.com/s/

[Martin L · Accepted solution]

why do we need Link-local multicast address

L3 Broadcast does not exists in IPv6, which is good thing; it caused a lots sort of problems in IPv4, so they decided to "replace" B-cast with M-cast.  Replacing B-cast with M-cast meant M-cast must be adopted to provide a wider variety of usage; in addition to Ipv4 M-cast usage.  Besides, B-cast is not exactly eliminated or removed; it is replaced with all-node multicast IPv6 address. 

To better match Ipv4 B-cast with new Ipv6 M-cast, they came out with the idea of using Scopes: Global, Site-local, Link-local, interface-local.  This Scope filed in M-cast address tells us ID or a type of M-cast but also how far it can reach or propagate (tells us range of address).  

Link-local scope is what closely matching old IPv4 interface B-cast to new M-cast; In IPv4, router breaks B-cast scope; each interface creates new B-cast reach.  In IPv6, each router interface means different M-cast scope (local scope); Here is where multicast address like All OSPF or Rip or EIGRP routers are used; just they are adopted to IPv6 format.

Example of Site-local is all DHCP serves M-cast address. 

Regards, ML
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[daniel4579329]

 can they (the multicast types) be on an interface /port  or they only a destination on a packet

[Giuseppe Larosa]

Hello @daniel4579329 ,

as it happens in IPv4 multicast addresses are only valid as destination addresses and not as source IP address.

So no router interface or host can have a multicast address directly configured on it.

However, as we say a router interface or an host interface can be a receiver interested in receiving traffic from one or more multicast addressees.

Hope to help

Giuseppe

[daniel4579329]

didnt fully understand the  answer (about ipv6)

[Giuseppe Larosa · Accepted solution]

Hello @daniel4579329 ,

IPv6 multicast addresses cannot be assigned to a router interface or a host NIC.

They can only appear as destination addresses in IPv6 packets.

This is exactly the same as it happens in Ipv4.

A router interface / host NIC can be a member of a multicast group = a receiver for Group G but address G cannot be assigned to it.

I hope is more clear now

Hope to help

Giuseppe