IPv6-03 IPv6 Neighbor Discovery, Multicast and DAD

These three topics all work together. Join me as we take a look at the concepts, implementation and verifications of these IPv6 protocols.

Category:

Education

Tags:

• IPv6 Neighbor discovery
• Cisco IPv6
• Duplicate Address Detection
• IPv6 multicast

[kasperd42]

Nice video. This video taught me something I did not already know about IPv6, that does not happen often. After watching, I still have one question. How does the switch know which ports a multicast packet needs to be send on? If it sends it on all ports, you don't save much bandwidth.

[Keith6783]

@kasperd42

Thanks for the comments. In a worse case scenario, lets say the frame gets forwarded to all ports in the VLAN. Every device would see the L2 destination address, and if not interested could discard it, without further de-encapsulation.

To your point, regarding bandwidth not being saved, you are right on. To correct that, we could use MLD snooping on the switch, and then only send the frames to the members of the group who had joined.

Best wishes,

Keith

[viiskendkuuskend]

It's probably same in the IPv4, but: What does happen when the response form the box with the same IPv6 address that you wish to use on yours doesn't reach back in time. The time which a host spends on listening and waiting for a reply from group multicast seems quite random(and short).

You could argue and say that it's enough in "networking time" and I'm sure it is, but there can be quite a few complications - let's just cut the wire for a second for example.

[HenryHoneyBadger]

I like your videos Keith but that woosh sound always scares this shit out of me.

[5xYkz]

I can't believe it, I'm finally understanding IPv6.

[ThePaperboy9]

Well... I'm working on my CCNP studies and finally entering the world of IPv6 for the first time. Oh maaaan lol. It's like learning how devices communicate all over again. It's so different! The multicasts are pretty cool though. IPv4 seems like child's play now haha!

[Keith6783]

@Yugandhar635

In the neighbor solicitation, in as part of the ICMP payload, the requester includes his source MAC address that the other device can use. It is also possible, that the other host could issue it's own neighbor solicitation, even though the original one had the MAC in it.

Keith

[Yugandhar635]

@Keith6783

Thanks for your reply.

Finally If R1 wants to know hostA MAC Addr it sends NS using Solicited Node Multicast address, with Dest L2 Addr being equal to 33:33:ff + last 24 bits of that solicited node address.

Now when HostA has to reply back with NA to R1 and HostA doesn't have the L2 Addr of R1 then how it will respond back to R1.What L2 Dest address will HostA use in its reply to R1 as both the hosts are unaware of each other's L2 Address.

[Keith6783]

@Yugandhar635

For the solicited node multicast address, the last 24 bits of the IP address are used as the last 1/2 of the destination MAC address for that solicited node. For other multicast, it uses the last 32 bits of the IP address for the multicast group as the last 32 bits of the destination MAC address for that multicast group.

Thanks for the post!

Keith

[Yugandhar635]

@Keith6783

When we ping to FF02::1 the dest MAC is 33:33:00:00:00:01. Now Similary when we ping to solicited Multicast node like FF02:1:FFAA:AAAA what is the dest MAC address in the IPV6 Packet.