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  1. Hi Diana,

    Glad to hear you like it!

    There’s not really a short answer to your question. Technically, ND doesn’t require MLD to work.

    IPv6 ND uses multicast and the solicited node multicast addresses.

    Using multicast instead of broadcast sounds effective but in reality, your ND traffic is probably still broadcasted since your L2 switches don’t know where to forward the multicast traffic to.

    To improve this, you could enable MLD snooping on the switches. Your hosts will have to report what they want to receive through MLD and then the switch will be able to deliver multicast traffic only on the required interfaces.

    This sounds great but in reality, it doesn’t work. Each host will have a unique solicited multicast address so if you have 1000 hosts then your switch has to keep track of 1000 multicast groups. Depending on the switch, it might be unable to do this.

    It’s best to keep MLD snooping disabled, your NICs will drop multicast traffic that they are not interested in.


  2. Hello Rahul

    Whenever you configure an interface to function as an IPv6 interface, it automatically sends out NS messages.
    This will occur even BEFORE any IPv6 addresses have been configured. You can see from your capture and from your CLI that you have posted, that both R1 and R2 have link-local addresses of FE80::C001:8FFF:FEEF:0 and FE80::C001:8FFF:FEF7:0 respectively.

    As for the NA message, those are sent under two conditions: The first is as a response to an NS and the second when there is a change in the link-layer address of a node on a local link. When this occurs, the destination address for the neighbor advertisement is the all-nodes multicast address.

    Let’s take a look at the NAs from your output. Looking at packet number 2 you have:
    Source fe80::c001:8fff:feef:0
    Destination ff02::1
    The destination is the all-nodes multicast address. So this NA was a result of a change on the link, specifically, the automatic configuration of the link-local address.

    Similarly, packet number 8 is an NA with the following characteristics:
    Source 2001::1
    Destination ff02::1
    Notice again, the destination is an all-nodes multicast address, therefore this NA has also been sent because of a change on the link-layer address. We can see the change that was made from the Source which is now 2001::1 which is the address you configured on the interface.

    Network advertisements 16 and 22 can also be analysed in the same way, and you can see that those are the corresponding NAs from R2.

    So you can see that an IPv6 interface will always send NS messages, will send NA messages as a response to NS messages OR will send NA messages whenever there is a change to the link address.

    I hope this has been helpful!


  3. @castrojuanj
    Hello Juan,
    I hope you are doing well,
    I have labed your question and took a packet capture to see if I can help you understand NDP better.

    First off a link-local address is configured in two ways.

    1. The administrator specifies the link-local address to be used
    2. The local router uses eui-64 to generate the proper IP address for link-local use

    Now if you have a unique local and global unicast IP address assigned to the same interface and it receives an RS, it will the respond with an address for both unique local and global unicast addresses. So no the router only needs to go through the RS/RA process once to get IP addresses, and the auto config command only needs to run on the remote router once.

    Also I have included a pcap file that will let you see what I did in wireshark.

    NDP example.pcapng (5.2 KB)

    I hope this helps!

  4. Yes, off course it helps !

    Thank you so much for your time and reply. Have a nice weekend.

  5. you state this twice. Once here and once above. The first time you stated it I was not sure as I just thought on it briefly. Not liking the answer but then you state it again here so I thought on it a few moments more.

    It then started to make sense I understood why the question was asked however but the answer was so basic it was hard to accept.

    Basically, anytime you go somewhere there is normally a method a destination and its the same here with the answer. This entire teaching component is about how to find the Layer 2 as this has replaced ARP.

    Everyone that asked the question including myself over complicated it because the reality is the answer is so simple.

    You have a destination in this format the destination is described by IP addresses. So if you know the destination then you know the IP address which then you know the multicast node and you also know it uses the last 5 hex of the IP address so you know what the specific multicast node is to basically request the layer two.

    Once you have the layer two just like ipv4 you still have an adjancey table with all the MACs associated with the IPs.

    The question is then not what is the destination because now we know that but why do you want that destination now that is something to think deeper on.

    You may not really want the destination of the connected router but perhaps only be traveling through it to another router to another destination.

    I think it would be nice to have illustration setup for IPV6 like those old ipv4 summaries where it tells you how to travel from Point A to Point E and it progresses through switching and a couple of subnets there would be less questions and it would be much more clear as I always turned to those on ipv4 when I forgot something or became confused and needed to resettle my mind.

    those obviously took you through a few technologies as you followed the packet but it was really nice to have and kept the world right side up. I would love to have one of those for ipv6 :slight_smile:

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