IPv6 Solicited node multicast

[Justin Westover]

I don't quite understand the way IPv6 RS and RA works. I know that Neighbor Discovery Protocol (ND) is the replacement in the IPv6 world for ARP, I just don't understand how it works. So from what I understand, when you enable ipv6 on an interface, it will automatically assign itself a link local address (e.g. FF8O::213:19FF:FE7E:5004) at this point I believe that it uses this Link Local address as the source address when performing a RS (router solicitation). What I don't understand is the multicast part of this, who does the solicitation go to? What multicast group is this solicitation sent to and does everything on the local link receive this solicitation? I understand that when a router or host creates the link local address, they also join a multicast group for their link local address so they can listen for soliciations. I just don't understand the whole RS process haha.

So let's say I have two routers that are directly connected to one another. Each creates a link local using EUI-64, then each router will join a multicast group for the link local it created. I create a Globally unique ipv6 address on the two connected interfaces of the routers and the last 64 bits are created using EUI-64, the first 64 bits are 2000:0:0:1::/64 and the interface addresses are 2000:0:0:1::1/64 and the other is 2000:0:0:1::2/64. So now when I ping from 2000:0:0:1::1 to 2000:0:0:1::2 there obviously needs to be a RS, at this point the RS would do what exactly? I think I have everything down up until this process, please someone help fill in the blanks here!!

[cadet alain]

Hi,

RS= Router solicitation sent to allRouters on the link which is FF02::2 asking for a  /64 prefix so the interface can be  autoconfigured by using stateless autoconfig( host part = EUI-64). The reply is a unicast RA advertising the prefix along with other parameters.

On a router you can configure an IPv6 address in different ways:

- ipv6 address 2001:CC1E::1/64   we are specifying the host part

- ipv6 address autoconfig   we are using stateless autoconfig as explained above

- ipv6 address  2001:CC1E::/64  eui-64   we are specifying the prefix part and the host part will be derived from MAC

ARP has been replaced by ND: each time you configure an IPv6 address you join the sollicited-node multicast for this IPv6 address.To populate neighbour cache(same as IPv4 arp cache) the host is sending a NS to this sollicited-node multicast and the reply is a unicast NA.This multicast address is also used for DAD( duplicate address detection) using the same type of mechanism.

Regards.

Alain.

[lgijssel]

First of all, the router joins several multicast groups:

Global unicast address(es):

    FC00:A:B:0:C601:DFF:FE28:0, subnet is FC00:A:B::/64 [EUI]

  Joined group address(es):

    FF02::1

    FF02::2

    FF02::A

    FF02::1:FF28:0

A new end node coming online will first try to aquire a link-local address.

It will then use this address to send an RS to gather information about subnets and routers on the link.

This RS is sent to the "all routers" multicast group. (FF02::2)

Responses are sent by all routers receiving the RS. These responses are called RA's.

When sent in response to an RS, the RA is sent to the link-local address sourcing the RS.

In addition to this, routers send periodic RA's every 200s.

These unsolicited RA's are sent to the "All nodes"multicast address. (FF02::1)

regards,

Leo