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NDP - Solicited node multicast group

Answered Question
Feb 29th, 2012
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Hello everyone,

I can`t understand the process of layer3 to layer2 address resolution in IPv6.

In order to make a Layer-2 (eg. Ethernet) delivery, it needs to know the target host's hardware address (eg. "Ethernet MAC address"). But in order to do this, it must first determine which hardware address to send it to. To do this, an IPv6 host will construct the Solicited-node Multicast Address related to the target address.


The IPv6 solicited-node multicast address has the prefix FF02:0:0:0:0:1:FF00:0000/104 concatenated with the 24 low-order bits of a corresponding IPv6 address.


For the target with address

fe80::2aa:ff:fe28:9c5a

solicated node multicast address would become

ff02::1:ff28:9c5a.















1- For example when a host has two unicast address 2001::AB:CDEA and link local fe80:2aa:ff:fe28:9c5a on its interface, does it join the associated solicited-node multicast group for every address to which it is assigned or only for link local adress?.

2- If only for link local address, how will the source device know the link local address of target to borrow last 24 bit? Can I use global address for target address while layer3 to layer2 address resolution?

3- Does all ND functions use link local address? Must a node know all neighbours link local address? If yes, what mechanism are needed to learn link local address of neighbours.

All replies will be appreciated.



Thanks

Gokmen...

Correct Answer by cadet alain about 5 years 5 months ago

Hi,

1) a node always joins the sollicited-node multicast for every IPv6 address it has configured on the ethernet interface including the link-local.

2) this destination multicast address is used for neighbour sollicitation( equivalent of ARP in IPv4) and DAD( duplicate address detection) which is the equivalent of Gratuitous ARP request in IPv4.

So when you want to communicate with a destination IPv6 address it must first do a NS to find out the L2 address and it will send it to the sollicited-node multicast corresponding to the IPv6 destination address

when the node is configured with an IPv6 address it will verify if it is unique by sending a NS to its sollicited-node multicast and if it receives a reply it considers the address is not unique.


3) no it must know how to send to link-local if it wants to communicate with link-local only


http://www.ietf.org/rfc/rfc2461.txt


Regards.


Alain

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Correct Answer
cadet alain Wed, 02/29/2012 - 11:27
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Hi,

1) a node always joins the sollicited-node multicast for every IPv6 address it has configured on the ethernet interface including the link-local.

2) this destination multicast address is used for neighbour sollicitation( equivalent of ARP in IPv4) and DAD( duplicate address detection) which is the equivalent of Gratuitous ARP request in IPv4.

So when you want to communicate with a destination IPv6 address it must first do a NS to find out the L2 address and it will send it to the sollicited-node multicast corresponding to the IPv6 destination address

when the node is configured with an IPv6 address it will verify if it is unique by sending a NS to its sollicited-node multicast and if it receives a reply it considers the address is not unique.


3) no it must know how to send to link-local if it wants to communicate with link-local only


http://www.ietf.org/rfc/rfc2461.txt


Regards.


Alain

furkan023 Wed, 02/29/2012 - 23:03
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Thanks alot Alain. It seems simpler than I thought.


Regards.

Gokmen

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