IPv6 Duplicate address found - NA reponse

If an NS is sent and a host on the link finds it is using the tentative IPv6 address described in the NS, it responds with an NA. Doyle's TCP/IP Routing Vol. 1 states that "If a node receives an NS and the target address matches one of its assigned addresses, it sends an NA with the Target Address and the destination address set to the tentative address."The first host has used a source address of ::/128 so if the NA sets the destination address as the tentative address, how does it reach the first device (the one who sent the NS for DAD)?

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wave

Is the NA being broadcast at layer 2?

SteveO86

The destination of the NA from NodeB would be the address of the device that send the NS (NodeA)

In your case the packet would be sent to it's own address. Not sure when you would see this situation though considering though.

http://www.ietf.org/rfc/rfc2461.txt -Section 4.3 & 4.4 NA/NS

NA's are sent as Multicast, under section 4.3

wave

Thanks for your reply Steve. Just to clarify:

Node A sends an NS and node B receives it and sees that it owns the IPv6 address that node A is trying to claim. Doyle says that when Node A sends its NS it uses the solicited node multicast address, and places the IPv6 address it is doing the DAD for in the target field as a "tentative address". The source address of that packet is ::/128

So node B receives the NS and his response is to fire an NA back. Doyle says this uses the tentative IPv6 address (which A wants) as the destination and target address. It does not say that this NA is sent to the all nodes multicast address FF02::1

The RFC states "Destination Address For solicited advertisements, the Source Address of an invoking Neighbor Solicitation or, if the solicitation's Source Address is the unspecified address, the all-nodes multicast address."

Doyle states "The destination address is either the source address of the packet containing the NS to which the NA is sent in response, or the all-nodes multicast address FF02::1"

So in theory, the NA should use a destination address of ::/128 - my guess is that would result in it being forwarded to all nodes?

SteveO86

wave wrote: »

The RFC states "Destination Address For solicited advertisements, the Source Address of an invoking Neighbor Solicitation or, if the solicitation's Source Address is the unspecified address, the all-nodes multicast address."

Doyle states "The destination address is either the source address of the packet containing the NS to which the NA is sent in response, or the all-nodes multicast address FF02::1"

So in theory, the NA should use a destination address of ::/128 - my guess is that would result in it being forwarded to all nodes?

RFC says one things, Doyle says the same or it uses the all multicast nodes address. Might need to lab that one up to see which one Cisco devices really do.

SteveO86

Just labbed this up.. Score one for Doyle.

The NS packet sends its destination as the link local address it will be using.

The other router assigned that same link local address responds back with a source of it's link local and a destination of FF02::1

I've attached screen shots of both packets notice the layer 2 source is different so you know they are coming from different hosts.

NS Packet.jpg

NA packet.jpg