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Can NDP (Neighbor Discovery Protocol) neighbor solicitation/advertisement be used with IPv4 in their "mapped" IPv6 form? I wrote a simple ARP/NDP example and tried using NDP for both IPv4 and IPv6, but no devices I tried seemed to respond.

The relevant RFC does not say much about IPv4 so I am thinking that perhaps NDP just isn't backward compaible. However, there also aren't many examples of programmatic NDP use so I may have done something wrong.

Extra credit question if anybody knows: is there a way to get the target MAC address from a NDP Advertisement other than just reading it from the ethernet header? ARP has the MAC in the payload too but I am not seeing something similar for NDP.

Trevor Gross
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  • First, remember that IPv4-Mapped IPv6 addresses are not allowed to be used on a network, as explained in the _[IANA IPv6 Special-Purpose Address Registry](https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml)_. Notice that they cannot be used as source or destination addresses, cannot be forwarded or globally routable, and they are reserved by IP itself They are not actual IPv6 addresses, only a representation of IPv4 addresses in the IPv6 format in order to have a common address store, e.g. database. – Ron Maupin Aug 26 '23 at 14:15
  • NDP goes beyond what IPv4 can do: "_The IPv6 Neighbor Discovery protocol corresponds to a combination of the IPv4 protocols..._" and "_The Neighbor Discovery protocol provides a multitude of improvements over the IPv4 set of protocols..._" NDP uses special IPv6 multicast addresses (solicited-node) that are not available in IPv4 multicast, and IPv4 routers do not send RAs the way IPv6 routers do. – Ron Maupin Aug 26 '23 at 14:23

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