Can there be any extension header before Neighbor Solicitation Payload The IPv6 payload may like the following: IPv6 Header -> ExtHeader -> ... -> UpperLayer Header I use Scapy to make a packet such that: IPv6 -> Hop-by-Hop-Option -> Neighbor Solicitation [1] However from Sniffer, I don't see the Neighbor Advertisement response. So I try with this kind of packet: IPv6 -> Neighbor Solicitation [2]. Then It's work! Just wondering, the packet format I make in [1] is invalid? So the opposite station doesn't honor it?? Thanks

The other station might not understand your extension headers, in which case it can not reply to them. But in general extension headers are allowed in all packets, even Neighbour Discovery.