IPv6 extension headers

Hop-by-Hop Options
Routers will look at it
Routing
Source routes
Fragment
Fragmentation, ONLY at originating node
Destination Options
Pass info to final destination
IPsec (AH, ESP)

Header chain
Header parsing code becomes somewhat different from IPv4

IPv6(nxt=TCP) TCP payload
IPv6(nxt=routing) Routing(nxt=TCP) TCP payload
IPv6(nxt=fragment) Fragment(nxt=TCP) TCP payload