Comment by Dagger2
2 days ago
https://datatracker.ietf.org/doc/html/rfc2460#section-4:
With one exception, extension headers are not examined or processed
by any node along a packet's delivery path, until the packet reaches
the node (or each of the set of nodes, in the case of multicast)
identified in the Destination Address field of the IPv6 header.
That seems like the opposite of needing to know all possible extension headers in order to route a packet.
Again, in practice the packets with _any_ IPv6 extension headers are unusable when traversing the public Internet: https://blog.apnic.net/2022/10/13/ipv6-extension-headers-rev...
The issue is that the extension headers can be used for nefarious purposes, such as hop-by-hop routing. So your fast hardware-based border routers might be EH-agnostic and transmit packets to your core network. And then a helpful Linux box that implements all of IPv6 in software would reflect the traffic right past your firewall.
Implementing the EHs in hardware is expensive, as you need to do conditional checks. So routers just drop them.
That really seems more like a problem with the people dropping the packets than with the packet design itself.
How else would you do it? Forcing every packet to reserve space for every possible option (including all future ones) seems obviously worse.