Comment by lxgr
13 hours ago
> They absolutely don't. Routers are layer 3 devices;
Idealized routers are, yes.
Actual IP paths these days usually involve at least one NAT, and these will absolutely throw away anything other than TCP, UDP, and if you're lucky ICMP.
See nearby comment about terminology. Either we're discussing odd IP protocols, then the devices you're describing aren't just "routers" (and particularly what you're describing is not part of a "router"), or we're not discussing IP protocols, then we're not having this thread.
And note the GP talked about "intermediate routers". That's the ones in a telco service site or datacenter by my book.