The IPv6 Travesty that is Cogent's refusal to peer Hurricane Electric - and how to solve it

multihop bgp means that you don't have synchronised ethernet carrier
status between the provider and customer routers. This in turn means
that if there's an intermediate connectivity problem, bgp will need to
time out before it notices and reroutes. During this period, traffic
will be black-holed. This is a crock.

Not many customers can support this.

And even if they did, not all implementations are executed in hardware
on either side of the BGP session.