On 8/24/25 10:40, Saku Ytti via NANOG wrote:
Infact even internally in our AS, we would almost certainly loop if we didn't do MPLS, because due to specific policy and TE reasons we filter advertisements differently in_iBGP-IN_, this is also kind of big no-no, and if we did do IP lookup in core transit I cannot at all guarantee we wouldn't loop, but because we can guarantee that the edge decision is honored all the way to the other edge, we can get away with it.
This practical matter regularly comes up when we're doing BGP extensions. We need to design the protocol to be safe on a hop by hop basis so that iBGP safely works - especially with reflectors. You can get away with all sorts of murder if you promise you tunnel edge to edge. -- Jeff