* Baldur Norddahl: > Den 26. sep. 2016 18.02 skrev "Mike Hammett" <na...@ics-il.net>: >> >> The only asymmetric routing broken is when the source isn't in public > Internet route-able space. That just leaves those multi-ISP WAN routers > that NAT it. > > Some of our IP transits implement filtering. All of our transits assigned > /30 subnets on the transit ports from their own range (the alternate would > have be to ask us to supply the /30 from our pool). > > Our provider edge router will send back ICMP packets using the interface > address from the interface that received the original packet. It will then > route the packet using our normal routing table. > > This means we can receive some packet on transit port A and then route out > a ICMP response on port B using the interface address from port A. But > transit B filters this ICMP packet because it has a source address > belonging to transit A.
Interesting. But this looks like a feature request for the router vendor, and not like an issue with BCP 38 filtering as such. > From this follows that BCP38 can break things like traceroute and path MTU > discovery in what is a very common setup. That doesn't follow. In order to break PMTUD, you also need an MTU drop. Is that a common configuration for routers in points in the network where this would matter?
