On Tue, 24 Sep 2019 at 00:59, Naslund, Steve <[email protected]> wrote:
> Just a tip, but you cannot really determine packet loss on an MPLS network > with a traceroute. The nodes between the provider edge routers may not even > represent your real path. Also, provider routers within their network will > be handling pings much differently than they handle your actual traffic. The > pings require processing whereas your MPLS traffic will be label switched. > Much different performance. This is not MPSL specific, equally in natively forwarded you can only determine packet loss for the ultimate host, this is because TTL==1 packets are punted to software processing typically, and such punting is heavily rate-limited to conserve control-plane resources, so reply may not come. This isn't something devices have to do, but it is something they do, NPU based devices could reply to TTL==1 from NPU at wire-rate to fix this problem, and is only a matter of someone asking their vendor to do that. The MPLS speciality is that RTT may be far-end RTT for whole transit, because LSR may not know how to send reply, LSR may only have IGP, so LSR may need to send TTL unreachable message to far-end LER, which will then reply back to sender, causing each step to represent far-end LER RTT. This is not happening in the described traceroute. Hope this helps. -- ++ytti
