On Tue, 24 Sep 2019 at 00:59, Naslund, Steve <SNaslund@medline.com> 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