Refusing Pings on Core Routers??? A new trend?

Fri Oct 20 02:14:07 UTC 2006

> template response -- I hear is "Well, you can't rely on traceroute
> because of ICMP prioritisation".  When you start to explain how
> traceroute actually works (both ICMP-based and UDP-based (which
> still relies on ICMP responses, of course!)), and that ICMP prio
> should only affect the IP of which the router listens on (and not
> hops beyond or at the dest), most NOCs fire back with another

If I recall well, Cisco GSRs impose low priority and/or limits for all
ICMP traffic flowing thru the box, not just packets to/from router
itself, and there's not a knob to adjust that.

Also of notice is that packets that expire TTL needs some kind of
low-path processing, and will be subject to increased latency or loss
compared to normal ones, and this affects every tool to trace packets
thru the network I've seen.