[92921] in North American Network Operators' Group
Re: Refusing Pings on Core Routers??? A new trend?
daemon@ATHENA.MIT.EDU (Rubens Kuhl Jr.)
Thu Oct 19 22:14:59 2006
Date: Thu, 19 Oct 2006 23:14:07 -0300
From: "Rubens Kuhl Jr." <rubensk@gmail.com>
To: nanog@merit.edu
In-Reply-To: <20061020002049.GA76294@icarus.home.lan>
Errors-To: owner-nanog@merit.edu
> 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.
