packet loss question

[jmkeller at houseofzen.org (jmkeller)]

On 2016-07-07 11:53 PM, William Herrin wrote:
> On Thu, Jul 7, 2016 at 3:52 PM, Ken Chase <math at sizone.org> wrote:
>> ICMP is allowed to be dropped by intervening routers. Someone will 
>> quote an RFC
>> at us shortly.
> 
> Hi Ken,
> 
> That's not correct. Routers might not generate an ICMP time-exceeded
> packet for every packet whose TTL reaches zero, but that's not the
> same thing. Routers dropping ICMP packets in transit would be bad.
> Protocols like TCP depend on path MTU discovery and path MTU discovery
> critically depends on ICMP.
> 
> Regards,
> Bill Herrin


All we are seeing here is control plane filtering by intermediate 
routers.   Unless packet loss numbers start at a router and hops past it 
show the same or higher losses it's not an actual issue with the 
transport path at that hop.   Outside of your own domain of 
administrative control, you can't rely on intermediate routers 
responding to ICMP (either filtered completely or rate limited 
responses).

--
James