[outages] Level3 packet loss in Washingon, DC

[Nimrod Levy]

It's not so much that they block ICMP (tho some do), it's more that the
router does not prioritize processing packets with an expired TTL. Doing so
requires generating an ICMP TTL Expired packet in reply. The original
packet could be anything. Many traceroutes use UDP or ICMP and have options
for TCP as the initial packet.

My favorite traceroutes as problem reports are the ones in a word document
where they've pasted a screenshot of a command shell.


On Sat, May 11, 2019 at 6:47 AM Mike Bolitho via Outages <
outages at outages.org> wrote:

> Anyone on this list who hasn't read this needs to. I used to work
> break/fix at Level 3. I cannot tell you how many times otherwise smart
> engineers misunderstood or misread traceroute results. Seems like
> PingPlotter results are generally used as the "gotcha" evidence. Most ISPs
> rate limit and full on block ICMP.
>
>
> Read this
>>
>>
>> https://www.nanog.org/meetings/nanog47/presentations/Sunday/RAS_Traceroute_N47_Sun.pdf
>>
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