[e2e] What's wrong with this picture?

Jeroen Massar jeroen at unfix.org
Mon Sep 7 05:57:55 PDT 2009

sthaug at nethelp.no wrote:
>> That is not what I meant. Just think of the case where there is a nice
>> ISP involved, or for that matter several, who are doing "QoS" and
>> prioritizes ICMP a lot lower than TCP... you do know that all bittorrent
>> is evil and that everything over port 80 is 'good' don't you? :)
> Do you know of *any* ISPs that explicitly prioritize ICMP a lot lower
> than TCP for traffic *through* the ISP's routers?

I know several ISPs with heavily misconfigured "QoS" or rather
"prioritization" setups. They tend to configure "TCP port 80" (unless it
goes to some streaming site like Youtube) as good traffic, and thus
high-prio that traffic, everything else is dropped in the bad bucket.
ICMP is generally forgotten or directly classified as 'only used for
DDoS' and thus make it very low-priority. It might sound logical for the
person who configures it, but it is actually not...

> Note that this is
> different from ICMP to/from the router itself.

That is generally because of the hardware doing queuing and depending on
platform because the CPU of the box has to handle it instead of just
forwarding the packets. As the latencies where traceroute, the packets
would hit the router itself and it would have to handle it.
(if TTL=0 oeeeh, it is me ;)


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