ICMP ping effecting network flow?

by **Roy L Butler** » Sat, 13 May 2006 08:12:59 GMT

Everyone,

I was told by someone at a systems conference about 10 years ago that if 
you ping a server over the Internet while downloading a file from it, 
your download will take place quicker.  I thought it was bogus then and 
still kind of lean towards that.  I see no difference from some simple 
tests I've tried.  But, perhaps there's something to do with a common 
design of routers and traffic flows that I just don't get.  The guy who 
told me got a knowing nod from someone else and neither were in a 
position to just be pulling legs.  Were they both wrong and just trying 
to sound smart?  Any (real) info would be much appreciated.  It's 
tickled the back of my mind for a long time. :)


Roy

by **Rick Jones** » Sat, 13 May 2006 09:00:56 GMT



I'd chalk it up to leg-pulling.  The only way I could see a ping
helping a transfer would be if it was _just_ enough to help keep the
NICs' interrupt throttles from being too aggressive.  

rick jones
-- 
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

by **ibuprofin** » Sun, 14 May 2006 10:05:07 GMT

On Thu, 11 May 2006, in the Usenet newsgroup comp.os.linux.networking, in




Anecdotal evidence - no observed difference.  Why?  Because the services
have nothing to do with each other.    On the server, the 'ftp' or 'web'
server is an application running at the top of the networking stack. With
most operating systems, 'ping' (ICMP Echo) is a network service that is
part of the networking stack.   At the client side, 'ping' is normally
just another application - which if anything is stealing CPU cycles that
could ordinarily be used for something more useful.


As far as the routers are concerned, it's just another packet. An ICMP
packet _MAY_ be processed at a lower priority than TCP or UDP, because
ICMP is more used as an error, or diagnostic, while the others are
carrying "useful" data.


Why not?   Are you the "boss" that they dare not lie to? Or was their boss
present and would not take kindly to such humor?


Ten years ago - to late to do anything. The right thing to do AT THE TIME
would have been to ask them to explain why they felt this to be true.

        Old guy

by **Roy L Butler** » Sun, 18 Jun 2006 08:16:05 GMT

 > I was told by someone at a systems conference about 10 years ago that if
 > you ping a server over the Internet while downloading a file from it,
 > your download will take place quicker. I thought it was bogus then and
 > still kind of lean towards that. I see no difference from some simple
 > tests I've tried. But, perhaps there's something to do with a common
 > design of routers and traffic flows that I just don't get. The guy who
 > told me got a knowing nod from someone else and neither were in a
 > position to just be pulling legs. Were they both wrong and just trying
 > to sound smart? Any (real) info would be much appreciated. It's
 > tickled the back of my mind for a long time. :)

I've come across documentation that some routers place ICMP traffic in 
their high-priority queue.  Both these guys were heavily certified 
(which I know doesn't always mean qualified), one of them was presenting 
on a loosely-related topic and the other troubleshot national banking 
networks.  My guess is that they might have thought (wrongly?) that 
certain vendors' routers placed all traffic to/from a source address 
issuing echo_requests in such a queue, elevating lower-priority protocols.

I can't remember their names and I agree the time to ask was back then. 
  Unfortunately, I didn't. :(


Roy

by **Constant Meiring** » Sun, 18 Jun 2006 21:04:30 GMT



Ten years ago, pings wouldv'e eaten up your bandwidth... making
downloads slower :)

by **ibuprofin** » Mon, 19 Jun 2006 07:47:07 GMT

n Fri, 16 Jun 2006, in the Usenet newsgroup comp.os.linux.networking, in
article <e6ve3l$mu3$ XXXX@XXXXX.COM >, Roy L Butler wrote:

That still doesn't sound right. Lessee, 10 years ago... On 31 Dec 1995,
the Internet consisted of 1.05 billion IP addresses assigned to 40865
networks world wide (for comparison, the figures earlier this week were
2.318 billion hosts and 73466 IPv4 networks) (Source: RIR Zone files
dated 06/15/2006). If you look at any contemporary documentation
(examples - the man page for the common LBL version of traceroute, or
W. Richard Stevens 'TCP/IP Illustrated Volume 1 - the protocols", Addison
Wesley, ISBN 0-201-63346-9, copyright 1994) you'd see that many
connections over the Internet require at least 6 hops (routers) to get
anywhere - a more common value is over a dozen. In the traceroute man
page, it took 18 hops to go from Lawrence Berkeley Labs (about 45 miles
Southeast of Oakland) to MIT in Boston - and no less than 13 to get from
LBL to a specific server in Berkeley (not more than 50 miles away). The
Stevens book shows similar hop counts as well. It's a bit of a stretch
to think that ten or fif{*filter*} intermediate routers would note a ping
going by from "A" to "B", and therefore remember to pass TCP datagrams
between those hosts with higher priorities. While not very likely at
that era, it is also possible that pings could have been routed over
different intermediate hops compared to TCP.

As far as prioritizing ICMP - can you give some cite? The IP header has
a TOS variable, and one of those is the "minimize delay" flag (see page
29 of RFC0791). These flags have in general been ignored, even back in the
early 1990s (see the Stevens book). RFC1340 (superseded by RFC1700, which
in turn was replaced by on-line databases) and RFC1349 (from July 1992)
specified how these flags were to be set, and the 'Minimize Delay' flag
was only set for 'Telnet/Rlogin', FTP control (but not data), TFTP, SMTP
(command phase, not data) and DNS queries using UDP. These were generally
interactive or setup conditions. There is also a 'Maximize throughput'
flag which was set for bulk data transfers (FTP or SMTP data, DNS zone
transfers).

A lot depends on the certifying organization. Certifications are generally
most useful in getting past the hiring filters set by HR and PHBs. The
actual experience/knowledge would be determined in interviews with the
technical people.

How much memory do you think is in the "average" backbone router? How
much traffic do you think it might see in any given moment? (If you were
traveling by air in the 60s-80s, you probably knew that if you traveled
anywhere in the "South" of the United States (actually meaning Southeast),
you couldn't go ANYWHERE without changing planes in Atlanta. By the mid-90s,
the Internet was a good bit better than that, but there were still a lot of
routes where the path from "A" to "B" went through major hubs like SFO,
Denver, Chicago, and New York - even if you were going from Dallas to
Atlanta.

You might try 'comp.protocols.tcp-ip' or even 'alt.folklore.computers'.
My news server also lists a 'alt.folklore.internet' which might be useful.

Old guy

by **Roy L Butler** » Wed, 21 Jun 2006 02:30:55 GMT

oe Trin wrote:

Thanks for all of the good info. My specific source stating routers may
be configured to treat ICMP echoes as high-priority packets is section
6.5 of _Wide-Area Data Network Performance Engineering_, by Cole &
Ramaswamy (AT&T engineers), written in 2000. They do mention that the
opposite (lower-priority) is common and I can understand how the whole
thing seems even less plausible on a packet-switching architecture...
I'll give up the position of devil's advocate. :)

Roy

by **ibuprofin** » Thu, 22 Jun 2006 11:09:29 GMT

On Mon, 19 Jun 2006, in the Usenet newsgroup comp.os.linux.networking, in




That's certainly possible, but I don't see it being used to treat all
packets to/from the host that pinged with higher (or lower) priority.
This is basically saying that all routers along the way would have to
allocate some memory to remember which host has sourced or replied to
a ping in the last second or so. Probably not a big deal for a stub
router in a home situation, but likely to play merry he!! on a
backbone router connecting a couple of OC-3s (155 Megabit fiber) or
wider.


Sounds good.

        Old guy

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