Re: Linux ping flood on localhost

Anthony Towns (aj@azure.humbug.org.au)
Sat, 17 Apr 1999 00:19:17 +1000


On Fri, Apr 16, 1999 at 08:44:07AM -0400, Richard B. Johnson wrote:
> On Fri, 16 Apr 1999, Tigran Aivazian wrote:
> > >Ummm, If I remember correctly it was a bug in the ping program itself and
> > > not in the kernel.
> > > Just upgrade your version of ping.
> > Yes, we know it is an FAQ and everybody knows the correct answer "get the
> > latest ping" but, even the best Linux distributions (you know who you
> > are!) still come with the ping(8) that says 95% packet loss on lo.

FWIW, Debian's current stable release (slink, 2.1) ships with a working
ping.

(Now, if that's not the *lamest* piece of evangelism I've ever seen... ;)

> I think the latest ping will produce 90% packet loss on a flood to
> localhost. This was some kind of 'feature' (a side-effect) introduced
> around 2.2.x (Alan responded to this). As I understand it, ICMP replies
> are delayed by a HZ, so the maximum response-rate is 100/second. Ping
> flood tries 1000/second so you lose the flood-game.

] [aj@sapphire ~/project/netbase]$ sudo ping -c 10000 -f localhost
] Password:
] PING localhost (127.0.0.1) from 127.0.0.1 : 56 data bytes
] .
] --- localhost ping statistics ---
] 10000 packets transmitted, 10000 packets received, 0% packet loss
] round-trip min/avg/max = 0.0/0.1/53.8 ms

IIRC, the real problem is that when listening on a raw socket you now
get to see your outgoing pings as well as the incoming responses, so a
new ping gets sent off every time it sends a ping as well as every time
it receives a ping, which just leads to confusion all around.

Cheers,
aj

-- 
Anthony Towns <aj@humbug.org.au> <http://azure.humbug.org.au/~aj/>
I don't speak for anyone save myself. PGP encrypted mail preferred.

``Like the ski resort of girls looking for husbands and husbands looking for girls, the situation is not as symmetrical as it might seem.''

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