subject:"Re\: Problema para navegar"

Re: Problema para navegar

2001-11-28 Por tema Francesc Lumbierres




>Tienes activado ECN en el kernel? ECN (Explicit Congestion
>Notification) es una opci?n de compilaci?n en los kernel 2.4.x... y
>puede hacer que NO veas determinadas p?ginas... Te hago copy & paste...


Si ... efectivamente. Ultimamente estoy haciendo pruebas con filtrado y 
nat y habia activado varias opciones en la parte de "Networking options" 
del kernel y esta opcion (ECN) precisamente la tenia activada. Me he 
dado cuenta al "quitar" todas las opciones innecesarias, pero sabia cual 
era la que fastidiaba el asunto. Muchas, muchas Gracias.

Re: Problema para navegar ...

2001-11-28 Por tema Javier Miguel Rodriguez

LUMBIERRES wrote:

Saludos a la lista ...Tengo un problema que ya comienza a tocarme las narices.Ultimamente, hay algunas paginas web que no hay forma de entrar, es más,no me contestan (timeout) y lo curioso es que me pasa con todos losnavegadores en Linux (Mozilla, Konqueror, Netscape, etc) en cambio, yhay que joderse, si funcionan en Windows+explorer. En concreto laspaginas son por ejemplo www.ibm.com, www.nvidia.com, www.infojobs.com yalgunas más. Hay algo que se me escapa?.

¿Tienes activado ECN en el kernel? ECN (Explicit Congestion Notification)
es una opción de compilación en los kernel 2.4.x... y puede hacer que NO
veas determinadas páginas... Te hago copy & paste...

Your upgrade to kernel 2.4.0, or anything later, went perfectly, or
so you thought. You downloaded all the files you needed, built the kernel,
upgraded modutils, and booted. Voila! Working system! So you played around
a bit, decided it was working fine, and went back to your normal work.
Around noontime you decided to check your stock portfolio on E-Trade
or to look at the financial news on the NASDAQ web site. "Gee!" you thought
as your browser failed to connect, "It's amazing that both of these major
financial sites are down at the same time!" So you went back to what you
were doing. A couple of hours later they were still unreachable, and you
began to wonder if the problem was really at their end, or at yours.
Since the only thing you changed was the kernel, you rebooted under
your old kernel and tried NASDAQ. It was working fine now. Boot the 2.4.x
kernel and it's gone again. What's going on here?
The answer is that Linux is once again on the cutting edge of networking
technology with its implementation of an experimental protocol called Explicit
Congestion Notification, or ECN. The technical details of ECN are described
in a Request for Comment (RFC) document published by the Internet Engineering
Task Force (IETF).
RFC 2481 is the relevant document, with
RFC 2884 providing additional information. (
http://www.ietf.org/).
In layman's terms, ECN is a way to improve the speed of the Internet
for everyone by allowing hosts or routers to specifically notify one another
when there is congestion due to heavy traffic. With the existing TCP/IP standards,
the only way to detect congestion was that routers would drop packets when
they had no bandwidth available. These packets would be automatically retransmitted
by the sending host, but the host would (presumably) notice that packets
were being dropped and would decrease its transmission rate.
ECN changes all that by allowing routers to notify hosts that the packet
they just received experienced congestion delays as it wended its way across
the Internet. The presumption is that the hosts become active partners with
the Internet infrastructure, helping to manage the overall traffic pattern
by making more reasonable requests of the infrastructure.
The problem with Linux 2.4.x and ECN is that not all of the existing
routers and other devices on the Internet can support ECN. In fact, some
older devices actually treat ECN packets as invalid, and discard them altogether.
This explains the problem with NASDAQ and E-Trade's web sites, both of which
(as of a few days ago) did not support ECN packets. There are other sites
with this problem as well, and in fact Internet.com had to upgrade some of
its own equipment several months ago as a result of this new protocol.
Eventually, the network infrastructure will be updated so that this
new protocol (currently experimental) is supported everywhere, but what can
a Linux user do about the problem in the meantime? The good news is that
there is an easy workaround, and it doesn't involve staying with the 2.2.x
kernel.
In configuring the 2.4.x kernels, you can disable ECN by turning off
the CONFIG_INET_ECN option (titled "IP: TCP Explicit Congestion Notification"
in the interactive configurators) before building the kernel. This completely
removes ECN support from the kernel, but of course you then have no way to
test with it to see when you might turn it back on.
Another, perhaps simpler, approach is to use the sysctl feature of the
/proc virtual filesystem to turn off ECN at runtime. Executing this command:

echo "0" > /proc/sys/net/ipv4/tcp_ecn
will turn off ECN support until the next reboot, while replacing "0"
with "1" in the above command will turn ECN back on. You can safely put this
command in your rc.local or other bootup script, or make it part of your
SysV init processing.
With Explicit Congestion Notification turned off, Linux 2.4.x kernels
have no trouble accessing NASDAQ, E-Trade, or other sites that don't yet
support ECN. Once the infrastructure catches up, use of ECN by Linux (and
other) clients will hopefully bring better Internet speed to all of us.