[tex-live] www.tug.org unreachable

[Michael Shell]

On Mon, 18 Dec 2017 17:20:00 +0100
Denis Bitouzé <dbitouze at wanadoo.fr> wrote:

> WDYT?

>From all the information provided, it sure does look like a problem with
the TUG hosting company or ISP.

Now, that said, trying disconnecting your internet connection - power
down and reset your modem/router, even disconnect it from the wall
for an hour or so. Try forcing a change in your router's IP address.
You can find info by doing a search for:

how reset router IP address


The above said, if I had to bet, my money would go on that the problem
you are seeing is the result of a MTU/fragmentation/ECN router bug
issue within an ISP network. See:

https://superuser.com/questions/386708/cant-access-some-websites-possible-mtu-issue-on-the-router
http://blog.glinskiy.com/2009/02/packetization-layer-path-mtu-discovery.html
https://fitzcarraldoblog.wordpress.com/2010/11/30/why-cant-i-access-a-specific-web-site/

In short, something is "special" about the packets your system is
generating, not necessarily "wrong", just "rather unique" and this
is triggering a bug in a router downstream. Of course, the network
provider doesn't believe it is their problem because, "Hey, our
stuff works for everyone else, so we *must* be OK."

Under Linux/Unix, you can do a 

ip link list

to see the Maximum Transmit Unit (MTU, aka send packet size) each
of your network interfaces is using. The MTU on the outgoing interface
should not be over 1500. You should try setting it lower, to say, 1450:

ifconfig wlan0 mtu 1450

You can also try enabling Packetization Layer Path MTU Discovery
(PLPMD) and see if that has any effect:
 
echo 2 > /proc/sys/net/ipv4/tcp_mtu_probing

Another source of such problems is buggy routers that do not
support Explicit Congestion Notification (ECN) which is controlled
under the Linux kernel via

/proc/sys/net/ipv4/tcp_ecn

e.g., 
cat /proc/sys/net/ipv4/tcp_ecn
echo 0 > /proc/sys/net/ipv4/tcp_ecn

see for example:

http://bloat.bufferbloat.narkive.com/BtoUTYXS/ecn-blocking-router-found


Anyway, I think the line of reasoning above is on the right track,
even if not perfectly spot on with regard to the name of the
specific network parameter that is triggering the bug in your
case.

If you find the cause, please do let us (as well as the ISP) know
who is the offender. 


   Cheers,

   Mike Shell