[tex-live] www.tug.org unreachable

Denis Bitouzé dbitouze at wanadoo.fr
Mon Dec 18 20:03:07 CET 2017

Le 18/12/17 à 13h20, Michael Shell a écrit :

> 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,

That's what I'm doing every evening.

> even disconnect it from the wall for an hour or so.

Not disconnected but powered down every night, is it enough?

> Try forcing a change in your router's IP address.  You
> can find info by doing a search for:
> how reset router IP address

Sigh... I read on my ISP forums that either my IP is fix and it cannot
be changed, or it is dynamic and I shouldn't have this problem since
such a long time.

> 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/

Sigh... beyond my skills.

> 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.

I see.

> 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

  │ ╭─bitouze at drums-bis ~/
  │ ╰─➤  ip link list
  │ 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
  │     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
  │ 2: enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
  │     link/ether 50:9a:4c:31:ce:9d brd ff:ff:ff:ff:ff:ff
  │ 3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default qlen 1000
  │     link/ether 52:54:00:52:29:68 brd ff:ff:ff:ff:ff:ff
  │ 4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq_codel master virbr0 state DOWN mode DEFAULT group default qlen 1000
  │     link/ether 52:54:00:52:29:68 brd ff:ff:ff:ff:ff:ff

> 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:

Except loopback, seems to be OK, isn't it?

> ifconfig wlan0 mtu 1450

  │ ╭─root at drums-bis /home/bitouze  
  │ ╰─➤  ifconfig enp0s31f6: mtu 1450

but that didn't help.

> 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

Well, I'm not sure: what are the commands to run before?

> 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

Sigh... beyond my skills.

I blindly run the commands above but no success for my problem.

> 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 my router and/or my ISP were wrong, I probably encountered this
problem with other sites, isn't it?

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

Of course.

Many thanks for such a detailed message!


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