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Rock

2013-Feb-28 17:12 UTC

[CentOS] What can I do to UNDERSTAND why I can't reach centos.org (but everyone else can)?

What can I do to UNDERSTAND why, periodically, I can't reach 
www.centos.org (but everyone else can)?

Every few months, http://www.centos.org just drops off for me
and for me only. It's not the web site, because I can reach it
via a proxy (e.g., TOR browser bundle) and other tests show it
to be alive (e.g., http://www.downforeveryoneorjustme.com/centos.org
or http://traceroute.monitis.com).

But, for me, I just can't reach it by any means. 

Mike Easter kindly determined "centos.org does not echo ICMP or UDP
pings, only TCP, and its associated netblock level3 doesn't echo UDP, 
but does echo ICMP and TCP."

But, for me, this is what a traceroute returned just now on Centos:

$ traceroute www.centos.org 
... early hops removed ... 
16  ae-6-6.ebr2.LosAngeles1.Level3.net (4.69.148.201)  211.850 ms
ae-3-3.ebr3.Dallas1.Level3.net (4.69.132.78)  205.221 ms
ae-6-6.ebr2.LosAngeles1.Level3.net (4.69.148.201)  207.392 ms
17  ae-3-3.ebr3.Dallas1.Level3.net (4.69.132.78)  128.453 ms
ae-73-73.csw2.Dallas1.Level3.net (4.69.151.145)  160.451 ms
ae-93-93.csw4.Dallas1.Level3.net (4.69.151.169)  160.437 ms
18  ae-83-83.csw3.Dallas1.Level3.net (4.69.151.157)  165.923 ms
ae-1-60.edge3.Dallas1.Level3.net (4.69.145.8)  165.920 ms  178.414 ms
19  LAYERED-TEC.edge3.Dallas1.Level3.net (4.71.170.6)  241.537 ms  244.324 ms
ae-3-80.edge3.Dallas1.Level3.net (4.69.145.136)  244.318 ms
20  * LAYERED-TEC.edge3.Dallas1.Level3.net (4.71.170.6)  244.291 ms  244.250 ms
21  * * *
22  * * *
23  * * *
24  * * *
25  * * *
26  * * *
27  * * *
28  * * *
29  * * *
30  * * *

Here is a screenshot (modified to remove early hops) using mtr:
 $ mtr www.centos.org
   http://www2.picturepush.com/photo/a/12303130/img/12303130.png

My related questions are:
1. What can I do (on Centos) to UNDERSTAND this problem?
2. Why does this problem happen every few months to me (and to just me)?
3. How can the net be this arbitrary and still work?

m.roth at 5-cent.us

2013-Feb-28 18:40 UTC

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[CentOS] What can I do to UNDERSTAND why I can't reach centos.org (but everyone else can)?

Rock wrote:> What can I do to UNDERSTAND why, periodically, I can't reach
> www.centos.org (but everyone else can)?
>
> Every few months, http://www.centos.org just drops off for me
> and for me only. It's not the web site, because I can reach it
> via a proxy (e.g., TOR browser bundle) and other tests show it
> to be alive (e.g., http://www.downforeveryoneorjustme.com/centos.org
> or http://traceroute.monitis.com).
>
> But, for me, I just can't reach it by any means.
Could you define "me"? Are you using this at home, or at work? What
kind
of connection? If this is work, are you paying for a fix
IP?>
> Mike Easter kindly determined "centos.org does not echo ICMP or UDP
> pings, only TCP, and its associated netblock level3 doesn't echo UDP,
> but does echo ICMP and TCP."
>
> But, for me, this is what a traceroute returned just now on Centos:
>
> $ traceroute www.centos.org
> ... early hops removed ...
> 16  ae-6-6.ebr2.LosAngeles1.Level3.net (4.69.148.201)  211.850 ms
> ae-3-3.ebr3.Dallas1.Level3.net (4.69.132.78)  205.221 ms
> ae-6-6.ebr2.LosAngeles1.Level3.net (4.69.148.201)  207.392 ms
> 17  ae-3-3.ebr3.Dallas1.Level3.net (4.69.132.78)  128.453 ms
> ae-73-73.csw2.Dallas1.Level3.net (4.69.151.145)  160.451 ms
> ae-93-93.csw4.Dallas1.Level3.net (4.69.151.169)  160.437 ms
> 18  ae-83-83.csw3.Dallas1.Level3.net (4.69.151.157)  165.923 ms
> ae-1-60.edge3.Dallas1.Level3.net (4.69.145.8)  165.920 ms  178.414 ms
> 19  LAYERED-TEC.edge3.Dallas1.Level3.net (4.71.170.6)  241.537 ms  244.324
> ms ae-3-80.edge3.Dallas1.Level3.net (4.69.145.136)  244.318 ms
> 20  * LAYERED-TEC.edge3.Dallas1.Level3.net (4.71.170.6)  244.291 ms
> 244.250 ms
Interesting. I get to 20 (except for me it's 15), and www.centos.org is
the next hop (16). Now, I *do* have fat pipes and good connections (this
is a US fed gov't site), but still....
<snip>> My related questions are:
> 1. What can I do (on Centos) to UNDERSTAND this problem?
> 2. Why does this problem happen every few months to me (and to just me)?
> 3. How can the net be this arbitrary and still work?
Have you spoken to your ISP? When you try the traceroute, and it fails,
have you tried other well-known locations, like google.com, or
slashdot.org?

Also, have you compared the contents of /etc/resolv.conf now, and again
when centos.org isn't visible?

Sounds like either a firewall, spam, or nameserver issue.

     mark

John R Pierce

2013-Feb-28 19:06 UTC

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[CentOS] What can I do to UNDERSTAND why I can't reach centos.org (but everyone else can)?

On 2/28/2013 9:12 AM, Rock wrote:> $ traceroutewww.centos.org  
> ... early hops removed ...
> 16  ae-6-6.ebr2.LosAngeles1.Level3.net (4.69.148.201)  211.850 ms
ae-3-3.ebr3.Dallas1.Level3.net (4.69.132.78)  205.221 ms
> ...
thats a rather high hop count to get that far.  I see...

$ traceroute www.centos.org
traceroute to www.centos.org (72.232.194.162), 30 hops max, 40 byte packets
  1  ge-0-0-1-414.er2.sjc1.got.net (207.111.214.242)  0.511 ms  0.440 
ms  0.462 ms
  2  ge-0-0-1-10.cr1.scz1.got.net (207.111.198.49)  3.961 ms  3.956 ms  
4.193 ms
  3  ge-1-3-0-745.cr1.sfo1.got.net (207.111.219.131)  7.796 ms  7.784 
ms  7.765 ms
  4  vlan114.car2.SanFrancisco1.Level3.net (4.53.130.89)  28.162 ms 
28.165 ms  29.320 ms
  5  ae-2-4.bar2.SanFrancisco1.Level3.net (4.69.133.158)  8.636 ms 8.621 
ms  8.594 ms
  6  ae-6-6.ebr2.SanJose1.Level3.net (4.69.140.154)  50.823 ms 50.664 
ms  50.917 ms
  7  ae-2-2.ebr2.SanJose5.Level3.net (4.69.148.141)  50.709 ms 50.545 
ms  50.533 ms
  8  ae-6-6.ebr2.LosAngeles1.Level3.net (4.69.148.201)  50.560 ms 50.566 
ms  50.543 ms
  9  ae-3-3.ebr3.Dallas1.Level3.net (4.69.132.78)  50.524 ms  50.418 ms  
50.407 ms
10  ae-93-93.csw4.Dallas1.Level3.net (4.69.151.169)  50.373 ms 50.310 ms 
ae-63-63.csw1.Dallas1.Level3.net (4.69.151.133)  56.827 ms
11  ae-4-90.edge3.Dallas1.Level3.net (4.69.145.200)  50.268 ms 
ae-1-60.edge3.Dallas1.Level3.net (4.69.145.8)  50.282 ms 
ae-2-70.edge3.Dallas1.Level3.net (4.69.145.72)  50.335 ms
12  LAYERED-TEC.edge3.Dallas1.Level3.net (4.71.170.6)  50.386 ms 52.124 
ms  51.458 ms
13  www.centos.org (72.232.194.162)  51.202 ms !X  51.118 ms !X 51.113 ms !X


which is only 8 hops to that same LosAngeles1 gateway.

anyways, I never have any problems seeing it, so my guess is, your 
problem is in the first 15 hops you didn't show.

btw, the traceroute worked from my host using both -I and -T (icmp and 
tcp respectively) traces.




-- 
john r pierce                                      37N 122W
somewhere on the middle of the left coast

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