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

Rock

RockSockDoc at gmail.com
Thu Feb 28 17:12:34 UTC 2013


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?





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