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
[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 msInteresting. 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
[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