kageryu
join:2007-10-08
Belmont, CA
2 edits | [Connectivity] No access to google.com from a certain comcas
(the rest of the subject should read "comcast IPs")
Vitals:
Belmont (near San Mateo), CA
Dlink DCM-202 modem w/ "needed for comcast" firmware update.
Apple Airport Extreme router w/ latest firmware.
Multiple MacOS X and Windows XP computers.
Good evening all,
I'm experiencing a frustrating problem accessing *.google.com (but not gmail.com!) from a specific IP block on Comcast. IE gives "attempt to load www.google.com failed", Safari gives me "server unexpectedly dropped the connection, which sometimes happens when the site is busy". This happens on all machines on my network.
When I connected my laptop to the cable modem directly, it worked fine. This made me suspect the router for a while, but then I noticed that Comcast's DHCP server was giving me a different IP address for my laptop (the laptop and modem both received something in the 24.xx range) than it was giving me when my router is connected (something in the 71.202.138.xx range for the router, and a 73.70.148.xx address for the modem). I tried manually assigning my laptop the same address that the router was using, and the problem cropped back up again -- this makes me confident it's not a problem with the router or the router, modem, or the combination thereof.
I thought I'd be sneaky and enter the 24.xx address into my router, and then switch it back to DHCP, therefore changing the address the Comcast DHCP server associated with it, but when I did that, I was able to get net traffic with the router configured for 24.xxx, but no google. I checked the modem configuration page, and it was back to the 73.70.148.xx address. 
Has anyone seen this kind of problem before, or have any ideas for a fix short of switching to a different router to try and get a different IP address or leaving everything disconnected for a week while I wait for the DHCP lease to expire? The neighbors also have comcast service, with no problems at all. Their router is getting a 67.188.0.xx address, and the same DNS servers I am, but their Motorola modem won't tell me what address it's getting though. Traceroutes on either connection are successful and fairly similar, but use different IP equivalents for www.google.com -- 74.125.19.147 and 74.125.19.104. (I wondered if it was a DNS issue, so I also tried putting both IP's into the web browser, but got the exact same results.)
The screwiest thing is that this problem only seems to pop up in the evenings. 
Thanks for any assistance! |
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kageryu
join:2007-10-08
Belmont, CA
| Supplemental: https://www.google.com as in »https://www.google.com/accounts/ServiceL···(etcetc) when first logging in to google acccount services (i.e. gmail) works perfectly fine. Go figure...  |
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telcolackey
The Truth? You can't handle the truth
join:2007-04-06
Death Valley, CA | Post a traceroute of the problem. |
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kageryu
join:2007-10-08
Belmont, CA
| I'm pretty sure that the traceroutes don't change when I can't access Google vs. when I can. Here's a morning traceroute from my line when it does work, I'll post another when it stops working again tonight for verification.
traceroute: Warning: www.google.com has multiple addresses; using 74.125.19.104
traceroute to www.l.google.com (74.125.19.104), 64 hops max, 40 byte packets
1 10.0.1.1 (10.0.1.1) 1.637 ms 1.987 ms 1.095 ms
2 * * *
3 68.87.198.21 (68.87.198.21) 8.487 ms 11.309 ms *
4 te-9-1-ur02.sanmateo.ca.sfba.comcast.net (68.87.192.18) 17.895 ms * 10.293 ms
5 te0-7-0-5-ar01.oakland.ca.sfba.comcast.net (68.86.90.150) 16.463 ms 12.923 ms 13.110 ms
6 68.86.85.77 (68.86.85.77) 16.219 ms 13.346 ms 16.039 ms
7 comcast-ip.car2.sanjose1.level3.net (4.79.43.134) 17.945 ms 17.030 ms 15.601 ms
8 te-4-4.car2.sanjose1.level3.net (4.79.43.133) 16.939 ms 17.359 ms 21.114 ms
9 google-inc.car2.sanjose1.level3.net (4.79.43.146) 17.823 ms 18.125 ms 16.379 ms
10 209.85.251.98 (209.85.251.98) 19.086 ms 23.834 ms 19.022 ms
11 74.125.19.104 (74.125.19.104) 15.955 ms 17.061 ms 15.461 ms |
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funchords
Hello
Premium,MVM
join:2001-03-11
Washington, DC
 ·Verizon Online DSL
 ·Skype
| reply to kageryu
I have seen exactly this on two different occasions, both in the evenings.
It's something that Google is doing.
My IP is 24.20.37.XXX.
www.google.com is CNAMEd to www.l.google.com -- yet when I do a lookup on both hostnames, I get different results!!!!!
When this problem was happening, however, I was attempting to connect to 72.14.253.XXX addresses. I added this to my hosts file:
64.233.167.147 www.google.com
And I was able to use Google with no problem. By the next morning, the problem was cleared and I removed the line from my hosts file.
--
Robb Topolski -= funchords.com =- Hillsboro, Oregon USA
Are you affected by Comcast's RST forging? How to test it! -or- Read my original report. |
|
kageryu
join:2007-10-08
Belmont, CA
4 edits | Of course after I posted it's behaving tonight.. after almost a week of problems.
Thanks for the 64.233.167.147 IP for google -- I'll use that next time it starts acting up.
Edit: GAH! Moments after I post that, it stops working. (Though manually connecting to 64.233.167.147 works fine) Here's the traceroute.
traceroute: Warning: www.google.com has multiple addresses; using 74.125.19.104
traceroute to www.l.google.com (74.125.19.104), 64 hops max, 40 byte packets
1 10.0.1.1 (10.0.1.1) 4.029 ms 3.801 ms 2.996 ms
2 * * *
3 ge-2-2-ur01.sanmateo.ca.sfba.comcast.net (68.87.198.21) 317.659 ms * *
4 te-9-1-ur02.sanmateo.ca.sfba.comcast.net (68.87.192.18) 104.467 ms 77.665 ms *
5 te0-7-0-5-ar01.oakland.ca.sfba.comcast.net (68.86.90.150) 172.582 ms 239.147 ms 324.084 ms
6 68.86.85.77 (68.86.85.77) 313.120 ms * 343.858 ms
7 comcast-ip.car2.sanjose1.level3.net (4.79.43.134) 332.399 ms 379.020 ms 349.017 ms
8 te-4-4.car2.sanjose1.level3.net (4.79.43.133) 354.420 ms 159.498 ms 282.233 ms
9 google-inc.car2.sanjose1.level3.net (4.79.43.146) 304.527 ms 108.784 ms 107.925 ms
10 209.85.251.98 (209.85.251.98) 95.072 ms 84.991 ms 72.881 ms
11 74.125.19.104 (74.125.19.104) 94.591 ms 265.911 ms 274.751 ms
I don't see any difference between the two.
Neighbor's traceroute (also not much difference):
traceroute: Warning: www.google.com has multiple addresses; using 74.125.19.103
traceroute to www.l.google.com (74.125.19.103), 64 hops max, 40 byte packets
1 74.125.19.103 (74.125.19.103) 1.982 ms 1.818 ms 1.901 ms
2 * * *
3 ge-2-2-ur01.sanmateo.ca.sfba.comcast.net (68.87.198.21) 11.942 ms 11.467 ms 22.054 ms
4 te-9-1-ur02.sanmateo.ca.sfba.comcast.net (68.87.192.18) 14.744 ms 11.875 ms 9.355 ms
5 te0-7-0-4-ar01.oakland.ca.sfba.comcast.net (68.86.90.146) 15.363 ms 13.288 ms 16.894 ms
6 68.86.85.77 (68.86.85.77) 18.626 ms 19.239 ms 23.376 ms
7 comcast-ip.car2.sanjose1.level3.net (4.79.43.134) 22.269 ms 23.082 ms *
8 te-4-4.car2.sanjose1.level3.net (4.79.43.133) 207.336 ms 189.872 ms 221.180 ms
9 google-inc.car2.sanjose1.level3.net (4.79.43.146) 19.683 ms 23.279 ms 19.456 ms
10 209.85.251.98 (209.85.251.98) 26.360 ms 25.058 ms 23.406 ms
11 74.125.19.103 (74.125.19.103) 20.459 ms 25.415 ms 19.980 ms
Digs: (+trace timed out on mine)
My modem:
; DiG 9.3.4 www.google.com
;; global options: printcmd
;; Got answer:
;; -HEADER- opcode: QUERY, status: NOERROR, id: 40327
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.google.com. IN A
;; ANSWER SECTION:
www.google.com. 603391 IN CNAME www.l.google.com.
www.l.google.com. 189 IN A 74.125.19.104
www.l.google.com. 189 IN A 74.125.19.147
www.l.google.com. 189 IN A 74.125.19.103
www.l.google.com. 189 IN A 74.125.19.99
;; Query time: 356 msec
;; SERVER: 10.0.1.1#53(10.0.1.1)
;; WHEN: Mon Oct 8 22:04:13 2007
;; MSG SIZE rcvd: 116
Neighbor's:
; DiG 9.3.4 www.google.com
;; global options: printcmd
;; Got answer:
;; -HEADER- opcode: QUERY, status: NOERROR, id: 32035
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.google.com. IN A
;; ANSWER SECTION:
www.google.com. 603778 IN CNAME www.l.google.com.
www.l.google.com. 261 IN A 74.125.19.104
www.l.google.com. 261 IN A 74.125.19.147
www.l.google.com. 261 IN A 74.125.19.103
www.l.google.com. 261 IN A 74.125.19.99
;; Query time: 54 msec
;; SERVER: 68.87.78.130#53(68.87.78.130)
;; WHEN: Mon Oct 8 22:04:45 2007
;; MSG SIZE rcvd: 116
Attempt to use wget on my line:
--22:11:32-- »www.google.com/
=> `index.html'
Resolving www.google.com... 74.125.19.104, 74.125.19.99, 74.125.19.103, ...
Connecting to www.google.com|74.125.19.104|:80... connected.
HTTP request sent, awaiting response... Read error (Connection reset by peer) in headers.
Retrying.
Curl:
curl: (52) Empty reply from server
Using either on the neighbor's line works fine, though wget has this different response:
Resolving www.google.com... 74.125.19.103, 74.125.19.147, 74.125.19.99, ...
Connecting to www.google.com|74.125.19.103|:80... connected.
Just for extra annoyance, trying 74.125.19.104 (which is what it tries to use on my network) works FINE on the neighbors, but trying .103 (which is what www.google.com resolves to on theirs) fails on mine.
And the stupid Airport Extreme won't let me add static routes or clone MAC addresses. (Anyone have recommendations for a nice router that will, possibly even with link aggregation / failover dual WAN's? 802.11b/g/n might be nice but I can always just use the Airport as a WAP.. their WDS implementation is kinda handy..) |
|
espaeth
Digital Plumber
Premium,MVM
join:2001-04-21
Minneapolis, MN
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1 edit | reply to funchords
said by funchords  :It's something that Google is doing. It is -- Google's DNS infrastructure is an unusually complex mix of anycast and round-robin DNS.
With anycast there are multiple a.l.google.com - g.l.google.com servers that all share the same IP address. You use the path with the shortest network hop count. (ie, ATT->GLBX hops, not traceroute hops)
For finding the closest server (latency-wise) of that group, BIND keeps track of the response times for each of the authoritative name servers for a domain. On the first query where it gets the NS server list it assigns each server an artificially low random response time. When you lookup l.google.com you get that list of authoritative servers
Once the response times are randomly assigned, the lowest response time value server is chosen to do the lookup for www.l.google.com. When it gets the response, the time gets recorded for that server. The next query will be against the server that had the 2nd lowest initial assigned time. BIND cycles through all of the servers until they all have real response times recorded, and will eventually settle in on only querying the server that responds the fastest. This likely is why you were seeing different results for each query; you were probably still hunting through the server list.
Each of the DNS servers is then setup to dole out a round-robin pool of content servers that are close to them to load balance the requests across multiple front-ends.
So:
1) Anycast gets you to the DNS servers with the fewest provider transversals.
2) Natural BIND DNS server selection will lock you in to the DNS server that's closest to you latency-wise.
3) That DNS server will dole out a round-robin pool of IP addresses that are close to it to balance your requests across the closest content engines to you.
-Eric |
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kageryu
join:2007-10-08
Belmont, CA | Thanks for the additional info.. I've forwarded all of this on to Google, hoping it will reach someone who can do something. |
|
cpgrant
join:2007-10-25
Ann Arbor, MI | kageryu, have you heard of fix for this? (aside from potentially fragile solutions of hardcoding an IP into a hosts file). I've been experiencing the same problem for a few weeks.
For what its worth, this is happening in Ann Arbor, MI. |
|
sortofageek
Premium,Mod
join:2001-08-19
Valhalla Dr
clubs:
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Host:
Team Helix
Distributed Comput..
Linksys
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| Please keep the discussion in this thread ---> »Problems loading google (DNS issues possibly?)
TIA 
--
Join Team Helix * I am praying for these friends . |
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