My network has had a fixed public address for a long time, and I've enjoyed the benefits of OpenDNS. However, lately - during the last week or two - there have been problems with loading facebook; it just times out. If I change the router setup to use my ISP's DNS servers the page loads in an instant. So facebook does not appear to be blocked (no indication of that) - it just doesn't load when I use OpenDNS, and this started happening just some days ago (there have been days in between when it heen ok, but the last 2-3 days, no luck). I've even removed all filtering from my OpenDNS settings (and flushed caches, etc.), just in case.

Anything else I could try?

Here are the results, the DNSs definitely point to different addresses:

>nslookup www.facebook.com.
Server: bbsrv5.loqal.no
Address: 82.194.192.38

Non-authoritative answer:
Name: www.facebook.com
Addresses: 2a03:2880:2110:3f01:face:b00c::
69.63.190.70


>nslookup www.facebook.com. 208.67.222.222
Server: resolver1.opendns.com
Address: 208.67.222.222

Non-authoritative answer:
Name: www.facebook.com
Addresses: 2a03:2880:2110:3f01:face:b00c::
69.171.247.21


>nslookup static.ak.fbcdn.net.
Server: bbsrv5.loqal.no
Address: 82.194.192.38

Non-authoritative answer:
Name: a749.dsw4.akamai.net
Addresses: 2001:6c8:160::c3d7:2519
2001:6c8:160::c3d7:252f
195.215.221.91
195.215.221.73
Aliases: static.ak.fbcdn.net
static.ak.facebook.com.edgesuite.net


>nslookup static.ak.fbcdn.net. 208.67.222.222
Server: resolver1.opendns.com
Address: 208.67.222.222

Non-authoritative answer:
Name: a749.dsw4.akamai.net
Addresses: 2001:680:12:500::3e29:1268
2001:680:12:500::3e29:126a
77.67.27.26
77.67.27.56
Aliases: static.ak.fbcdn.net
static.ak.facebook.com.edgesuite.net


>nslookup -type=txt debug.opendns.com. 208.67.222.222
Server: resolver1.opendns.com
Address: 208.67.222.222

Non-authoritative answer:
debug.opendns.com text =

"server 7.fra"
debug.opendns.com text =

"flags 20 0 2fe 0"
debug.opendns.com text =

"id 7976929"
debug.opendns.com text =

"source <my public ip>:57365"

Thanks, rotblitz! I've now opened a ticket. For what it is worth, here are the results from the last two tests:

Tracing route to a195-215-221-91.deploy.akamaitechnologies.com [195.215.221.91]
over a maximum of 30 hops:

1 * * * Request timed out.
2 9 ms 9 ms 7 ms 188.113.65.49
3 16 ms 9 ms 9 ms 82.194.192.5
4 12 ms 18 ms 19 ms 82.194.192.1
5 27 ms 8 ms 8 ms 213.236.164.249
6 24 ms 24 ms 25 ms ae-1.alb2nqp7.dk.ip.tdc.net [83.88.21.83]
7 26 ms 25 ms 24 ms a195-215-221-91.deploy.akamaitechnologies.com [195.215.221.91]


Trace complete.

Tracing route to 77.67.27.26 over a maximum of 30 hops

1 * * * Request timed out.
2 397 ms 10 ms 7 ms 188.113.65.49
3 11 ms 9 ms 19 ms 82.194.192.5
4 16 ms 15 ms 15 ms te3-5.ccr01.osl01.atlas.cogentco.com [149.6.116.57]
5 31 ms 31 ms 31 ms te0-1-0-5.ccr21.ham01.atlas.cogentco.com [130.117.2.177]
6 42 ms 41 ms 41 ms te0-4-0-3.mpd21.fra03.atlas.cogentco.com [154.54.63.29]
7 39 ms 40 ms 41 ms xe-4-3-0.fra23.ip4.tinet.net [77.67.74.41]
8 40 ms 41 ms 40 ms 77.67.27.26

Trace complete.

The staff hasn't come up with a likely cause or solution yet. However; more or less by chance I started pinging facebook.com with various buffer sizes when connected to OpenDNS (in router). That's when I noticed that I got a reply for sizes below 1472 bytes. My router has a default MTU of 1500. So I reduced the MTU in the router setup to 1472, and now I can open the facebook web site.

So what I don't understand is: why would the use of OpenDNS affect this? Does OpenDNS route my request through nodes that don't allow buffer sizes above 1472 bytes, while my ISP's DNS servers avoid such problems??