Test if UDP ports are open to the Internet.
Category: Internet Networking
UDP Port Scanner
article #1387, updated 44 days ago
Internet connection speed tests
article #182, updated 143 days ago
An excellent test recommended by Watchguard:
A very good one:
Here’s the first one we saw which was HTML5 only, no Flash or Java:
Here’s a commonly used one which requires Flash:
And another which uses java:
Check Your Email Blacklists
article #644, updated 189 days ago
Here’s a great place to do so:
And a third, realtime:
article #1174, updated 880 days ago
A number of Internet tools use DNSBLs (DNS blacklists) and retrieve them by HTTP/HTTPS. Here are a number of good resources for this.
Time synchronization (NTP, SNTP) setup
article #37, updated 984 days ago
In Windows Server 2012 R1/2, 2008 R1/2, 7, Vista, and 2003 SP2 and later, whenever time is out of sync, it’s good to run the following two commands in an administrative command prompt (an ordinary command prompt for 2003SP2+):
w32tm /config /manualpeerlist:pool.ntp.org,0.pool.ntp.org,1.pool.ntp.org,2.pool.ntp.org /syncfromflags:MANUAL /reliable:YES /update w32tm /resync /rediscover
/rediscover is something new to this writer, it solves problems when /resync alone does not produce correct results.
In Server 2003 SP1 and before, and XP, we use this, because /reliable doesn’t exist:
w32tm /config /manualpeerlist:pool.ntp.org,0.pool.ntp.org,1.pool.ntp.org,2.pool.ntp.org /syncfromflags:MANUAL /update w32tm /resync
Sometimes w32tm doesn’t exist as a service, and has to be registered:
Under Windows 2000, we need to go a bit more archaic:
net time /setsntp:pool.ntp.org net time /querysntp
If you are using Windows DHCP services, the above is best for the server, but for all of the workstations under its control, place the server’s IP in the Time Server option. This is probably best for a domain. When you have standalone or mobile-capable machines, best to just use the w32tm configuration above.
JEB's Diagnostic Sites
article #164, updated 1067 days ago
Here are web sites for diagnosing DNS, Internet email, and other issues.
A very good place to test Internet email servers and servers in general exposed to the Internet at large.
DNSstuff is excellent for diagnosing DNS issues of all kinds. Most of its tools require a small subscription fee.
whatismyipaddress.com is very good for obtaining geographical and ISP information for an IP address.
is very good for testing Exchange WAN services, e.g., smartphone access, Outlook Anywhere.
DNS, Whois, et cetera
article #12, updated 1071 days ago
A great place for general DNS lookup info:
The best WHOIS:
And one for info about IP addresses:
Eliminate Hesitations in Microsoft Services with Better DNS
article #1067, updated 1149 days ago
Microsoft is heavily using something called GeoIP, to optimize Internet data routing for its services, including Skype, Office 365, and all of the others.
All of the code below is within ‘nslookup’, running in CMD on Windows.
The way this works, basically, is different IP sets are reported by DNS lookups, depending on the upstream DNS server being polled. So if, like many right now, you were using Google’s DNS (18.104.22.168 and 22.214.171.124) on your LAN, and did nslookup on the recommended test hostname, outlook.office365.com, you would see this:
> outlook.office365.com Server: google-public-dns-a.google.com Address: 126.96.36.199 Non-authoritative answer: Name: outlook-namsouth2.office365.com Addresses: 2603:1036:0:26::2 2603:1036:102:90::2 2603:1036:404:a4::2 2603:1036:102:107::2 2603:1036:102:b8::2 2603:1036:404:11b::2 2603:1036:404:3f::2 2603:1036:3:12e::2 2603:1036:102:3e::2 2603:1036:404:11c::2 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 Aliases: outlook.office365.com outlook.ha.office365.com outlook.office365.com.g.office365.com >
But on the other hand, if you were using OpenDNS (22.214.171.124/222.222), you would see this:
> outlook.office365.com Server: resolver1.opendns.com Address: 126.96.36.199 Non-authoritative answer: Name: outlook-namsouth4.office365.com Addresses: 2603:1036:d01:2::2 2603:1036:101:2::2 2a01:111:f400:31ab::2 2603:1036:902:a3::2 2603:1036:906:4d::2 2603:1036:405:2::2 2603:1036:405:15::2 2603:1036:404:67::2 2603:1036:100::2 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 Aliases: outlook.office365.com outlook.ha.office365.com outlook.office365.com.g.office365.com >
The most important thing to observe in the above, is that the IP set is different. And if you try pings from your test PC to each of the above IPs, you will notice major differences. In recent testing, most of Google’s results ping much slower (higher, in milliseconds) than OpenDNS’s. But we found OpenDNS’s pings noticeably slower than our current known best of breed, Level3 (22.214.171.124/4):
> outlook.office365.com Server: resolver1.level3.net Address: 126.96.36.199 Non-authoritative answer: Name: outlook-namsouth.office365.com Addresses: 2603:1036:404:16::2 2603:1036:404:b6::2 2603:1036:102:16::2 2603:1036:405:29::2 2603:1036:906:4f::2 2603:1036:d00::2 2603:1036:102:8f::2 2603:1036:405:4a::2 2603:1036:4:4c::2 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168 22.214.171.124 126.96.36.199 188.8.131.52 184.108.40.206 220.127.116.11 Aliases: outlook.office365.com outlook.ha.office365.com outlook.office365.com.g.office365.com >
We have also noticed that the lists of IPs do not correspond to names, i.e., outlook-namsouth3 does not return the same IP list each time. So there is a lot of highly complex geographically-centered IP routing by DNS, going on, by Microsoft, and Level3 seems to cooperate best.
The upshot is, if you see any Microsoft cloud-based services being slow, hesitating, freezing up, or losing connection regularly, switch your LAN’s DNS forwarders to Level 3, and you may well knock the problem out most easily.
Great HTML5 Internet Speed Test
article #1068, updated 1149 days ago
DNS Root Servers
article #1017, updated 1332 days ago
As of this writing, the current authoritative list, from here:
|b.root-servers.net||18.104.22.168||2001:500:84::b||University of Southern California (ISI)|
|d.root-servers.net||22.214.171.124||2001:500:2d::d||University of Maryland|
|e.root-servers.net||126.96.36.199||2001:500:a8::e||NASA (Ames Research Center)|
|f.root-servers.net||188.8.131.52||2001:500:2f::f||Internet Systems Consortium, Inc.|
|g.root-servers.net||184.108.40.206||2001:500:12::d0d||US Department of Defense (NIC)|
|h.root-servers.net||220.127.116.11||2001:500:1::53||US Army (Research Lab)|