Category: DNS

Use DMARC to harden SPF and DKIM
article #1255, updated 19 days ago

The following TXT record:

v=DMARC1;p=reject;pct=100;p=reject;adkim=s;aspf=s

at least theoretically, should harden SPF and, if present, DKIM. “=s” means “strict”. According to DMARC documentation, DMARC can be used without DKIM, and experiences with a first setup of the above without DKIM are playing out well so far.

Categories:   DNS   Spam/Antispam

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The WINS resolution information was not updated. The record format is corrupt.
article #1227, updated 110 days ago

This error often occurs when a longstanding Windows Server network is given a much newer domain controller. The WINS records embedded in DNS, don’t work anymore; when you try to delete them or change them, you get the error message in the title of this article.

The best thing to do, is PowerShell:

Remove-DNSServerResourceRecord -ZoneName dns_zone.local -Force -RRtype "WINS" -Name "@"

Try that (substituting dns_zone.local for your LAN DNS zone!), then right-click on the zone name, choose “All Tasks” and then “Reload”, then press F5 for refresh. The error-causing situation will go away, you can then reconfigure easily. If there are other zones, you’ll want to repeat for all of them. If there is a WINS record in a reverse lookup zone, the RRtype is WINSR instead of WINS.

Categories:   Windows OS-Level Issues   DNS

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'dig' web interface for DNS studies
article #1137, updated 338 days ago

This is amazing:

http://digwebinterface.com

Submitted by the amazing Zach Hogan.

Categories:   DNS   

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DNS, Whois, et cetera
article #12, updated 428 days ago

A great place for general DNS lookup info:

http://www.dnsstuff.com/

The best WHOIS:

https://whois.icann.org/en

And one for info about IP addresses:

http://www.arin.net/index.shtml

Categories:   DNS   Internet Networking

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Test DMARC record for a domain
article #1086, updated 452 days ago

A free tool:

https://www.dmarcanalyzer.com/dmarc/dmarc-record-check/

Categories:   Email   DNS

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SPF for Constant Contact
article #873, updated 459 days ago

Awhile ago it came to light that the following needed to be added to SPF records for email-enabled domains using Constant Contact:

include:ccsend.com include:constantcontact.com include:confirmedcc.com

Things have gotten a lot better. The following now covers all of the above:

ip4:208.75.120.0/22

Categories:   Email   DNS

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Eliminate Hesitations in Microsoft Services with Better DNS
article #1067, updated 506 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 (8.8.8.8 and 8.8.4.4) 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:  8.8.8.8

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
          40.97.170.162
          40.97.30.130
          40.97.170.178
          40.97.142.18
          40.97.41.98
          40.97.162.130
          40.97.154.66
          40.97.166.178
          40.97.117.242
          40.97.119.178
Aliases:  outlook.office365.com
          outlook.ha.office365.com
          outlook.office365.com.g.office365.com

>

But on the other hand, if you were using OpenDNS (208.67.220.220/222.222), you would see this:

> outlook.office365.com
Server:  resolver1.opendns.com
Address:  208.67.222.222

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
          40.97.142.18
          40.97.41.98
          40.97.162.130
          40.97.154.66
          40.97.166.178
          40.97.117.242
          40.97.119.178
          40.97.170.162
          40.97.30.130
          40.97.170.178
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 (209.244.0.3/4):

> outlook.office365.com
Server:  resolver1.level3.net
Address:  209.244.0.3

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
          40.97.133.130
          40.97.132.194
          40.97.125.114
          40.97.132.226
          40.97.126.50
          40.97.31.50
          40.97.164.146
          40.97.136.194
          40.97.166.34
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.

Categories:   DNS   Internet Networking

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DNS Root Servers
article #1017, updated 689 days ago

As of this writing, the current authoritative list, from here:

https://www.iana.org/domains/root/servers

is:

a.root-servers.net 198.41.0.4 2001:503:ba3e::2:30 VeriSign, Inc.
b.root-servers.net 192.228.79.201 2001:500:84::b University of Southern California (ISI)
c.root-servers.net 192.33.4.12 2001:500:2::c Cogent Communications
d.root-servers.net 199.7.91.13 2001:500:2d::d University of Maryland
e.root-servers.net 192.203.230.10 2001:500:a8::e NASA (Ames Research Center)
f.root-servers.net 192.5.5.241 2001:500:2f::f Internet Systems Consortium, Inc.
g.root-servers.net 192.112.36.4 2001:500:12::d0d US Department of Defense (NIC)
h.root-servers.net 198.97.190.53 2001:500:1::53 US Army (Research Lab)
i.root-servers.net 192.36.148.17 2001:7fe::53 Netnod
j.root-servers.net 192.58.128.30 2001:503:c27::2:30 VeriSign, Inc.
k.root-servers.net 193.0.14.129 2001:7fd::1 RIPE NCC
l.root-servers.net 199.7.83.42 2001:500:9f::42 ICANN
m.root-servers.net 202.12.27.33 2001:dc3::35 WIDE Project

Categories:   DNS   Internet Networking

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Free Public DNS Servers
article #883, updated 749 days ago

Google is a good place to start:

8.8.8.8
8.8.4.4

OpenDNS is often good too:

208.67.220.220
208.67.222.222
208.67.220.222
208.67.222.220

And one new to us, is Level 3. Level 3 provides DNS to most ISPs in the U.S.A., and does provide geo-routing for speed and compatibility.

209.244.0.3
209.244.0.4

Categories:   DNS   

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Installing nslookup on Linux
article #1008, updated 749 days ago

Increasingly, nslookup is not installed by default in major Linux distros. On Arch-based and Debian-based distros, it’s in package dnsutils,

Categories:   DNS   Linux OS-level Issues