Comodo Secure DNS

Theory and Practice for IT Professionals

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Hi everyone, Please i need help with configuration of outlook out of domain. Limited Companies and Limited Liability Partnership Companies, as per law have to display their company registration number on the following:. This could result in loss of the domain name registration and failure of the transfer. This procedure is off cource NOT a best practice. The top of the hierarchy is served by the root name servers , the servers to query when looking up resolving a TLD.

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Domain Name System

For IPv4, the domain is in-addr. For IPv6, the reverse lookup domain is ip6. The IP address is represented as a name in reverse-ordered octet representation for IPv4, and reverse-ordered nibble representation for IPv6. When performing a reverse lookup, the DNS client converts the address into these formats before querying the name for a PTR record following the delegation chain as for any DNS query.

For example, assuming the IPv4 address ARIN's servers delegate Users generally do not communicate directly with a DNS resolver. Instead DNS resolution takes place transparently in applications such as web browsers , e-mail clients , and other Internet applications.

When an application makes a request that requires a domain name lookup, such programs send a resolution request to the DNS resolver in the local operating system, which in turn handles the communications required. The DNS resolver will almost invariably have a cache see above containing recent lookups.

If the cache can provide the answer to the request, the resolver will return the value in the cache to the program that made the request. If the cache does not contain the answer, the resolver will send the request to one or more designated DNS servers. In the case of most home users, the Internet service provider to which the machine connects will usually supply this DNS server: In any event, the name server thus queried will follow the process outlined above , until it either successfully finds a result or does not.

It then returns its results to the DNS resolver; assuming it has found a result, the resolver duly caches that result for future use, and hands the result back to the software which initiated the request. Some large ISPs have configured their DNS servers to violate rules, such as by disobeying TTLs, or by indicating that a domain name does not exist just because one of its name servers does not respond. Some applications, such as web browsers, maintain an internal DNS cache to avoid repeated lookups via the network.

This practice can add extra difficulty when debugging DNS issues, as it obscures the history of such data. These caches typically use very short caching times — in the order of one minute. Internet Explorer represents a notable exception: Google Chrome triggers a specific error message for DNS issues. Hostnames and IP addresses are not required to match in a one-to-one relationship. Multiple hostnames may correspond to a single IP address, which is useful in virtual hosting , in which many web sites are served from a single host.

Alternatively, a single hostname may resolve to many IP addresses to facilitate fault tolerance and load distribution to multiple server instances across an enterprise or the global Internet. DNS serves other purposes in addition to translating names to IP addresses. For instance, mail transfer agents use DNS to find the best mail server to deliver e-mail: An MX record provides a mapping between a domain and a mail exchanger; this can provide an additional layer of fault tolerance and load distribution.

A common method is to place the IP address of the subject host into the sub-domain of a higher level domain name, and to resolve that name to a record that indicates a positive or a negative indication. E-mail servers can query blacklist. Many of such blacklists, either subscription-based or free of cost, are available for use by email administrators and anti-spam software.

To provide resilience in the event of computer or network failure, multiple DNS servers are usually provided for coverage of each domain.

At the top level of global DNS, thirteen groups of root name servers exist, with additional "copies" of them distributed worldwide via anycast addressing.

Each message consists of a header and four sections: A header field flags controls the content of these four sections. The header section contains the following fields: The identification field can be used to match responses with queries. The flag field consists of several sub-fields.

The first is a single bit which indicates if the message is a query 0 or a reply 1. The second sub-field consists of four bits indicating the type of query, or the type of query this message is a response to. A single-bit sub-field indicates if the DNS server is authoritative for the queried hostname.

Another single-bit sub-field indicates if the client wants to send a recursive query "RD". Another sub-field indicates if the message was truncated for some reason "TC" , and a four-bit sub-field is used for error codes. The domain name is broken into discrete labels which are concatenated; each label is prefixed by the length of that label.

The answer section has the resource records of the queried name. A domain name may occur in multiple records if it has multiple IP addresses associated. TCP is also used for tasks such as zone transfers. Some resolver implementations use TCP for all queries. The Domain Name System specifies a set of various types of resource records RRs , which are the basic information elements of the domain name system.

Each record has a type name and number , an expiration time time to live , a class, and type-specific data. Resource records of the same type are described as a resource record set RRset. The order of resource records in a set, which is returned by a resolver to an application, is undefined, but often servers implement round-robin ordering to achieve load balancing. When sent over an Internet Protocol network, all records use the common format specified in RFC NAME is the fully qualified domain name of the node in the tree [ clarification needed ].

On the wire, the name may be shortened using label compression where ends of domain names mentioned earlier in the packet can be substituted for the end of the current domain name.

A free standing is used to denote the current origin. TYPE is the record type. It indicates the format of the data and it gives a hint of its intended use. For example, the A record is used to translate from a domain name to an IPv4 address , the NS record lists which name servers can answer lookups on a DNS zone , and the MX record specifies the mail server used to handle mail for a domain specified in an e-mail address.

For example, in the following configuration, the DNS zone x. The A record for a. As this has the result of excluding this domain name and its subdomains from the wildcard matches, an additional MX record for the subdomain a.

The role of wildcard records was refined in RFC , because the original definition in RFC was incomplete and resulted in misinterpretations by implementers. The original DNS protocol had limited provisions for extension with new features. This was accomplished through the OPT pseudo-resource record that only exists in wire transmissions of the protocol, but not in any zone files.

The feature is described in RFC This facility is useful to register network clients into the DNS when they boot or become otherwise available on the network. Originally, security concerns were not major design considerations for DNS software or any software for deployment on the early Internet, as the network was not open for participation by the general public. However, the expansion of the Internet into the commercial sector in the s changed the requirements for security measures to protect data integrity and user authentication.

Several vulnerability issues were discovered and exploited by malicious users. One such issue is DNS cache poisoning , in which data is distributed to caching resolvers under the pretense of being an authoritative origin server, thereby polluting the data store with potentially false information and long expiration times time-to-live.

Subsequently, legitimate application requests may be redirected to network hosts operated with malicious intent. Other extensions, such as TSIG , add support for cryptographic authentication between trusted peers and are commonly used to authorize zone transfer or dynamic update operations. Some domain names may be used to achieve spoofing effects.

In many fonts the letter l and the numeral 1 look very similar or even identical. This problem is acute in systems that support internationalized domain names , as many character codes in ISO may appear identical on typical computer screens. This vulnerability is occasionally exploited in phishing. Considerable attention has been given to the adverse privacy implications. Even if DNS records cannot easily be read, modified or spoofed due to security extensions, a person with access to the DNS server or the traffic stream "on the wire" may have little difficulty in matching the IP address of the device which often identifies the user , to the websites, email or other domains they visit, and track how often and when these records are queried, since DNS records typically expire and must be requeried regularly.

DNS can also "leak" from otherwise secure or private connections, if attention is not paid to their configuration, and at times DNS has been used to bypass firewalls by malicious persons, and exfiltrate data, since it is often seen as innocuous. The right to use a domain name is delegated by domain name registrars which are accredited by the Internet Corporation for Assigned Names and Numbers ICANN or other organizations such as OpenNIC , that are charged with overseeing the name and number systems of the Internet.

A registry is responsible for operating the database of names within its authoritative zone, although the term is most often used for TLDs.

A registrant is a person or organization who asked for domain registration. As of , usage of RDAP is being considered. Registrant information associated with domain names is maintained in an online database accessible with the WHOIS service. From about , most Generic top-level domain gTLD registries have adopted this so-called thick registry approach, i.

The domain registry e. Some domain name registries, often called network information centers NIC , also function as registrars to end-users, in addition to providing access to the WHOIS datasets. The registrants users of a domain name are customers of the registrar, in some cases through additional subcontracting of resellers. These RFCs have an official status of Unknown , but due to their age are not clearly labeled as such.

From Wikipedia, the free encyclopedia. For other uses, see DNS disambiguation. This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources.

Unsourced material may be challenged and removed. September Learn how and when to remove this template message. This article or section may be written in a style that is too abstract to be readily understandable by general audiences.

Please improve it by defining technical terminology, and by adding examples. Internet portal Computer Science portal. Retrieved November 19, Domain Names - Implementation and Specification. Retrieved 18 December Paul Mockapetris - Internet Hall of Fame". Summer Conference, Salt Lake City Retrieved 28 July Domain Names - Domain Concepts and Facilities. Retrieved 17 December Retrieved 20 October Kurose and Keith W.

A Top-Down Approach, 6th ed. Eastlake 3rd November , p. Domain Name Use and Trends in 1H Archived from the original on 22 December Retrieved from " https: Computer-related introductions in Domain name system Application layer protocols Internet Standards.

OWA is not as professional as Outlook Anywhere. However this only got me half way there….. This happened because GoDaddy no longer allows you to include the non-real domains like. Users outside the firewall would use external DNS servers and be pointed to the external addresses. Once that was done, I had to use the Exchange Management shell to point the below internal URLs to the external urls which were in the new Cert.

What probably kept the SRV record from working for you alone was an autodiscover. I installed a new SSL SAN cert on their only Exchange server SP3 yesterday, and today users are receiving certificate name mismatch prompts when opening their Outlook clients. The previous cert had the local host name in the SAN cert, but given the changes around using local host names in certs soon to be implemented, I Ieft these entries out this time around with the new cert.

I already have a split horizon DNS zone within the local domain, which contains an A record for Autodiscover. Split horizon DNS zone: One thing I have noticed with Autodiscover is that internally it can end up looking at the AD before it starts looking at the actual domain of the email addresses you put into Outlook.

You may need to make sure that when you run the Outlook profile wizard that you completely erase what gets auto-populated and never accept what it puts in by default there, since that may be referencing the local AD and Exchange DN for the mailbox you are trying to add internally.

This is a normal part of the Autodiscover lookup since it looks at domain. AD actually holds some information for configuring Exchange so Outlook will pick that info up and attempt to use it for configuration. Also, sorry I took so long to response. So everything I have tried to get the autodiscover to work in the outside world fails — users on first setup get the ceritificate error issue and then occasionally get it on future logons.

It will look at domain. We have an A record that points autodiscover. Would love to send you any info that would help diagnose the issue if you are offering in an email offline. Are you using a hosted exchange provider? That info will help a lot in figuring out your issues. But I should point out that the SRV record is the last thing exchange will look for and if it sees the autodiscover. If you use a SRV, you have to remove autodiscover. The mail server is hosted internally — Exchange Should the autodiscover record be A or C?

We have an A right now. Out of curiosity, if you were to navigate in a web-browser to https: If so, what host names are on the certificate that shows up when you do that?

Well internally I did not have a record for it — so I added it to point to the server. It asked for credentials — So I gave them.

Then it presented Invalid Request. From what I understand we have a UC Cert. Can you email me some more information on your environment? Like the domain name and whatnot? My email address should be in the About page on here. I had a similar circumstance. To fix it, I had to set up a split DNS i. Cannot open the Outlook windows. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed. I have re-done the SRV record 3 times with the same result.

My autodiscovery address is correct and i tested it and it works using mydomain. Exchange Autodiscover Episode 2: Hey checked the SCP and it points to correct autodiscover…. There are some registry entries that control Autodiscover caching. Do a google search on autodiscover cache for outlook. That should give you something. We are struggling to solve the mismatched name and certificate security alert using and external hosted Exchange provider and an SBS server that has never had its copy of Exchange running.

The certificate that is referenced by the security alert was issued to sbs. Following the instructions above, we deleted the autodiscover CNAME record that existed in the internal dns zone i. Regardless of whether we set the SRV record to point to the external hosted Exchange server, to autodiscover.

We have also tried adding an SRV record to the external dns zone i. We have also deleted the autodiscover CNAME record at our domain registrar that pointed to the hosted Exchange server and substituted an SRV record pointing to that server. The security alert still occurs. Outlook autodiscover tests successfully in Microsoft Remote Connectivity Analyzer with the autodiscover CNAME record at our registrar pointed to the hosted Exchange server the connection is successful using the http redirect method.

I wrote another blog post on that. If you go find the entry outlined in that blog post, you should be able to either change the SCP so it points to the external server, or delete the SCP altogether. By the way, I solved the SRV connection issue, which was occuring because hosted Exchange provider uses a different IP address to listen for autodiscover connections on port than it does for autodiscover connections on port I changed the SRV record to point to the address that listens on part and autodiscover is working.

This left me with the original certificate error. I followed the instructions in the blog post you referenced and changed the SCP from the default internal location to the hosted Exchange provider and the certificate sercurity alert is gone. Thanks, a very useful article. We have a number of Exchange installs out there, that, while most are using an external SRV record for autodiscovery, they all have. Creating a new SRV record and adding the entries as seen in screenshots will do what you need.

Domain Joined machines are usually the ones that will have this problem, though, because they are on the. Changing the settings for the Autodiscover SCP will resolve the issue for those computers.

If you want to spend the extra money on a SAN or Wildcard cert, you can just use a regular A record for autodiscover. I will re-read the article and have a play around and see how I get on. Thanks a lot for the help. Autodiscover was being skewed. I migrated from sbs to exchange and the dns autodiscovery fix helped me fix the outlook autodiscovery mismatch.

Well done and simple. I am sorry to say that none of the solutions mentioned above have helped in my situation. I have spent the past week with little food, little sleep, and much aggravation.

I not only had to rebuild my Exchange infrastructure from scratch twice, but also almost lost my entire AD. I have just about had it.

I cannot make any internal Outlook client connect with an internal Exchange autodiscover service — or any other service — NEVER. No matter what I try and I have tried all of the solutions mentioned about, read all white papers, reviewed all documentation, etc. The errors range from unable to connect to the exchange server, to a complete inability to authenticate with the Exchange server. Both Outlook and Exchange have the latest patches 6 for exchange, and the latest SP for Office.

And if anyone has a simple 3-step answer, or a simple instruction sheet on how to make this work, I would be grateful. It uses MAPI, which is a completely different protocol.

And its functions are anything but simple. When the environment is set up according to best practices, Autodiscover is extremely easy to configure. Go there and click on the client tab, then download the Connectivity Analyzer tool. Install it, run it, and see what it comes back with. Finally, I would also like to note here that this solution, and the Part 2 solution I wrote a few months ago, are only meant to address Certificate error messages that pop up when adding a new profile or opening outlook.

In the situation where you get certificate errors, you will still be able to connect with Outlook. In terms of paying for a consultant, you are preaching to the choir. I know as I am sure you do from your statement that hiring a consultant saves time and resource, which translates into dollars saved in the end.

There is no point in wasting time. Today I am very lucky for your suggestion. I took some time, got some sleep, and stepped back from the problem for 10 hours. Once I identified the problem food and sleep did help in this case , it was resolved in about 30 seconds.

Again I thank you for you suggestions, for all the help you have provided me, and the help you provide to others. In a world that has turned into a completely cut-throat, hateful IT environment, it is good to see people who are still willing to help. Thanks for posting this, i have added the srv record however is till get certificate warning error? The dns record is correct as you have instructed.

Check the second post I wrote on the subject. For systems on the domain, the certificate error is usually due to the settings for the Autodiscover SCP in Active Directory. The link to the second post is at the top of this one. Please help me out! All mails in the MS Outlook on all system can neither send nor receive email. What do I do. This is urgent please. I feel I need to do something on the DNS to make it work bcos. Local domain is exactly the same with the website.

As for certificates, do i need a SAN in this case? The domain joined computers you have are using the Autodiscover SCP to get their configuration information the second article I wrote on autodiscover covers that. The DNS setting you use depends on what you need to accomplish. If you have a single-name cert, you have to use a SRV record for autodiscover if the name on the cert is not autodiscover.

If you have no Internal zone for domain. You can check that with the instructions in the latest article on here. This is part of the reason for new recommendations on domain naming in AD. You can use an Internal CA or self-signed certificate and not get errors as long as that certificate is deployed to the Trusted Third Party Root CAs certificate store on any client computer that accesses the Exchange server.

Certificate deployment can be a huge pain in the rump. SRV record with no autodiscover. The gotchas you deal with have more to do with usernames vs. Some of that gets a little too complicated to cover easily in writing, but I can help you out over the phone or with a remote session when you start dealing with that if you are interested.

Just shoot me an email at the address in the About section here. The GUID it shows you is the actual mailbox location for that user. So that GUID will be different for each user account. As to Certificates, as long as you use SRV records, a single name cert will work fine for you.

You can test by installing the certificate into the trusted root CA store on a client computer with the cert you have now, though. For this you would actually need to remove the Exchange Autodiscover service connection point or change it to point to autodiscover.

I wrote a follow up post on how to do this. What is best practice here? If I use mail. This means that internal clients will use Public IP addresses to communicate with Exchange. If I would like autodiscover to use domain2. Have created a DNS Zone locally named autodiscover. Can you clarify a little?

Are you wanting to use domain2. I understand a little better now. The powershell command you wrote above will set things up to allow domain joined clients to use domain2. For this to work the way you want with the connectivity analyzer, you would need to set up a SRV record on your external DNS for domain1.

Hi, I have create an srv record but after that I cannot open outlook with this error message: I tried the same and removed the internal zones I created for public zones and it has not worked.

Though it does work if I create the public zone in internal DNS with certificate error. In test lab I have applied internal CA certificate and the certificate server acts as both root and issuing certificate. The other entry covers the Autodiscover SCP, which is part of where your error is coming from. SRV records are good for making sure extra email domains can use Autodiscover and for getting autodiscover to work with a certificate that has only one host name entry.

Configuring it in the internal domain will allow you to redirect non-domain joined computers as well, however, domain joined computers work differently. The instructions should be similar for Server Thank you and sure, We will go for upgrade but this is long procedure but for time begging could you please anyone give us the best solution for windows server as how can we set up an internal DNS record for the external mail FQDN in windows by steps.

It is possible to deploy a registry modification that will suppress that message. Info is somewhere in the comments here. Sorry for the delay…Have you resolved this? If not, could you clarify a little? Are the users getting certificate errors in Outlook, or something else? If they are getting certificate errors, which of the three issues in the Certificate Error box have a red X next to it? Thank you for this. Our certificate is for mail. I set up a new SRV with xxx.

Check all of the URL settings for your virtual directories. Just getting to Autodiscover is only part of the process. You also need to make sure that Autodiscover is sending the correct URLs. Almost all of our URLs are https: This can usually be fixed by running a Repair on the account in the profile.

Another option could be Outlook Provider misconfiguration. If you had a Wildcard certificate before, someone may have changed this to match the wildcard certificate, and it would likely need to be changed back to mail.

This is great information, thank you for posting this. Could adding a SRV record for autodiscover. Anything that could help point me in the right direction would be very much appreciated.

I wrote another article about that. Having to rekey and reimport the ssl certificate was one of my worries, so much so that I got as many external devices in just to make sure that the internet ones were all good!!!

The name on the security certificate is invalid or does not match the name of the target certificate servername. In my internal primary dns companyname. If I understood correctly I must remove that record and instead create a SRV where domain is company. Go check that one out, since it more than likely applies to your situation.

That setting, by default, is servername. Hello, it is me again, finally today I was able to test the certificate issue. What I did was. The I followed your instructions.. But what you need to do is in my other article.

Run this in powershell:. Comment should still be here. Hello, for some reason I can not reply to you in the post above. After that I removed the srv record and put back the original A record for discover, restart web services but still same result…I really thought that changing the internaluri would work…. EWS, in particular, needs to match the certificate as well.

If you have more questions or would like me to take a look at things for you, you can email me at adam acbrown-it. Hello, sorry to bother you but I was wondering if you had any more suggestions I can follow, all my intranet users using outlook client still getting the same proxys certifixate error.

Hello Adam, it is me again, I just want to say a super hyper mega THANKS for your help, you keep helping me during all this time and thanks to your kind suggestions and skills I was able to sort out this problem. I have to say that nowadays is very difficult to find people keen on do what you do, so kudos to you!!!!! Lately, some users can not connect to outlook due to error 10 — outlook is unable to connect to proxy server.

This particular error is caused by the internal url value for outlook anywhere being set incorrectly. The autodiscover certificate is started after Mail server upgradations from smarterMail 15 to 16x. This can happen if the linux server is hosting a website at http: If you have the other issue, with a linux server hosting http: That DNS record should be pointing to the Exchange server.

This would need to be done internally and externally. Right now, if I go to autodiscover. It has its own way of handling Autodiscover. You will need to remove any DNS entries for autodiscover.

This can be suppressed with the following configuration changes in the registry: The pop ids are not prompting the login password in outlook 10 in exchange server but the users having mail alias ids under the main id sterling asking the password in very 5 minutes. You are commenting using your WordPress. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Main menu Skip to content.

The Issue By now, anyone who has managed, deployed, or worked with an Exchange or later environment should be familiar with Autodiscover. The Cause To solve the issue with certificates, you need to configure your environment so it enforces the appropriate action with Autodiscover. It will take the following pattern when checking for Autodiscover services: Click on it, and make sure there are no A records for autodiscover. Enter the settings as shown below: Hit OK to finish adding the record.

Other Nifty Stuff There are some additional benefits to utilizing the Service Locator record for Autodiscover rather than an Autodiscover A record, even in your public domain. Can this message be hidden, or automatic trust by some GPO or something? This does not seem to be an issue in other versions of Outlook. I would appreciate your help guys. Hi thanks for your reply, The certificate that outlook detects is incorrect it detects a public certificate that from my knowledge has never been purchased.

Will it solve this problem as well? Does that make sense? Sorry by CAS do you mean client access server or certificate authority server? Hi, I need some help, please. Hi, Thanks for replying so fast. Why would this happen and how can I fix this without buying a new certificate? Server1 — Domain Controller Server2 — Exchange Server Exchange server setup fresh but clients internally cannot connect to the server using Outlook.

So far I can confirm the following: I created a self signed cert with loads of entries including: Would you be so kind to help me out? Hi Sir, We do have a forward lookup zone autodiscover.

Furthermore at this moment I do not have a valid certificate for the second server. Please help as this may cause me my job because i am not skilled with Exchange. Since i cannot paste the output of the Autodiscover test using Miscrosoft Remote Connectivity Test, please click here to download: Users outside the firewall would use external DNS servers and be pointed to the external addresses Once that was done, I had to use the Exchange Management shell to point the below internal URLs to the external urls which were in the new Cert.

Managing Domain Name Servers