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SME Server:Documentation:Administration Manual:Appendix (view source)
Revision as of 09:25, 8 October 2007
, 09:25, 8 October 2007Rewrite to include DNS basics
Allowing a third party, such as a systems integrator or networking company, to install your ethernet can be a good idea. It can help you select, procure and install the appropriate ethernet adapters, hub and cables. There are also various how-to guides available in bookstores if you are committed to installing it on your own.
Allowing a third party, such as a systems integrator or networking company, to install your ethernet can be a good idea. It can help you select, procure and install the appropriate ethernet adapters, hub and cables. There are also various how-to guides available in bookstores if you are committed to installing it on your own.
====Appendix B. Dynamic DNS Services====
<!--
The original title of this article was 'Appendix B. Dynamic DNS Services'
The following pages link to that address:
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Chapter3
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Chapter5
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Booklet
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Chapter3/de
http://wiki.contribs.org/SME_Server:Documentation:Administration_Manual:Appendix/de
-->====Appendix B. DNS====
DNS or the Domain Name Service is a distributed system of servers designed to translate human-readable names into computer routable IP addresses.
=====DNS Basics=====
SME, by design, does not respond to DNS queries from outside your local network, and ''cannot'' be used as a public DNS server for anyone outside your location.
If you want your SME server to be available to users outside your office using a ''name'' instead of your IP address, you MUST:
* Register your domain name with a Registrar
* Configure your host names on a publicly accessible DNS Server
Note: you can avoid 'Registering' your domain name if you use [[#Dynamic DNS Services]]
Imagine the following scenario:
Root_DNS
| Registrar
| / DNS Server
| / / Other_DNS
| | / /
Internet---Other_ISP---Remote_User
|
Your_ISP---Your_ISPs_DNS
|
SME
|
Local_User
Let's assume that
* SME has IP Address a.b.c.d
* SME has domain name mysmeserver.com
* Remote_User is configured to use Other_DNS for DNS lookups
If Remote_User tries to browse to http://mysmeserver.com, his computer asks Other_DNS how to find 'mysmeserver.com'. Other_DNS server then
* asks the Root_DNS servers for the Registrar in charge of 'mysmeserver.com'
* asks the Registrar for the DNS_Server that will answer queries about 'mysmeserver.com'
* asks the DNS_Server for the IP address of 'mysmeserver.com'
* saves the answer in its local cache for the amount of time specified by the administrator of the DNS record at DNS_Server.
If, on the other hand, Remote_User asks for information about your IP address (a.b.c.d), his DNS server
* asks the Root_DNS servers where d.c.b.a.in-addr.arpa is registered.
* asks the Registrar where to get more info about d.c.b.a.in-addr.arpa. This is probably but not necessarily Your_ISPs_DNS.
* asks the host indicated by the Registrar (probably Your_ISPs_DNS) what name belongs to 'd.c.b.a.in-addr.arpa'. The return value is almost always a generic filler based on your IP address unless you contact your ISP and ask them to change the PTR data for your IP address.
Basically, PTR records are managed by the organization that controls the IP address (which makes sense, if you think about it).
If Local_User tries to open http://mysmeserver.com (assuming a default SME installation with DHCP and therefore DNS provided by the SME server):
* If mysmeserver.com is configured for Local resolution, the SME server returns the data that has been configured locally.
* If mysmeserver.com is configured to use Internet DNS Servers, the SME proceeds just as the first example from Root_DNS to Registrar to DNS_Server to local cache (actually, it checks the local cache first...)
So, for you to host a public web server at your own location you need:
* An ISP to provide connectivity
* A DNS Registrar where you can 'register' your domain name and publish the addresses of your DNS servers.
* A DNS service provider who will respond to queries about your domain
Some ISP's provide registration and DNS hosting capabilities as part of the connectivity package.
Some ISP's provide DNS hosting but not Registration as part of the connectivity package.
Some Registrars provide DNS hosting as part of the registration.
Sometimes you will need 3 separate vendors for these separate services.
If you have already registered your domain name, find out if your Registrar provides DNS hosting services, and if so, how to configure them. They'll provide you with a web address where you can configure your DNS.
If they do NOT provide DNS hosting services, your ISP might. Ask them. If so, configure your DNS on their servers, then edit the Registrar page to point to the DNS servers indicated by your ISP.
If neither your Registrar nor your ISP provides DNS hosting, you'll need to find a 3rd party vendor to do this. See [[#DNS_Service_Providers]] below.
If you have not yet registered your domain name, try to find a Registrar who provides free DNS services.
=====PTR Records=====
PTR Records (or Pointer records, or Reverse DNS records) are used by internet hosts to convert an IP address into a name - sometimes for information only, sometimes for identity verification.
PTR records are constructed by ''reversing'' your IP address and appending the special suffix 'in-addr.arpa'. For example, the PTR record for ''a.b.c.d'' is ''d.c.b.a.in-addr.arpa''.
A DNS lookup for a PTR record looks just like a DNS lookup for a domain name at this point - Root_DNS, Registrar, DNS_Server, except that the return value will be a host name instead of an IP address.
With very few exceptions all PTR records are registered to the ISP that controls the IP block in question, so frequently the ONLY way to change your PTR records is to contact your ISP and request that they be changed.
PTR records are only rarely used for their original purpose of verifying the identity of a particular computer - this is now done with SSL certificates and Trust Authorities.
The PTR record for your SME Server only becomes important if you plan to deliver email directly from your SME to recipient email servers (without using your ISP's mail server as a relay). Some email providers will not accept your email if the name returned by the 'reverse lookup' of your IP address does not in its turn result in your IP address when it, itself is looked up. It doesn't necessarily need to match your configured domain name, but it has to work both ways.
For example, if the ''nslookup d.c.b.a.in-addr.arpa'' (the reverse lookup for your IP) returns ''dsl-a-b-c-d.mycity.myispsname.com'' then before trying to send email directly from your SME to the Internet at large you want to make sure that ''nslookup dsl-a-b-c-d.mycity.myispsname.com'' returns your ''a.b.c.d'' and not an error or some other address.
=====Dynamic DNS Services=====
If your IP address is assigned dynamically, you may find it helpful to use a dynamic DNS service. A dynamic DNS service provides you with an automated way to notify them whenever your IP address changes so that they can immediately publish new DNS records for your domain. Without dynamic DNS, you would have to contact your ISP to have them change your DNS records, and your web site and other services would be unavailable for several days until the change was processed. You can easily enable the usage of a dynamic DNS service by selecting it on your server console.
If your IP address is assigned dynamically, you may find it helpful to use a dynamic DNS service. A dynamic DNS service provides you with an automated way to notify them whenever your IP address changes so that they can immediately publish new DNS records for your domain. Without dynamic DNS, you would have to contact your ISP to have them change your DNS records, and your web site and other services would be unavailable for several days until the change was processed. You can easily enable the usage of a dynamic DNS service by selecting it on your server console.
{{Note box|Dynamic DNS services are not perfect. They merely point hostnames to IP addresses. If your system receives an IP address via DHCP or PPPoE, it will automatically update the dynamic DNS service each time it comes online. However, when your server disconnects from the Internet, with most dynamic DNS services your server does not indicate that it is offline in any way to the dynamic DNS service. If your system is offline for a period of time, it is possible that someone else will be assigned your IP address by your ISP. If this occurs, with most dynamic DNS services this other system will now start receiving your e-mail and web page requests until your server comes back online and updates the service with your new IP address. There is not much you can do about this, but you should be aware of this fact if there is any chance your system will be offline for a long period of time.}}
{{Note box|Dynamic DNS services are not perfect. They merely point hostnames to IP addresses. If your system receives an IP address via DHCP or PPPoE, it will automatically update the dynamic DNS service each time it comes online. However, when your server disconnects from the Internet, with most dynamic DNS services your server does not indicate that it is offline in any way to the dynamic DNS service. If your system is offline for a period of time, it is possible that someone else will be assigned your IP address by your ISP. If this occurs, with most dynamic DNS services this other system will now start receiving your e-mail and web page requests until your server comes back online and updates the service with your new IP address. There is not much you can do about this, but you should be aware of this fact if there is any chance your system will be offline for a long period of time.}}
=====DNS Service Providers=====
Here is a brief list of vendors who provide DNS service hosting. The inclusion of a vendor here does not constitute endorsement by the SME developers.
* Zoneedit http://www.zoneedit.com $free
* DynDNS http://www.dyndns.org $24.95USD per year (for 'Custom DNS' services)
* EasyDNS http://www.easydns.com $19.95USD per year
====Appendix C. Proxy Servers====
====Appendix C. Proxy Servers====