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Thread: What is CNAME and MX

  1. #1
    Homestarr Mod
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    What is CNAME and MX

    can anyone explain in simple terms what exactly the CNAME and MX of a domain is?

    why would you ever want full control to alter these?

    thanks

  2. #2
    Cable Guy Jonny M's Avatar
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    Changing the MX record changes where your email goes to.

    CNAME records allow to you add subdomains, amongst other things.

  3. #3
    Don't feed the trolls... tiggerai's Avatar
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    CNAME or Canonical name, is another name for the domain, basically an Alias for the official domain.

    e.g www.google.com is actually google.akami(or something).net

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    Hexus.net Troll Dougal's Avatar
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    As tigs said.

    Also known as FQDN, http://en.wikipedia.org/wiki/Canonical_name

    Basicly the address you use could be forums.hexus.org but this could also be the same as forums.hexus.org.uk (all fake ) but forums.hexus.org. cannot be forums.hexus.org.uk

    Due to the trailing period (.)
    Quote Originally Posted by Errr...me
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    Don't feed the trolls... tiggerai's Avatar
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    Fully Qualified Domain Name.

    See... my degree taught me something useful!

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    Hexus.net Troll Dougal's Avatar
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    Quote Originally Posted by tiggerai
    Fully Qualified Domain Name.

    See... my degree taught me something useful!
    Defo well worth the few grand then
    Quote Originally Posted by Errr...me
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  7. #7
    Homestarr Mod
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    best i leave them alone then

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    MX is Mail Exchanger, it's the address of a mail server which is the designated handler for all mail sent to an @yourdomain.ext address. You'd change it if, for example your mail server isn't running on the same machine (or external IP) as your web server (quite a common config for corporates).

  9. #9
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    Wink

    For those interested, your basic dns records are as follows

    A = Address record, A records are used to map an IP address to a hostname or subdomain.

    CNAME = Canonical name, a CNAME record refereces another record, effectivley making it an alias, normaly used to map a subdomain to an existing domain.

    MX = Mail exchanger, an MX record specifies a mail server for the domain, normaly more than one will be specified and they will be given a priority to denote which server to try first (for backup mail servers etc)

    NS = Name server, an NS record lists the DNS servers responsible for the domain, again more than one can and normaly is provided so if the primary server fails a backup can be used.

    PTR = Pointer, a PTR record is used to resolve an ip address to a name, PTR records are what make reverse lookups work.

    SOA = Source of authority, a SOA record contains a lot of the basic information about the domain relating to how updates should be handled, primary name server and contact detail.

    And because im a nice guy.. you can all have a nice example zone file

    - = SOA record = -
    -------------------
    @ IN SOA ns0.example.com. hostmaster.example.com. (
    2005081701 ; Serial
    10800 ; Refresh
    3600 ; Retry
    3600000 ; Expire
    86400 ) ; Minimum

    - = MX Record2 = -
    -------------------
    MX 5 mx1.example.com.
    MX 5 mx2.example.com.

    - = NS Records = -
    ------------------
    IN NS ns0.example.com.
    IN NS ns1.example.com.

    - = A Records = -
    ----------------
    @ IN A 999.888.777.666
    cvs IN A 888.888.888.888

    These effectivley map example.com to 999.888.777.666 (yes, i know it's invalid!) and cvs.example.com to 888.888.888.888.

    It's worth noting this a record is special since the "@" means all destinations not setup in the zone file for this domain goto this, this is effectivley the "base" level of the dns.

    - = CNAME Record = -
    ----------------------
    www IN CNAME example.com.

    This maps the www subdomain (yes, it is actualy a subdomain :O) to example.com, any changes made to the record for example.com automaticly filter back to www, www.example.com will go to 999.999.999.999, subdomains can basicly be pointed anywhere you want to point them

    I've not listed a PTR record in this zone file because well, it wouldnt go in one, the PTR records would go into a zone file for the IP range as oppsed to the hostname, such a file would be named 777.888.999.in-addr.arpa and the PRT records would be specified using the last octet.

    So for example.com we'd have a PTR record like this

    666 IN PTR example.com.



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  10. #10
    Administrator Moby-Dick's Avatar
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    Miggy I'm goign to steel that post and put in a connectivity sticky if you dont mind ( with credit etc. )
    my Virtualisation Blog http://jfvi.co.uk Virtualisation Podcast http://vsoup.net

  11. #11
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    I dont mind at all
    ph33r my toothbrush, for it is made of SCROTANIUM

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