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Hamish's avatar
Hamish
Icon for Cirrocumulus rankCirrocumulus
Sep 23, 2008

Multiple CNAME's...

Question... Why is there a blog in F5's website recommending multiple CNAME records for a name? It pretty comprehensively violates the RFC's and in Bind v9 is also impossible to do (Since bind9 checks your syntax).

 

 

Trying to configure multiple CNAME records will likely result in an outage to your DNS servers... The docs from isc.org say the following

 

 

multiple-cnames

 

This option was used in BIND 8 to allow a domain name to have multiple CNAME records in violation of the DNS standards. BIND 9.2 onwards always strictly enforces the CNAME rules both in master files and dynamic updates.

 

 

Pretty clear really... So why do F5 push info (Admittedly in a blog) that's possibly going to cause a site outage (Or slowdown) for someone?

 

 

Sorry, but posts like this tend to push my buttons. We should be striving to keep to the standards and work with them. Not pushing violations of them that work with SOME browsewrs or SOME implementations of a service. If astandard is indeed lacking in something then perhaps we need to push for an extension that would be implemented by everyone. This just smacks of a continuance of websites that only work with a particular browser.

 

 

And that's just wrong...

 

config
design

5 Replies

  • Hamish's avatar
    Hamish
    Icon for Cirrocumulus rankCirrocumulus
    Sep 23, 2008
    yeah... There's actually two links that mention it...

     

     

    http://devcentral.f5.com/weblogs/macvittie/archive/2008/09/08/3596.aspx

     

     

    and

     

     

    http://devcentral.f5.com/weblogs/macvittie/archive/2008/09/19/3631.aspx

     

     

    The first one I have issues with because it touts the multiple CNAME records as a cool hack... The second is worse... It touts it again, along with NOT using one of the more useful features of browsers (Relative links).

     

     

    What the blogger has against persistent connections to enhance performance I don't know (They really speed things up, possibly more than many connections)... Browsers have a limit of two connections to a particular server for good reasons (Not performing a DOS on yourself being a pretty good one in my book).

     

     

  • JRahm's avatar
    JRahm
    Icon for Admin rankAdmin
    Sep 23, 2008
    Post your comments to the blog posts, she's great about active dialogs... Lively discussion benefits everyone.

     

     

  • Hamish's avatar
    Hamish
    Icon for Cirrocumulus rankCirrocumulus
    Sep 23, 2008
    I did... It was a bit shorter though, so lacks a certain something...

     

     

    Tact probably...
  • dennypayne's avatar
    dennypayne
    Icon for Employee rankEmployee
    Sep 24, 2008
    I just commented to the original blog post, I have always implemented parallelism using A records. WebAccelerator allows you to specify how many "extra" names to use for a host, so you need an A record, not a CNAME for each one (ie, if you turn the feature on for www.example.com and specify a depth of 2 you need A records for www.example.com, www1.example.com, and www2.example.com). All the A records happen to point to the same place, so I guess that effectively it's like having multiple CNAMEs.

     

     

    Denny