M D
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DNS Aliases
When it comes to DNS aliasing my experience has always been to limit the number of aliases in use and have a single A record per host then setup aliases using CNAMEs for secondary references. I started researching as I have seen this method as well as setting up multiple A records pointing to a single host IP address. I was surprised to find that there is indeed a strong argument for both sides debating management/performance/loo kup functionality.
If you have experience with DNS and aliases I would be interested to know the EE community input on this topic.
PROS vs CONS:
Multiple A Records to Single IP Address Aliasing
A Record Definition - Domain Name to IP Address Resolution
Management - If server IP address needs to be changed all A Records need to be updated as well to the new IP address
Performance - DNS server resolves single name to get IP address
Reverse Lookup - If using multiple A Records to point to a single IP address there will only be 1 reverse lookup pointer
Multiple CNAMES to Single A Record Aliasing
CNAME Record Definition - Domain Name Alias to Primary Domain Name A Record IP Address Resolution. Canonical name records were designed to alias A records
Management - Easier to manage server IP address changes at single A Record for a multiple CNAME references
Performance - DNS server resolves 2 names before getting IP address putting more load on the resolver
Reverse Lookup - Clear understanding that this is an alias and what host it is pointed to
CNAME Chaining
Defined - Domain Name Alias -> Domain Name Alias -> Primary Domain Name A Record IP Address
Management – Multiple records to reference. Changes along the chain could break name resolution
Performance - DNS server resolves many names before getting IP address
Thanks
If you have experience with DNS and aliases I would be interested to know the EE community input on this topic.
PROS vs CONS:
Multiple A Records to Single IP Address Aliasing
A Record Definition - Domain Name to IP Address Resolution
Management - If server IP address needs to be changed all A Records need to be updated as well to the new IP address
Performance - DNS server resolves single name to get IP address
Reverse Lookup - If using multiple A Records to point to a single IP address there will only be 1 reverse lookup pointer
Multiple CNAMES to Single A Record Aliasing
CNAME Record Definition - Domain Name Alias to Primary Domain Name A Record IP Address Resolution. Canonical name records were designed to alias A records
Management - Easier to manage server IP address changes at single A Record for a multiple CNAME references
Performance - DNS server resolves 2 names before getting IP address putting more load on the resolver
Reverse Lookup - Clear understanding that this is an alias and what host it is pointed to
CNAME Chaining
Defined - Domain Name Alias -> Domain Name Alias -> Primary Domain Name A Record IP Address
Management – Multiple records to reference. Changes along the chain could break name resolution
Performance - DNS server resolves many names before getting IP address
Thanks
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Hi MD,
It would, in theory, under certain circumstances, deliver faster name resolution.
If you use a CName, and assuming that the record is not cached somewhere from your machine, through all upstream DNS servers, then the CName is resolved to the A record, and then a second query is initiated to resolve the A record to an IP address, making two queries rather than one.
I cannot imagine that is a practical issue in many cases, unless you have a very slow DNS response to start with perhaps.
I have no personal experience of having any issues with CNames, even with two 'layers' of recursion.
Alan.
It would, in theory, under certain circumstances, deliver faster name resolution.
If you use a CName, and assuming that the record is not cached somewhere from your machine, through all upstream DNS servers, then the CName is resolved to the A record, and then a second query is initiated to resolve the A record to an IP address, making two queries rather than one.
I cannot imagine that is a practical issue in many cases, unless you have a very slow DNS response to start with perhaps.
I have no personal experience of having any issues with CNames, even with two 'layers' of recursion.
Alan.
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--MD