a guest Oct 15th, 2019 79 Never
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- # DNS Records
- ### `A record`
- - is used to create a mapping between an **address** and **IP**. Here, A stands for Address. You can map more than one addresses to same IP by creating multiple A records. Also, you can map an address to more than one IPs for redundancy by creating multiple A records.
- ### `CNAME record`
- - is used to create a mapping between one address and another address. It is not used to map an address with IP. Here, CNAME stands for Canonical Name. This record is used when you need to alias one address with different other names.
- - Do not use this record if you need to retain the original name for some other purpose such as MX record (email).
- - Do not use this for root domain address.
- ### `ALIAS record`
- - is used to create alias names for an address, or if you want to alias root domain. It works fine even if you have other records for the same orignal name.
- ### `URL record`
- - is used to redirect (301 redirect) instead of resolving an address to a destination.
- # `dig` tool
- DNS lookups and debugging can be done using a tool named `dig` - domain information groper.
- ### `dig +trace`
- eg: `dig +trace google.com`
- This trace results shows the way how an address is resolved.
- To resolve an address,
- - it first asks any of available root servers to find out gtld (top level domain) name servers.
- - from one of gtld, it finds out name servers
- - from one of name server, the A record is obtained
- - from A record, the IP address is obtained and reaches that server
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