41 lines
2.4 KiB
Markdown
41 lines
2.4 KiB
Markdown
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# Domain name system
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## Introduction Domain Name System
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[Source: DNS security presentation](http://www.slideshare.net/srikrupa5/dns-security-presentation-issa)
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A Domain Name System (DNS) translates a domain name such as [www.example.com](http://www.example.com/) to an IP address.
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DNS is hierarchical, with a few authoritative servers at the top level. Your router or ISP provides information about which DNS server(s) to contact when doing a lookup. Lower level DNS servers cache mappings, which could become stale due to DNS propagation delays. DNS results can also be cached by your browser or OS for a certain period of time, determined by the [time to live (TTL) ](https://en.wikipedia.org/wiki/Time_to_live) .
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- NS record (name server) - Specifies the DNS servers for your domain/subdomain.
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- MX record (mail exchange) - Specifies the mail servers for accepting messages.
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- A record (address) - Points a name to an IP address.
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- CNAME (canonical) - Points a name to another name or `CNAME` (example.com to [www.example.com](http://www.example.com/)) or to an `A`record.
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Services such as [CloudFlare](https://www.cloudflare.com/dns/) and [Route 53](https://aws.amazon.com/route53/) provide managed DNS services. Some DNS services can route traffic through various methods:
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- [Weighted round robin](http://g33kinfo.com/info/archives/2657)
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- Prevent traffic from going to servers under maintenance
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- Balance between varying cluster sizes
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- A/B testing
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- Latency-based
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- Geolocation-based
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## Disadvantage(s) : DNS
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- Accessing a DNS server introduces a slight delay, although mitigated by caching described above.
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- DNS server management could be complex, although they are generally managed by [governments, ISPs, and large companies](http://superuser.com/questions/472695/who-controls-the-dns-servers/472729) .
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- DNS services have recently come under DDoS attack, preventing users from accessing websites such as Twitter without knowing Twitter's IP address(es) .
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## Source(s) and further reading
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- [DNS architecture](https://technet.microsoft.com/en-us/library/dd197427(v=ws.10) .aspx)
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- [Wikipedia](https://en.wikipedia.org/wiki/Domain_Name_System)
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- [DNS articles](https://support.dnsimple.com/categories/dns/) |