Information Session DNS Service level recommendations and experiences
Information Session DNS Service level recommendations and experiences What is a DNS Service Level (or SLA)? SLAs are a measure of: The ability to resolve names in the name space The ability to obtain authoritative answers for domain delegations
The time taken for changes in registry data to be reflected in the name servers How to measure DNS Service Levels? These service levels are measured in a number of ways. Each has its own metric and recommended level and each deals with vastly different areas that effect DNS availability.
Service Level Measures: Overall Availability Per Name Server Availability Round Trip Time - RTT Packet Loss Average Resolution Time Scheduled Down Time DNS updates Service Level Measures - Overall Availability
This refers to the ability of an authoritative answer for DNS requests. Recommended SLA: 100% Service Level Measures Per Name Server Availability This refers to the availability of an authoritative
answer for a DNS request from each name server individually. Recommended SLA: 99.99% Service Level Measures Round Trip Time & Packet Loss This refers to the ping time and number of packets that go missing in the network that
the name server is connected to. Recommended SLA: 300ms/10% Service Level Measures Average Resolution Times This refers to the average response time for DNS queries from the time the query is received to the time the response is sent.
Recommended SLA: 250ms Service Level Measures Scheduled downtime This refers to the amount of scheduled controlled total DNS downtime allowed. Recommended SLA: No downtime
Service Level Measures DNS updates This refers to the addition, removal and modification of records in the name space, 510min updates are not uncommon, but now days they are average, with providers able to offer instant DNS updates, and propagation using IXFR. Our Recommended SLA: 20mins Max
Recommended Service Levels Summary: 100% Overall DNS Availability 99.99% Per Name Server 300ms RTT (round trip time) 10% Packet Loss maximum 250ms average resolution time No down time 20 mins Max updates How to confirm Service Levels are being met?
Normally the registry operator will perform there own SLA monitoring and report back any variations to the governing body. However you may like to measure these things yourself. Service levels such as: Overall Availability Per Name Server Availability Round Trip Time - RTT
Packet Loss Average Resolution Time DNS updates Can be measured through sampling Taking samples of each measurement over time periods is the easiest and most effective way to ensure service levels are being met. The frequency of these samples is flexible and can be decided between you and your registry
operator. Recommended sampling Frequency: Overall Availability ( 1 min ) Per Name Server Availability ( 1 min ) Round Trip Time RTT ( 1 min ) Packet Loss ( 1 min) Average Resolution Time ( 1 min) DNS updates ( 10 min )
Example: Using mrtg to sample Average Response Time `Daily' Graph (5 Minute Average) Max Response Time: 127.0 ms (0.4%)
Average Response Time: 20.0 ms (0.1%) Current Response
Time: 12.0 ms (0.0%) How to maintain good Service Levels? Choose excellent carry class data centres with redundant network connections, power etc Run multiple secondaries in diverse locations and networks
Maintain a strong and up to date understanding of DNS Use clustering at each location Use quality hardware with different OS Maintain industry best practices, such as those stated in RFC2182, 2870 etc How to co-operate with users to maintain service levels? Target larger commercial ISPs for secondary
services Making use of the existing experienced DNS companies Keep up to date, and provide discussion lists so that you can hear your communities needs. Regularly participate in discussions and show you are taking responsibility for the Name space In summary - key factors to maintaining SLAs
are: Multiple secondaries Network carrier diversity Provider diversity Monitoring Accountability Maintain industry best practice and leverage existing industry experience Thanks for listening
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