Purpose

SIP services sometimes suffer from degradation caused by slow DNS response. 

PortaSwitch uses DNS for: 
  1) Resolving IP addresses for NTP time servers;
  2) Resolving IP addresses for CNAM lookup;
  3) SIP forwards using domain names;
  4) For ORACLE SCAN.

 
To improve this behavior internal caching should be introduced into each affected component usage of already implemented. So configuring DNS caching service should improve latency and stability.

Specifications

References

  1. http://oss.segetech.com/intra/srv/dnsmasq.conf
  2. http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html

Definitions, acronyms and abbreviation

DNS - The Domain Name System is a hierarchical decentralized naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities.

Dnsmasq - is a Domain Name System forwarder and Dynamic Host Configuration Protocol (DHCP) server for small computer networks, created as free software.

NTP - The Network Time Protocol is a networking protocol for clock synchronizationbetween computer systems over packet-switched, variable-latency data networks. 

CNAM - is an acronym which stands for Caller ID Name.


 

 

 

Ticket NumberYT:PC-251
Target Buildmr58-0
AreaConfigurator

 

 

 Business Requirements

  • N/A

Implementation

Testing 

  • N/A

1 Comment

  1. Oleg Shevtsov

    In my memory, there are several situations with DNS that require our attention:

    1. Customer-provided DNSes do not respond at all (unavailable: crashed, moved, blocked by FW etc).
    2. Delays / slow response, often of random behavior.
    3. Customer does not have own DNS servers or own DNS servers are managed by stubborn IT dept etc. It creates difficulties with setting up database for Oracle: SCAN, VIP etc.


    This solution covers only 2) for the requests that are in cache. For the requests that are not in cache - oops. In ticket TT#504509#txn-25691831, cache miss rate is ~60-70%.
    For 1) - the cache will expire. If DNS server is not available longer than the expiration of cache - we have the same issue, but delayed by ~10 minutes.

    As for 3) - we can configure it in both: normal DNS server and DNS cache. I like a normal DNS server, because additionally to caches, it resolves the names and works even when customer's DNS is slow.