DNS Failover

1
DNS Failover

• Presenter Tim McAdoo
• Date 04/17/2007

2
Introduction

• Define Failover
• Queries
• Caching
• Registrars
• Other Protocols

3
Definition Failover

• Failover vs. Fall-over

4
DNS Query Flow
5
DNS Caching

• Caching levels
• Expiration

6
Domain Registrars

• Registrars
• WHOIS records
• Service updates

7
Example WHOIS Record

• gtwhois odu.edu
• Whois Server Version 1.3
• Domain names in the .com and .net domains can now
  be registered
• with many different competing registrars. Go to
  http//www.internic.net
• for detailed information.
• Domain Name ODU.EDU
• Registrar EDUCAUSE
• Whois Server whois.educause.net
• Referral URL http//www.educause.edu/edudomain
  
• Name Server NS1.ODU.EDU
• Name Server NS2.ODU.EDU
• Name Server NS2.WM.EDU
• Name Server NS1.WM.EDU
• Status ok
• Updated Date 06-nov-2006
• Creation Date 05-nov-1986

8
NS Failover

• Multiple NS records per domain
• WHOIS change rate

9
NS Lookup Examples

• Non-authoritative answer
• cs.odu.edu nameserver ns1.cs.odu.edu
• cs.odu.edu nameserver ns1.odu.edu
• cs.odu.edu nameserver ns2.cs.odu.edu
• ns1.cs.odu.edu internet address 128.82.4.36
• ns2.cs.odu.edu internet address 128.82.4.1
• Authoritative answer
• cs.odu.edu nameserver ns1.cs.odu.edu
• cs.odu.edu nameserver ns2.cs.odu.edu
• cs.odu.edu nameserver ns1.odu.edu
• ns1.cs.odu.edu internet address 128.82.4.36
• ns2.cs.odu.edu internet address 128.82.4.1
• ns1.odu.edu internet address 128.82.224.101

10
Other Failovers

• SMTP MX Records
• Enterprise organizations
• Keeps e-mail running

11
SMTP Diagram
Normal Operations
Failover Mode
12
Summary

• Defined Failover
• Query Process
• Caching Levels
• Registrars and WHOIS
• Other Protocols

13
Questions and Answers?