This deep dive in DNS internals talk was given by Hemant and Pradeep from http://theremotelab.io Meet-up Link: http://www.meetup.com/awsugblr/events/228000779/ Blog Link: http://theremotelab.io/blog/aws-meetup-all-things-dns/

1. DNS for fun and profit
Hemant Soni
Pradeep Aradhya

2. The Remote Lab's story

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4. Agenda:
Name resolution on Linux systems
DNS server internals
Zonefiles, frequently used DNS records, TTL and DNS caches
DNS and email systems
Size and perfomance: MTU and IP fragmentation
TXT record for custom applications

5. Name resolution on Linux systems
What happens when...
Zoom into name resolution
/etc/nsswitch.conf
ltrace-n3-Sping-c1theremotelab.co.uk2>&1|less

6. DNS server internals
Who did we talk to
How did we talk
+trace
dig+tracemail.google.com
Common DNS configurations(https://help.ubuntu.com/lts/serverguide/dns-configuration.html)

7. Zonefiles, DNS records, TTL
A
PTR
CNAME
MX
TXT - the simplest and the most powerful
And many more..

8. Forward and reverse DNS lookup records
Reverse DNS usually managed by ISP

9. DNS and email systems
Let the games begin!!

10. MX records and priorities:
Why spammers use lower priorities?
Good MX records will have both forward and reverse entries

11. DKIM
How do I ensure the validity of email sender?
How do I ensure that my mail is not tampered in transit?
s . _domainkey . d
digtxt20120113._domainkey.gmail.com

12. SPF records
Am I allowed to send mail from this IP for this domain?
digtxtgmail.com
digtxt_spf.google.com
digtxt_netblocks.google.com

13. DNSBL
Reverse the IP and concatenate with the WL/BL list supporting domain
Results are hints in the context of list
We can also use this mechanism for our own custom actions

14. Size and perfomance
MTU
IP fragmentation
TCP usages

15. TXT record for custom applications
digtxtprofile.theremotelab.co.uk

16. References
DKIM(http://dkim.org/specs/rfc4871-dkimbase.html)
SPF(http://www.openspf.org/SPF_Record_Syntax)
DNSBL(https://www.spamhaus.org/faq/section/DNSBL%20Usage)

17. Questions

18. Thank you
Hemant Soni
hemant.soni@theremotelab.com(mailto:hemant.soni@theremotelab.com)
@hemant_soni_(http://twitter.com/hemant_soni_)
Pradeep Aradhya
pradeep.aradhya@theremotelab.com(mailto:pradeep.aradhya@theremotelab.com)
@aradhyapradeep(http://twitter.com/aradhyapradeep)
http://theremotelab.com(http://theremotelab.com)