NCS Texas Engineering - CS Department

NCS Texas Engineering - CS Department

Paper Presentation CAP 6135 Outline Review - DNS Proposed Solution Simulation Results / Evaluation Discussion Page 2 Domain Name System - DNS

DNS is a name resolution service which resolves host names into IP address DNS is a distributed database application with a hierarchical structure DNS Benefits Convenience: names are easier to remember Consistency: IP address can change but server names can remain constant Simplicity: One naming convention

Page 3 Domain Name System - DNS Key Components of DNS DNS name space Name servers DNS Zones Resource Records Page 4

DNS Namespace Page 5 Step 1: Your PC sends a resolution request to its configured DNS Server, typically at your ISP. Your PC ISP Recursive DNS server

Tell me the Address of www.google.com Page 6 Step 2: Your ISPs recursive name server starts by asking one of the root servers predefined in its hints file. Tell me the Address of www.google.com ISP Recursive DNS server

Root Servers I dont know the address but I know whos authoritative for the com domain ask them Page 7 Step 3: Your ISPs recursive name server then asks one of the com name servers as directed. Tell me the Address of

www.google.com ISP Recursive DNS server com DNS servers I dont know the address but I know whos authoritative for the google.com domain ask them Page 8 Step 4: Your ISPs recursive name server

then asks one of the google.com name servers as directed. Tell me the Address of www.google.com ISP Recursive DNS server google.com DNS server The Address of www.google.com is 216.239.53.99

Page 9 Step 5: ISP DNS server then send the answer back to your PC. The DNS server will remember the answer for a period of time. Your PC ISP Recursive DNS server The Address of www.google.com is 216.239.53.99 Page 10

Step 6: Your PC can then make the actual HTTP request to the web server. Send me the www.google.com.au web page Your PC www.google.com web server Here it is!

Page 11 Summary WEB (HTTP) Request root DNS servers google.com.au Web Server 6 1

3 5 Your PC ISP Recursive DNS server The actual web request com DNS servers DNS requests

DNS google.com DNS server Page 12 Caching Huge volume of request DNS resolution process allows for caching for a given period of time after a successful answer Determined by a value called the time to live (TTL) TTL is set by the administrator of the DNS server

Page 13 Summary Caching WEB (HTTP) Request root DNS servers google.com.au Web Server

6 1 3 5 Your PC ISP Recursive DNS server The actual web request com DNS servers

DNS requests DNS google.com DNS server Page 14 Proposed Solution DNS resolvers cache responses to improve lookup performance and reduce lookup overhead A resolver can use cached responses upto the time-to-live

(TTL) value associated with the response Modify resolvers - do not expunge cached records with TTL value expired Expired records evicted from cache and stored stale cache Resolvers use stale cache to answer queries for unavailable zone Allows the resolution process to continue Page 15 Proposed Solution

Page 16 Proposed Solution Page 17 Evaluation DNS traffic Cornell Computer Science Dept Internet

~1300 hosts 65 days 84,580,513 DNS queries 53,848,115 DNS responses 4,478,731 unique names Stale cache size: 1 to 30 days Attack duration: 3, 6, 12 and 24 hours. Page 18

Fraction of Queries Answered Page 19 Fraction of Accurate Records in responses Page 20 Fraction of Queries (for two-level names) Answered and Accurate Records Page 21

Fraction of Queries (for three-level names) Answered and Accurate Records Page 22 Stale cache memory footprint Page 23 Discussion

Pros DNS Robustness Simplicity. Does not change the basic protocol operation and infrastructure Does not impose any load on DNS Does not impact the latency of query resolution

Incremental Deployment Motivation for Deployment Page 24 Discussion Objections DNS caching semantics and the possibility of inaccurate information being used Autonomy for zone operators

Attackers attempting to force the use of inaccurate information Resolution latency in the face of an attack Page 25 References Mitigating DNS DoS Attacks, Hitesh Ballani, Paul Francis, CCS 2008 Wikipedia Amplified DNS DDoS Attacks and Mitigation, www.cert-in.org.in

www.cs.rpi.edu/~hollingd/netprog/notes/dns www.aptld.org Page 26

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