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An open journal-- some of it written for you, but most of it is for me.

Intro to DNS

With Maarten Balliauw

  • people know should more about DNS and the http level

DNS 101

  • How the internet works

    • IPv4 or IPv6
    • Check own operating system files to see if the host file has a record is known
    • will check the DNS cache for the local machine
    • OS will ask the router and check its own host file and DNS cache
    • same process for the ISP
    • the ISP will then go to the root server, address of the authoritative server
    • 6 hubs look ups

    • nslookup google.com

    • dig A google.com +trace

    • two types of servers

      • authorative (owns the domain)
      • cache (recursor) -> resolves the domain for you
    • DNS protcol designed in 1983
      • designed to map a domain name to an IP address
      • added TXT records and IPv6
    • TLD managed by separate organizatons (verisign, canadian internet registrartion authority)
      • all make their own rules e.g. need to be a canadian to be a .ca domain name, transfer rules
    • hierarchical system:
      • hit . first
      • then TLD like org, com, ca
      • can also create maps within a specific domain and could create own hierarchy like google does
    • caches
      • TTL -
      • cannot clear cache at ISP
      • keep the old IP address to maintain both
  • DNS zones

    • UDP protocol
    • only 13 root servers across the world
    • root-servers.org
    • $100k/yr to get own TLD
    • ? where does the money for those fees go for buying a TLD?

    • a text file and are hierarchical

    • SOA -> start of authority
    • Name of authoritive master name server (NA)

    • CNAME - redirect at the DNS record

    • MX - find mail server at specific address
    • TXT - validate domain ownership/spam rules
    • SRV - descibes a service type and port (like for in network printer)
    • PTR - reverse DNS

    • zone transfers

      • most IPs require more than 1 nameserver
      • master name server and that will sync with slave nameservers
      • no authentication and may expose internal services

Security

  • old protocol
  • cache poisoning
  • DNSSEC - checks the origin - certificate chain
  • most modern browsers are checking for DNSSEC records

  • DDoS

    • lots of open resolvers out there
    • DNS amplication for DDos
    • disable recursion

DNS in application archtecture

  • DNS failover and load balancing
  • add multiple DNS records -> will be a poor man’s load balancer because it will return an random record
  • intelligence DNS server (CNS)
  • configuration in DNS
    • use DNS as a configuration store
    • DNS record could point to a TXT value
  • service discovery

DNS for fun and profit

  • Abusing DNS

    • public hotspots
    • proxy server translating HTTP
  • iodine - same HTTP over DNS - tunnel traffic

    • code.kryo.se/iodine

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