Networking & dns 101

Marc Cluet – Lynx Consultants

What we’ll cover?

¡  Understand how networking works ¡  Understand all the basic networking protocols ¡  Understand how DNS works ¡  Be more awesome!

Lynx Consultants © 2013

What is a Network?

¡  A computer network, or simply a network, is a collection of computers and other hardware interconnected by communication channels that allow sharing of resources and information.[1] Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. A network is a group of devices connected to each other. Networks may be classified into a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, benefit, and organizational scope. (gotta love Wikipedia)


So in plain words…

¡  A network connects 2 or more computers together §  LAN (Local Area Network) is inside a known location (office,

home, etc) §  WAN (Wide Area Network) is a

network that connects two or more LANs


The Internet

¡  Internet is a network that connects in a fault tolerant way many networks

¡  Our current version of the Internet works over the protocol IPv4 with the new protocol IPv6 starting to have some presence


Internet IPv4

¡  The most common protocol in Internet is right now IPv4 ¡  IPv4 has been the Internet protocol since 1980 (RFC 760) ¡  IPv4 uses 32 bit addresses, having a total space of

4,294,967,296 unique IPs


IPv4 IP address

¡  An IPv4 IP address is divided in 8 bit chunks (1 byte per number)


IPv4 IP netmask

¡  A netmask defines what your local network is, anything inside that netmask is considered local to you


IPv4 Problems

¡  IPv4 is running out of IP addresses (last /8 delivered this year) ¡  IPv4 is not secure for most uses ¡  IPv4 was designed in the 70ies so its up for a review


IPv6 saves the day!

¡  IPv6 is the new internet protocol ¡  Uses 128 bit addresses ¡  There’s more IP addresses in IPv6 than atoms on planet

Earth


IP gateways

¡  As IP is the Internet Protocol it has to know how to talk to other networks

¡  A gateway server is the one who sits in two networks at the same time, relying packets between those networks


So then how the Internet works?

¡  Gateways keep relying your message from network to network until it reaches the destination

¡  The path to reach its destination can change all the time


IP protocols

¡  IP can run lots of different protocols inside, the most known ones are §  TCP (Transmission Control

Protocol) §  UDP (User Datagram Protocol) §  ICMP (Internet Control Message

Protocol)


IP protocol definitions

¡  TCP sends packets with complete assurance that they’ll reach their destination

¡  UDP sends packets without any kind of assurance that they’ll reach their destination

¡  ICMP sends control messages auxiliary to the IP protocol (like ping, traceroute, etc)


TCP Protocol

¡  Keeps track of all the packets it sends (serial num)

¡  Destination acknowledges (ACK) every packet received

¡  Packets can arrive in any order and they’ll be reordered at destination


TCP Ports

¡  TCP can listen or talk in several “channels” at the same time ¡  Ports are the channels where TCP (and UDP) talk, there’s a

total of 65,536 channels ¡  Most common Ports

§  80 http §  443 https §  25 smtp §  110 pop3 §  143 imap


UDP Protocol

¡  UDP sends packets as TCP to ports, but there’s no guarantee that the packets will reach its destination.

¡  This is ideal for any kind of protocol that doesn’t need all its packets §  Video Streaming §  Radio Streaming


ICMP Protocol

¡  ICMP sends auxiliary messages that help Internet routing ¡  Used in all of our common diagnostic tools

§  PING (icmp echo) §  TRACEROUTE (icmp route)


ICMP - Ping

¡  Ping sends a packet to a destination and reads the reply ¡  Bases itself on ICMP echo ¡  Can be filtered by routers and inbetween policy filters


ICMP - Traceroute

¡  Traceroute sends requests to every single hop between us and a destination

¡  This is based on one special type of ICMP packet ¡  Some routers can decide to filter traceroute, in that case *

will appear instead of the TTL


What is DNS?

¡  The Internet works with IP addresses ¡  How can we remember always that google is 173.194.67.103? ¡  It’s humanly impossible!


DNS saves the day

¡  DNS is a service (listens on UDP port 53) ¡  DNS will give you the IP address of any name you want ¡  It can give you more than one address for extra redundancy


DNS Servers

¡  DNS is also a security risk, you don’t want everyone to know your full DNS structure

¡  Big companies will show you a different DNS “view” based on where you are


DNS Geo Balanced

¡  DNS is also very useful to be able to send you to the nearest point

¡  Try resolving www.google.com from different parts of the world!


www.google.com is 173.194.41.84

www.google.com is 74.125.26.104

Questions?


Technology

Networking & dns 101