Routers Firewalls And Proxies - OH MY!

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A brief introduction to "How The Internet Works", from how your LAN uses MAC addresses to talk nic-to-nic, through to what a proxy is, and how that operates, plus a little bit of everything in …

A brief introduction to "How The Internet Works", from how your LAN uses MAC addresses to talk nic-to-nic, through to what a proxy is, and how that operates, plus a little bit of everything in between. Consider this the leypersons guide to the Internet.

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  • 1. Routers, Firewalls, Proxies... Oh My! An introduction to some technologies which can permit or prevent you getting to content on the Internet By Jon “The Nice Guy” Spriggs Presented for Manchester Barcamp On 7 th November 2009
  • 2. Who am I?
    • I'm JonTheNiceGuy on twitter, identi.ca, facebook, in fact, pretty much everywhere!
    • 3. I work for a major IT company as a "Network Security Specialist".
    • 4. I love Free & Open Source Software.
    • 5. Sadly, none of the products I'm about to show you are Free Software products. All of these devices (except, I think, the Switch and the Hub) can be replaced by machines running Free Software.
  • 6. How does the internet work? (Part 1)
    • All devices on an IP based network have at least two addresses, a MAC address and an IP address.
    • 7. The IP address is resolved on the LAN to a MAC address.
    • 8. If the IP address you're connecting to isn't on your LAN, the routing table tells your computer where to send the data.
    • 9. Any "first hops" (routers, firewalls, or proxies) need to be on the same LAN as your computer. Most computers will have only a Default Route.
  • 10. What is a switch or a hub?
    • A hub takes data received at one interface and pushes the same data to all the other interfaces.
    • 11. A switch looks at the MAC address or addresses associated with each interface, and sends data received at other ports only addressed to the MAC address on that interface.
    • 12. How does this compare to a Wireless Access Point?
    • 13. A Wireless Access Point acts a lot like a hub with a little added security.
  • 14. How does the internet work? (Part 2)
    • IP traffic is a bit like a telephone exchange.
    • 15. Each connection is like a phone call from one extension (or port) to another.
    • 16. The caller knows the target number and extension, the exchange knows the source extension and sends the response back to it.
    • 17. Sometimes both the source and destination extension will be hidden by the exchanges.
    • 18. Ports are also specified by protocol. The most common three are TCP, UDP and ICMP.
  • 19. What is a router?
    • A router is a device which forwards traffic from one LAN segment to another.
    • 20. It has a routing table that tells it where to send traffic to.
    • 21. It may sometimes have an access control list which can act as a basic firewall.
    • 22. It isn't very smart.
    • 23. It typically doesn't care about ports, just addresses.
  • 24. What does a router look like? From Flickr User "Star6" http://www.flickr.com/photos/stars6/2759249001/
  • 25. What does a routing table look like?
  • 26. What is a firewall?
    • A firewall is a slightly smarter router.
    • 27. It looks at the source IP address and destination IP address, as well as the destination port to decide whether it's allowed to pass it on.
    • 28. It can hide the source or destination of the traffic behind an IP address. (NAT)
    • 29. It will typically form the boundary between two or more network segments.
  • 30. What does a firewall look like? From Flickr User Air Force One - http://www.flickr.com/photos/airforceone/2472283831/
  • 31. What is a firewall?
  • 32. What is a proxy?
    • For the purposes of this talk, a proxy can be considered like a smarter firewall.
    • 33. It looks not only at route, and port, but also understands and can read some application requests and responses - usually HTTP, HTTPS, FTP.
    • 34. Proxies are typically where most policy policing occurs.
    • 35. These will usually be placed either in-line with firewalls and routers or in a separate network segment.
  • 36. What does a proxy look like?
  • 37. What is a VPN?
    • For the purposes of this talk, a VPN is an encrypted tunnel from either your machine or router to another router or firewall.
    • 38. VPNs can be configured like any other route - all traffic goes over it, or specific traffic goes over it.
    • 39. These will be secured by technologies like IPSec, SSL, or SSH.
  • 40. Is this the easiest VPN software?
  • 41. How does this lot fit together?
    • Please note that the cloud bit in the middle of this diagram is usually just a lot of routers and switches plugged into each other!
  • 42. Why am I explaining all this?
    • In my job as a Firewall engineer, lots of people blame firewalls when traffic doesn't flow properly.
    • 43. I wanted to explain that in very many situations, there's more at stake than just one or two "hops".
    • 44. This also gives you some idea about what the devices we talk about "do", and maybe understand a little more about what makes it all fit together.
  • 45. Any questions? (P.S. This doesn't mean I know the answers!) (P.P.S. I might need to take your details and get back to you later!)