1. Firewalls and proxies Unit objectives
Discuss the purpose of a firewall
Discuss the functionality of a proxy server

2. Topic A
Topic A: Firewalls
Topic B: Proxy servers

3. An introduction to firewalls
A mechanism for controlling access between networks
Implemented within (? and sometimes outside) the router that connects the private network with the public network
Three types of firewalls:
Packet filters
Bastion hosts
Proxy servers

4. Packet filtering
The technique of examining each datagram as it passes through a router
Implemented within routers

5. Bastion hosts
A heavily fortified server on the network through which all external traffic must pass
Sits inside the firewall and is the main point of contact between the intranet and the Internet

6. Example of bastion host topology

7. Access Control Lists - ACLs
Two steps: 1. define the ACL
Example, router(config)#access-list access list number permit/deny {test conditions}
2. Apply ACL to an interface (ex. E0, s0, s1) by using the access-group command.
Router(config-if) protocol access-group access-list number in/out

8. Standard Access-list Example
Router(config)# access-list access-list-number {deny | permit} source [source-wildcard ] [log]
Access-list 33 permit log (permits all traffic from )
Access-list 44 deny log (denies traffic from host )
Access-list 55 deny any log (denies all traffic from network )
4/25/2017

9. Activity A page 12-5
Discussing firewalls

10. Firewalls and proxies
Topic A: Firewalls
Topic B: Proxy servers

11. Proxy servers Also known as IP proxy
Masks the IP address of internal hosts and represents itself instead
Types of proxy:
Winsock proxy
Web proxy
SOCKS proxy
Network Address Translation – NAT
Also Port Address Translation - PAT

12. Discussing proxy servers
Activity B page 12-7
Discussing proxy servers

13. Unit summary Discussed the purpose of firewalls
Discussed the functionality of proxy servers