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

Topic A Topic A: Firewalls Topic B: Proxy servers

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

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

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

Example of bastion host topology

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

Standard Access-list Example Router(config)# access-list access-list-number {deny | permit} source [source-wildcard ] [log] Access-list 33 permit 172.16.0.0 0.0.255.255 log (permits all traffic from 172.16.0.0) Access-list 44 deny 172.16.13.7 0.0.0.0 log (denies traffic from host 172.16.13.7) Access-list 55 deny 172.16.64.0 any log (denies all traffic from network 172.16.64.0) 4/25/2017

Activity A-1 page 12-5 Discussing firewalls

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

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

Discussing proxy servers Activity B-1 page 12-7 Discussing proxy servers

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