Telematics. 14th Tutorial - Proxies, Firewalls, P2P

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1 Telematics 14th Tutorial - Proxies, Firewalls, P2P Bastian Blywis Department of Mathematics and Computer Science Institute of Computer Science 10. February, 2011 Institute of Computer Science Telematics Tutorial 10. February,

2 Outline 1. SSH Tunneling 2. Traffic Shaping 3. Firewalls 4. Secure Network Topology 5. Peer-To-Peer Networking 6. Movie Time 7. Up and Down Institute of Computer Science Telematics Tutorial 10. February,

3 SSH Tunneling As you probably know, SSH can be used to create (secure) tunnels. Follow the steps to access the Telematics assignments over an SSH tunnel. 1. You need a console SSH client or some alternative, e.g., PuTTY: uk/~sgtatham/putty/download.html 2. Setup the SSH tunnel with some random local port and port 80 as endpoints between your host and some faculty computer, e.g., xian: ssh -L LOCAL PORT:cst.mi.fu-berlin.de:80 Institute of Computer Science Telematics Tutorial 10. February,

4 SSH Tunneling 3. Add the following mapping in the hosts file in you operating system: cst.mi.fu-berlin.de 4. Open the following URL in a web browser: PORT 5. Download one of the Telematics assignments 6. Use Wireshark or any alternative tool to capture the data traffic between the two hosts Explain why step 3 is required and what happens when it is omitted.??? Institute of Computer Science Telematics Tutorial 10. February,

5 SSH Tunneling The server is a virtual host Host field in HTTP header is evaluated If the host entry is omitted, you are accessing the website without the tunnel (and the randomly selected TCP port should be closed) The host entry resolves cst.mi.fu-berlin.de to localhost and thus the tunnel is used as well as the right value inserted into the host field Institute of Computer Science Telematics Tutorial 10. February,

6 Traffic Shaping Explain the token and leaky bucket schemes and how they are applied in computer networks.??? Institute of Computer Science Telematics Tutorial 10. February,

7 Traffic Shaping Token an leaky bucket are two algorithms two limit the data sent into the network Token bucket 1 token added to bucket at rate r Bucket has maximum size b 1 packet may pass when a token is available (consumes token) Throughput is limited by token rate but bursts are possible In time t, (r t + b) packets may pass Leaky Bucket Packets are added to bucket 1 packet per time unit leaks out of bucket, i.e., may pass If maximum size of bucket is reached, packets are dropped Enforces rigid output pattern at average rate Bursts are not possible Alternative: count bytes instead of packets Applied in routers together with other traffic shaping approaches Institute of Computer Science Telematics Tutorial 10. February,

8 Firewalls What are firewalls and on which layer(-s) of the ISO/OSI reference model do they operate???? Institute of Computer Science Telematics Tutorial 10. February,

9 Firewalls Filtering service Implemented in software and/or hardware Protects particular subnetwork Filtering based on any header and payload data Most often found as IP packet filters Many services: User control Access control Behavior control Direction control, load balancing Logging Hiding of internal network specifics Institute of Computer Science Telematics Tutorial 10. February,

10 Firewalls In 1 Routing 3 5 Out Routing 2 4 Upper stack layers Figure: Linux Netfilter Hooks Institute of Computer Science Telematics Tutorial 10. February,

11 Firewalls by Jan Engelhardt, last updated based in part on Josh Triplett's graph Netfilter packet flow; hook/table ordering INPUT PATH Protocol/Application Layer xfrm (e.g. ipsec) decode socket lookup FORWARD PATH local routing process decision OUTPUT PATH xfrm encode raw output conntrack Network Layer mangle output reroute check filter nat xtables (ip, ip6) input output ebtables mangle input nat table only consulted for NEW connections filter output raw mangle nat prerouting conntrack prerouting prerouting routing decision mangle forward filter forward mangle postrouting nat postrouting Link Layer filter input mangle forward filter forward mangle postrouting nat postrouting nat output filter output nat postrouting ingress bridge check broute brouting nat prerouting raw prerouting conntrack mangle prerouting nat prerouting bridging decision filter forward mangle forward filter forward nat postrouting mangle postrouting nat postrouting egress interface output Figure: Linux Netfilter Packet Flow Institute of Computer Science Telematics Tutorial 10. February,

12 Firewalls Figure: Linux Netfilter Packet Flow - Input Path Institute of Computer Science Telematics Tutorial 10. February,

13 Firewalls Figure: Linux Netfilter Packet Flow - Forward Path Institute of Computer Science Telematics Tutorial 10. February,

14 Firewalls Figure: Linux Netfilter Packet Flow - Output Path Institute of Computer Science Telematics Tutorial 10. February,

15 Secure Network Topology Connect a LAN to the Internet /29 for your servers (max. 2 3 servers) /16 for internal/private network (max hosts)??? Institute of Computer Science Telematics Tutorial 10. February,

16 Secure Network Topology Service LAN world-wide WWW server SMTP server SMTP and POP3 server DNS server 1 DNS server 2 DHCP server Printer with network connection Management server with administration tools Multiple workstations Institute of Computer Science Telematics Tutorial 10. February,

17 Secure Network Topology 1. Create network topology, assign IP addresses to hosts 2. Define rule sets for both firewalls as follows??? Institute of Computer Science Telematics Tutorial 10. February,

18 Secure Network Topology Institute of Computer Science Telematics Tutorial 10. February,

19 Secure Network Topology inetnum: netname: ACHSES descr: Rechen- und Kommunikationszentrum der RWTH Aachen descr: Wendling Weg 10; Aachen; Germany country: DE admin-c: GS199 tech-c: GS199 status: ASSIGNED PI mnt-by: DFN-LIR-MNT mnt-lower: DFN-LIR-MNT mnt-routes: DFN-MNT mnt-irt: IRT-DFN-CERT source: RIPE # Filtered Institute of Computer Science Telematics Tutorial 10. February,

20 Stateless Firewall: Secure Network Topology Nr Protocol Src. IP Src. Port Dest. IP Dest. Port Action 1 TCP * * (WWW) ALLOW 2 TCP (WWW) * * ALLOW 3 TCP * * (SMTP) ALLOW 4 TCP (SMTP) * * ALLOW 5 UDP * * (DNS) ALLOW 6 UDP (DNS) * * ALLOW 7 TCP * * 80 (WWW) ALLOW 8 TCP * 80 (WWW) * ALLOW 9 TCP * * * * DENY Rule 1 and 2 allow hosts in the Internet to get access to the WWW server Rule 3 and 4 allow hosts in the Internet to get access to the SMTP server Rule 5 and 6 allow DNS requests from the Internet Rule 7 and 8 allow WWW connections from the local network. Because of the NAT module integrated into the other firewall, packets from the local network have the IP address Rule 9 discards all other packets. Institute of Computer Science Telematics Tutorial 10. February,

21 Stateful Firewall Secure Network Topology Nr Protocol Src IP Src Port Dest IP Dest Port State Action 1 TCP /16 * * 80 SYN ALLOW 2 TCP * /16 * ESTAB ALLOW 3 TCP * /29 22 SYN ALLOW 4 TCP / * ESTAB ALLOW 5 TCP * SYN ALLOW 6 TCP * ESTAB ALLOW 7 TCP * SYN ALLOW 8 TCP * ESTAB ALLOW 9 UDP * ALLOW 10 UDP * ALLOW 11 * * * * * - DENY Rule 1 and 2 allow WWW connections initialized from the local network Rule 3 and 4 allow the administrator to establish SSH connections into the subnet /29 Rule 5 and 6 allow SMTP connections between both SMTP servers, which are initialized by the internal SMTP server Rule 7 and 8 allow SMTP connections between both SMTP servers, which were initialized by the SMTP server in the DMZ Rule 9 and 10 allow DNS traffic between both DNS servers Rule 11 discards all other packets. Institute of Computer Science Telematics Tutorial 10. February,

22 Peer-To-Peer Networking 1. Discuss the peer-to-peer (P2P) networking principle 2. Name and explain properties to classify P2P networks??? Institute of Computer Science Telematics Tutorial 10. February,

23 Peer-To-Peer Networking Different approach to networking than client-server principle Every participation node is client and server: servent Goal: no single point of failure, self organized, data distribution and storage P2P networks are overlay networks Most often application layer protocols Different addressing scheme in overlay than in network layer Paths in overlay can be suboptimal regarding network topology Metric for evalution of P2P networks: overlay stretch Institute of Computer Science Telematics Tutorial 10. February,

24 Peer-To-Peer Networking Figure: Overlay Network Example Institute of Computer Science Telematics Tutorial 10. February,

25 Peer-To-Peer Networking Classification of P2P Networks: Structure Structured: content distributed according to some algorithm Unstructured: content placed randomly in the network Topology Centralized Decentralized Overhead: communication overhead and required memory per node Institute of Computer Science Telematics Tutorial 10. February,

26 Peer-To-Peer Networking Figure: Complexity of P2P networks, source LNCS 3485 Institute of Computer Science Telematics Tutorial 10. February,

27 Movie Time Watch the movie Warriors of the Net: download Look for inaccuracies and discuss the content / representation of computer networks in the tutorial session. Institute of Computer Science Telematics Tutorial 10. February,

28 Movie Time Discuss! Institute of Computer Science Telematics Tutorial 10. February,

29 Up and Down How often is the protocol stack traversed when a host is connected to a network and the user tries to view a website in the browser???? Institute of Computer Science Telematics Tutorial 10. February,

30 Up and Down There is no definite answer because it depends on the configuration. Let s consider the following: The hostname of the webserver is not statically configured DHCP is used for auto-configuration Ethernet is used on layer 1 and 2 Default gateway and DHCP and DNS server are not the same host The station has not sent any packets previously... Institute of Computer Science Telematics Tutorial 10. February,

31 Up and Down 1. Auto address configuration 1.1 DHCP (Discovery)/UDP (Port 67)/IP (Broadcast)/Ethernet (Broadcast) 1.2 DHCP (Offer)/UDP/IP (Broadcast)/Ethernet (Broadcast) 1.3 DHCP (Request)/UDP (Port 67)/IP (Broadcast)/Ethernet 1.4 DHCP (Acknowledgement)/UDP/IP (Broadcast)/Ethernet (Broadcast) 2. Domain name resolution 2.1 ARP (Request)/Ethernet (Broadcast) [Resolving layer 2 address of DNS server] 2.2 ARP (Reply)/Ethernet 2.3 DNS (Query)/UDP (Port 53)/IP/Ethernet 2.4 DNS (Response)/UDP/IP/Ethernet 3. Establishing TCP connection 3.1 ARP (Request)/Ethernet (Broadcast) [Resolving layer 2 address of gateway] 3.2 ARP (Reply)/Ethernet 3.3 TCP (SYN, Port 80)/IP/Ethernet 3.4 TCP (SYN, ACK)/IP/Ethernet 3.5 TCP (ACK, Port 80)/IP/Ethernet 4. Download of website 4.1 HTTP (GET)/TCP (Port 80)/IP/Ethernet 4.2 DATA/HTTP/TCP/IP/Ethernet Note: This is a much simplified version. We are for example assuming that the DNS reply is only one UDP packet and omitting the TCP acknowledgements for the data as well as several HTTP packets. Institute of Computer Science Telematics Tutorial 10. February,

32 The Last Slide TM Thank you for your attention. Questions? Institute of Computer Science Telematics Tutorial 10. February,

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