1. cs490ns - cotter1 Firewalls What they do. How they work.

2. cs490ns - cotter22 Outline What is a firewall? Architectures –Stand Alone / application / proxy –Personal / host based –Gateway / packet filters –Enterprise / hardware Roles –Bastion –DMZ Packet Filtering concepts –IPTables –Stateful filtering Packet Forwarding Ethernet bridge

3. cs490ns - cotter33 What is a Firewall? A hardware or software device that monitors (and controls ?) the transmission of packets that attempt to pass through the perimeter of a network (or host). Provide 2 basic security functions –Packet Filtering –Application Proxy gateways Additional security features –Log unauthorized (and authorized ?) access attempts –Provide VPN Connections –Support user authentication –Shield internal machines from outside view

4. cs490ns - cotter44 What should a firewall do? Control the flow of packets to/from Internet Block external login as root (?) Must distinguish between local and Internet packets (even spoofed addresses) Support limited user accounts Log all system activities

5. cs490ns - cotter55 Types of Firewalls Stand Alone / application / proxy Enterprise / Local Hardware / Software Gateway / router / packet filter Personal / host based –Windows firewall – incoming protection –ZoneAlarm, Linux, etc. – incoming / outgoing filter

6. cs490ns - cotter66 Types of Firewalls Internet Corporate Network Router / packet filter Stateful Firewall Application Proxy Host-based Firewall

7. cs490ns - cotter77 Standalone Proxy Firewalls Application Gateways Intended to buffer the interface between an internal application and the Internet –Web Servers –Mail Servers –File Transfer Controls flow of packets into and out of local network –Limit access to specific web sites –Cache results for use by other internal hosts –Hide internal IP addresses from network view

8. cs490ns - cotter88 Enterprise Firewalls Intended to support larger traffic volumes Provides more sophisticated support –Stateful filtering, etc. Software –Checkpoint Firewall 1, Microsoft ISA, Semantic Enterprise, etc. Hardware –Cisco PIX, SonicWall, Watchguard, etc. Expensive!

9. cs490ns - cotter99 Gateway / Packet Filter May be embedded in sophisticated routers May be used for SOHO networks –May be incorporated into small SOHO routers –May be incorporated into a gateway host (Linux ?) Provides the ability to monitor and control packets through the gateway / router. –Generally support in / out / through filtering –May not include stateful filtering capabilities

10. cs490ns - cotter10 Host-based Firewalls Intended as a last line of defense for the host computer Runs as a background process on host –Limited bandwidth available –Generally supports incoming port filtering –Can specify which ports (if any) can support incoming connection requests. –Occasionally supports outgoing filtering (looking for worms, trojans, etc.)

11. cs490ns - cotter11 Firewall Roles Bastion Hosts –Hardened systems that typically run a firewall and perhaps an application as well DMZ – demilitarized zone –An isolated subnetwork that includes all services that are offered over the internet (and perhaps to the internal network as well).

12. cs490ns - cotter12 Bastion Firewall and Host LAN Internet Firewall Web Server

13. cs490ns - cotter13 DMZ LAN Internet WebE-mail DMZ

14. cs490ns - cotter14 What is Packet Filtering? The process of deciding which packets to allow through the filter, based on attributes of the packet –Source / Destination Port –Source / Destination IP Address –Status flags in the packet (syn) –Originating protocol (icmp, tcp, etc.) –Connection state (tcp) Linux (2.4+) supports Netfilter (based on iptables)

15. cs490ns - cotter15 How does Packet Filtering Work? Define rules to allow or block specific types of packets Firewall screens all packet headers to look for matches against the rules Apply rules in the order in which they are stored Allow or block packets based on rule matches. If a packet matches no rules, apply default behavior to the packet (usually deny).

16. cs490ns - cotter16 Packet Filtering Issues Rules are complex. Easy to introduce errors Filters based on IP addresses. If authorized sites are hacked, your site is compromised IP Spoofing can fake authorized (internal?) sites. Routers can be hacked to reroute internal packets Activities need to be logged Internal host adresses should be hidden

17. cs490ns - cotter17 Iptables Administration tool for IPv4 packet filtering and NAT Used to set up, maintain, and inspect the tables of IP packet filtering rules used by the kernel to manage packet flow through the firewall. Based on tables that specify the overall task and chains that identify the position of the packet in the packet flow.

18. cs490ns - cotter18 IPTables tables Filter table –Used to control the flow of packets based on packet attributes –Only filter packets, don’t modify packets here. Network Address Translation (NAT) table –Used to change the source / destination IP address and / or port of selected incoming / outgoing packets Mangle table –Supports specialized packet handling / routing –Change contents of packet Experimental and developing tables …

19. cs490ns - cotter19 Basic Packet Filtering Internet LAN Input Output Forward filter table RH-Firewall-1-INPUT

20. cs490ns - cotter20 Incoming Packets to Filter Illegal Incoming Source IP Addresses –Your IP Address –Your LAN Address –Private Network Addresses –Multicast IP Addresses –Loopback Interface Addresses Nuisance sites / networks Remote Source Port Filtering Local Destination Port Filtering Incoming TCP connection-state filtering Probes and Scans DoS Attacks Etc.

21. cs490ns - cotter21 Packet Filtering alert list CERT –www.cert.org – Carnegie-Mellon Software Engrg Inst.www.cert.org –www.us-cert.gov –www.us-cert.gov Port Filter List (3/08) –DNS zone transfers53 –tftpd69 –link87 –RPC / NFS111 / 2049 –BSD “r” commands512, 513, 514 –lpd515 –uucpd540 –openwindows2000 –X windows6000 +

22. cs490ns - cotter22 Outgoing Packets to Filter Why? –Consideration for fair use in Internet –Distribution of private information –Detection of unwanted client programs (Trojans, etc.) See http://www.us-cert.gov/cas/tips/ST06-001.html What –Legitimate, routable addresses only –Destination IP Addresses –Destination ports –Source Ports

23. cs490ns - cotter23 Filter TableChains May be associated with any interface (eth0, etc.) INPUT –Used to test packets that come into the firewall OUTPUT –Used to test packets that are leaving the firewall FORWARD –Used to test packets that are passing through the firewall Packets should pass through only 1 chain

24. cs490ns - cotter24 Filter table packet flow Routing Input Chain Forward Chain Output Chain Drop Local Processes Input Chain Drop

25. cs490ns - cotter25 Iptables rule structure Iptables –t “table” “action” “chain” rule “target” –Which table are we working with (filter is default) –What action do we want to do to that table (insert, delete, etc.) –Which chain in that table are we working with –What do we want to do? –Where do we go if we match the rule?

26. cs490ns - cotter26 IPTables Actions Create a new chain (-N). Delete an empty chain (-X). Change the default policy for a chain. (-P). List the rules in a chain (-L). Flush the rules out of a chain (-F). Zero the packet and byte counters on all rules in a chain (-Z).

27. cs490ns - cotter27 IPTables Actions Append a new rule to the end of a chain (-A). Insert a new rule at some position in a chain (-I). Replace a rule at some position in a chain (-R). Delete a rule at some position in a chain, or the first that matches (-D).

28. cs490ns - cotter28 IPTables targets ACCEPT –Stop processing and pass to application / OS DROP –Stop processing and block packet LOG –Packet info sent to syslog. Continue processing REJECT –Stop processing and send reject message to source DNAT –Change destination network address SNAT –Change source network address MASQUERADE –Do source network address translation (PAT)

29. cs490ns - cotter29 Example Filter Rules #Allow traffic on the loopback interface iptables –A INPUT –i lo –j ACCEPT iptables –A OUTPUT –i lo –j ACCEPT # Set Default policy for chain Iptables --policy INPUT DROP #Allow all outgoing connections iptables -A block -m state --state NEW -i ! ppp0 \ -j ACCEPT #Block incoming attempts to Xwindows iptables –A INPUT –i eth1 -p tcp --syn \ --destination-port 6000-6003 -j REJECT

30. cs490ns - cotter30 Example Filter Rules #Allow incoming connections to local web server Iptables –t filter -A block –p tcp --dport 80 --i eth1 \ -j ACCEPT #Insert a rule that allows incoming udp packets to port 12345 iptables –I block 7 –p udp –dport 12345 –j ACCEPT #Allow DNS requests NOT from outside iptables -A block –p tcp --dport 53 -m state --state NEW \ -i ! eth1 -j ACCEPT #Allow (and redirect) incoming web connections to 192.168.5.6 iptables –t nat –A PREROUTING –d eth1 -p tcp \ --dport 80 -j DNAT --to-destination 192.168.5.6

31. cs490ns - cotter31 Simple Firewall table ## Insert connection-tracking modules (not needed if built into kernel). insmod ip_conntrack insmod ip_conntrack_ftp ## Make chain that blocks new connections, except if coming from LAN. iptables -N block iptables -A block -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A block -m state --state NEW -i ! ppp0 -j ACCEPT iptables -A block -j DROP ## Jump to that chain from INPUT and FORWARD chains. iptables -A INPUT -j block iptables -A FORWARD -j block

32. cs490ns - cotter32 Iptables default config file /etc/sysconfig/iptables # Firewall configuration written by system-config-securitylevel # Manual customization of this file is not recommended. *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] :RH-Firewall-1-INPUT - [0:0] -A INPUT -j RH-Firewall-1-INPUT -A FORWARD -j RH-Firewall-1-INPUT -A RH-Firewall-1-INPUT -i lo -j ACCEPT -A RH-Firewall-1-INPUT -p icmp --icmp-type any -j ACCEPT -A RH-Firewall-1-INPUT -p 50 -j ACCEPT -A RH-Firewall-1-INPUT -p 51 -j ACCEPT -A RH-Firewall-1-INPUT -p udp --dport 5353 -d 224.0.0.251 -j ACCEPT -A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT -A RH-Firewall-1-INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT -A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited COMMIT

33. cs490ns - cotter33 CentOS 5.5 Firewall – part 1 [rcotter@lserver3 ~]$ sudo iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination RH-Firewall-1-INPUT all -- anywhere anywhere Chain FORWARD (policy ACCEPT) target prot opt source destination RH-Firewall-1-INPUT all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination

34. cs490ns - cotter34 CentOS 5.5 Firewall – part 2 Chain RH-Firewall-1-INPUT (2 references) target prot opt source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 255 ACCEPT esp -- 0.0.0.0/0 0.0.0.0/0 ACCEPT ah -- 0.0.0.0/0 0.0.0.0/0 ACCEPT udp -- 0.0.0.0/0 224.0.0.251 udp dpt:5353 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:631 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:631 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED ACCEPT tcp -- 192.168.1.0/24 0.0.0.0/0 state NEW tcp dpt:22 ACCEPT tcp -- 134.193.12.34 0.0.0.0/0 state NEW tcp dpt:22 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:137 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:138 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:139 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:445 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 state NEW udp dpt:2069 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:3128 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:3306 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited

35. cs490ns - cotter35 Filter table Input, forward chains point to custom chain –RH-Firewall-1-INPUT Output chain set to accept all –(allow any outgoing traffic) RH-Firewall-1-INPUT chain –Initial 4 rules allow broad classes of packets –Allow multicast DNS –Allow ipp (Internet Printing protocol) –Allow incoming UDP packets to port 12345 Special server set up for cs423 class –Allow incoming SSH connections –Reject everything else!

36. cs490ns - cotter36 Network Address Translation What? –“Translates” IP addresses and / or ports as packet passes through firewall –Only first packet of a connection will traverse the table. All remaining packets are modified the same as the first packet. Why? –Private local IP Addresses –Multiple Servers (load sharing) –Transparent Proxying

37. cs490ns - cotter37 NAT table Used to map local IP addresses to a set of routable addresses (NAT) Used to map local IP addresses to a set of ports associated with a single routable address (NAPT) Used to map local IP addresses to a set of ports associated with a variable routable address (masquerade) –Dial-up connection –Dynamically assigned IP address Other

38. cs490ns - cotter38 NAT Two types of NAT –Source NAT (snat) used to translate the source IP address of a packet (typically outgoing) –Destination NAT (dnat) used to translate the destination IP address of a packet (typically incoming).

39. cs490ns - cotter39 NAT table chains Pre-routing –Used to test / modify the destination addresses of incoming packets Output –Used to change the source (or destination) address of locally generated packets Post-routing –Used to change the source address of outgoing packets.

40. cs490ns - cotter40 NAT table packet flow Routing Input Chain Forward Chain Output Chain Drop Local Processes Destination NAT Pre-routing Source NAT Post-routing

41. cs490ns - cotter41 Simple NAT table rules # Masquerade out ppp0 iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE # Disallow NEW & INVALID incoming or forwarded packets from ppp0. iptables -A INPUT -i ppp0 -m state --state NEW,INVALID -j DROP iptables -A FORWARD -i ppp0 -m state --state NEW,INVALID -j DROP # Turn on IP forwarding (in RAM) echo 1 > /proc/sys/net/ipv4/ip_forward # Turn on IP forwarding (in file /etc/sysctl.conf) net.ipv4.ip_forward = 1

42. cs490ns - cotter42 Mangle table Used for special routing and packet modification. –Use TOS (type of service) field in IP header. –TTL –Can be used to set and test markers placed

43. cs490ns - cotter43 Mangle Table Routing AS Internet

44. cs490ns - cotter44 Linux Firewall Mgmt iptables –Make changes to memory image of firewall rules iptables-save –Display a copy of the memory image –Can redirect the copy to a file using output redirection –Iptables-save > /etc/sysconfig/iptables iptables-restore –Rebuild memory image from keyboard or file (using redirection) Security Level and Firewall Applet (Fedora) –Creates an automatic backup file: /etc/sysconfig/iptables

45. cs490ns - cotter45 IPTables Constraints Based on IP – only –Don’t run IPX, appletalk, etc. as these protocols are not filtered Packets traversing the filter table will pass through only 1 chain

46. cs490ns - cotter46 Port Forwarding Internet LAN 123.234.56.78:80 192.168.3.6:80 HTTPD

47. cs490ns - cotter47 SOHO Router Port Range Forwarding

48. cs490ns - cotter48 IPTables Port Forwarding For incoming packets –iptables -t nat -A PREROUTING -p tcp -d --dport -j DNAT --to-destination : For returned packets –iptables -m conntrack --ctstate DNAT -t nat -A POSTROUTING -p tcp -d --dport -j SNAT --to-source For packets originating on firewall –iptables -t nat -A OUTPUT -p tcp -d -- dport -j DNAT --to-destination :

49. cs490ns - cotter49 IPtables rerouting Issues Often, when we re-route packets, we only need to change destination (or source) IP address. Sometimes (if we are rerouting to a locally connected destination) we need to change both IP address and MAC address. IPtables only filters IP traffic. It cannot change IPX, netBEUI, Appletalk, etc.

50. cs490ns - cotter50 EBtables Ethernet Bridge tables –Intended to support filtering of packets that IPtables cannot filter – Ethernet protocol, MAC address, ARP, netBEUI, IPX, etc. –Basically adds non–IP filtering. –802.1Q VLAN filtering –MAC address NAT –Frame counters Linux bridge-nf code –Passes bridged traffic to IPtables

51. cs490ns - cotter51 EBtables Structure broute table –BROUTING chain –Choose whether to process packet at layer 2 (bridge) or at layer 3 (route) –e.g. route normal IP traffic and bridge IPX traffic filter table –FORWARD, INPUT, OUTPUT chains –Route packets based on MAC addresses nat table –PREROUTING, OUTPUT, POSTROUTING chains –Change MAC addresses (redirect based on MAC)

52. cs490ns - cotter52 Ethernet Bridge Firewall Internet LAN Linux box configured as a bridge, with firewall installed

53. cs490ns - cotter53 Ethernet Bridge Firewall Use bridging firewall (ebtables) to set up rules to pass packets through host. –Since processing happens at Data Link Layer, there is no need to assign an IP address to host interfaces, so machine is invisible to network scanning. –Offers better protection, and less configuration of the remaining network. –Can also be configured with an IDS.

54. cs490ns - cotter54 Ethernet Bridge Firewall Create a virtual Ethernet bridge interface –brctl addbr br0 Add our interfaces to the bridge –brctl addif br0 eth0 –brctl addif br0 eth1 Remove the IP configuration from interfaces –Ifconfig eth0 down –Ifconfig eth1 down –Ifconfig eth0 0.0.0.0 up –Ifconfig eth1 0.0.0.0 up Configure access for the bridge –Local console, OOB network, configure 1 IP

55. cs490ns - cotter55 Ethernet Bridge Firewall (2) Internet LAN

56. cs490ns - cotter56 Example Firewall Application Monitor all outgoing Traffic –Most firewalls only monitor incoming traffic by default Identify what traffic is desired and block the rest. –Many applications generate queries to their servers –Spyware –Hacks

57. cs490ns - cotter57 App development process Capture all outgoing traffic –Monitor traffic as it enters or leaves the network – (Ethernet Bridge) –Use iptables to log traffic. -A firewall-win1 –j LOG –log-level 4 –log-prefix “Win1” –log-tcp-options –log-ip-options –Set up syslog to divert level 4 messages to a separate file (see syslog.conf) kern.warning/var/log/iptables.log –Save data daily to separate file iptables_log_022011

58. cs490ns - cotter58 Primary Firewall Filter Table # Generated Manually 8/19/10 *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [8183:1429550] :OUTPUT ACCEPT [14722:762210] -N RH-Firewall-1-INPUT # Create separate chains for each host - 8/19/10 -N Firewall-Win2 -N Firewall-Win1 -N Firewall-lserver3 #new line 8/26/10 - start monitoring this machine -N firewall-bridge -A OUTPUT -j firewall-bridge -A INPUT -j RH-Firewall-1-INPUT -A FORWARD --src 192.168.1.25 -j Firewall-lserver3 -A FORWARD --src 192.168.1.35 -j Firewall-Win2 -A FORWARD --src 192.168.1.30 -j Firewall-Win1 -A RH-Firewall-1-INPUT -i lo -j ACCEPT -A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j ACCEPT -A RH-Firewall-1-INPUT -p esp -j ACCEPT -A RH-Firewall-1-INPUT -p ah -j ACCEPT -A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m tcp --dport 631 -j ACCEPT -A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT -A RH-Firewall-1-INPUT -j DROP

59. cs490ns - cotter59 Win1 Outgoing Firewall Chain -A Firewall-Win1 --dst 192.168.1.0/24 -j ACCEPT -A Firewall-Win1 -p icmp -m icmp --icmp-type any -j ACCEPT -A Firewall-Win1 --dst 134.193.123.45 -j ACCEPT -A Firewall-Win1 --dst 208.67.222.222 -j ACCEPT # Allow queries to Dropbox -A Firewall-Win1 --dst 50.16.0.0/16 -j ACCEPT # Allow queries to Kapersky -A Firewall-Win1 --dst 38.117.98.0/24 -j ACCEPT -A Firewall-Win1 --dst 38.124.168.0/24 -j ACCEPT -A Firewall-Win1 --dst 38.113.165.0/24 -j ACCEPT -A Firewall-Win1 --dst 79.141.216.0/24 -j ACCEPT # Allow queries to Microsoft (update) -A Firewall-Win1 --dst 207.46.206.0/24 -j ACCEPT -A Firewall-Win1 --dst 65.55.200.0/24 -j ACCEPT -A Firewall-Win1 --dst 64.4.30.0/24 -j ACCEPT -A Firewall-Win1 --dst 65.54.221.0/24 -j ACCEPT # Allow queries to dyndns.org -A Firewall-Win1 --dst 91.198.22.0/24 -j ACCEPT -A Firewall-Win1 --dst 204.13.248.0/24 -j ACCEPT -A Firewall-Win1 --dst 208.78.69.0/24 -j ACCEPT # Lots of multicast traffic. Drop it. -A Firewall-Win1 --dst 224.0.0.0/8 -j DROP # Now, log everything else before dropping it -A Firewall-Win1 -m physdev --physdev-in eth1 -j LOG --log-level 4 --log- prefix "Win1 " --log-tcp-options --log-ip-options #For everything else, reject the traffic. -A Firewall-Win1 -j DROP

60. cs490ns - cotter60 Capture Outgoing Traffic Data Record – 1 per packet –Feb 19 00:01:03 bridge kernel: Win1 IN=br0 OUT=br0 PHYSIN=eth1 PHYSOUT=eth0 SRC=192.168.1.35 DST=66.94.233.186 LEN=40 TOS=0x00 PREC=0x00 TTL=128 ID=10570 DF PROTO=TCP SPT=2323 DPT=80 WINDOW=65185 RES=0x00 ACK FIN URGP=0 –Records per day ~ 40k to 80k+

61. cs490ns - cotter61 Port Scan Attack Detector PSAD Can be configured to detect various network scans, invalid traffic, attacks, etc. Can be used to fingerprint source machines Can be configured to provide active response based on type of input, numbers of input packets for a predetermined period. Can be used to sort and organize logged data.

62. cs490ns - cotter62 Summarize traffic psad -m /var/log/iptables/iptables_log_022011 -- gnuplot --CSV-fields dst src dp:count --gnuplot- graph points --gnuplot-xrange 0:100 --gnuplot-file- prefix test_022011 –test_022011.dat –1, 172, 2 ### 1=12.29.100.148 172=192.168.1.35 –: –39, 172, 96 ### 39=66.94.233.186 172=192.168.1.35 –: –246, 171, 1 ### 246=216.191.247.139 171=192.168.1.30

63. cs490ns - cotter63 Sort Traffic by Source Use script (bash / awk / py / ?) to sort traffic into separate files by source Use DNS to get domain name for sites Win1_022011.lst –12.29.100.148: Output was 0 –: –66.94.233.186: r3.ycpi.vip.mud.yahoo.net. –: –216.137.43.236: server-216-137-43- 236.dfw3.cloudfront.net.

64. cs490ns - cotter64 Analyze traffic Are addresses identifyable? Is the traffic known / expected? Why is traffic there?

65. cs490ns - cotter65 References Firewalls and VPNs – Principles and Practices –Richard Tibbs / Edward Oakes – Prentice Hall – 2005 Linux Firewalls – 2 nd ed. –Robert Siegler – New Riders Publishing – 2002 Guide to Firewalls and Network Security –Greg Holden – Thomson/Course Technology – 2004 EBtables/IPtables Interaction on a bridge - 2003 –ebtables.sourceforge.net/br_fw_ia/br_fw_ia.html Red Hat Fedora Linux Secrets –Naba Barkakati – Wiley - 2005

66. cs490ns - cotter66 Summary What is a firewall? Architectures –Stand Alone / application / proxy –Personal / host based –Gateway / packet filters –Enterprise / hardware Packet Filtering concepts Packet Forwarding Roles –Bastion –DMZ EBtables