Using a firewall to control traffic in networks 1 Example Network - - PowerPoint PPT Presentation

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Using a firewall to control traffic in networks 1 Example Network - - PowerPoint PPT Presentation

Jan 11, 2024 556 likes •711 views

Using a firewall to control traffic in networks 1 Example Network .35 .12 .36 .11 3.3.3.0/24 1.1.1.0/24 Rd .1 Ra .4.1 .4.4 1.1.0.0/16 Rc 2.2.2.0/24 .1 .4.2 .1 .23 Rb .47 Re .15.6 .99 1.1.2.0/24 4.4.4.0/24 .24 2 Firewall

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Using a firewall to control traffic in networks

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Example Network

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1

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Firewall on 1.1.1.12

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1

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Block Ping

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1

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Block Ping

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1 IN: protocol=ICMP; action=DROP OUT: protocol=ICMP; action=DROP

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Firewall contains rules

  • Each packet is checked against firewall rules
  • If conditions in rule are true then perform

action on that packet (eg. DROP, ACCEPT)

  • If no rules match, then perform default action
  • Multiple rules are combined to create a table
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Firewall on Router Ra

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1

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Block Access to SSH Server on .11

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1

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Block Access to SSH Server on .11

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1 FORWARD: Dst=1.1.1.11; Protocol=TCP; DstPort=22; Action=DROP

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Firewall can have different rules

  • INPUT: Applies only to packets destined to this

computer

  • OUTPUT: Applies only to packets created by

this computer

  • FORWARD: Applies only to packets going

through this computer

  • These are called chains
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Block Access to Web Servers on Network 3.3.3.0/24 for .12

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1

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Block Access to Web Servers on Network 3.3.3.0/24 for .12

1.1.1.0/24 1.1.2.0/24 1.1.0.0/16 2.2.2.0/24 4.4.4.0/24 3.3.3.0/24 .11 .12 .23 .24 .15.6 Ra Rb Rc Rd Re .99 .47 .35 .36 .1 .1 .4.4 .4.1 .4.2 .1 FORWARD: Src=1.1.1.12; Dst=3.3.3.0/24; Protocol=TCP; DstPort=80; Action=DROP

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Firewall Rules Viewed as Table

Rule Source Dest. Protocol Action 1 * 1.1.1.11:22 TCP DROP 2 1.1.1.12:* 3.3.3.0/24:80 TCP DROP Default * * * ACCEPT When packet arrives at firewall, rules are checked row-by-row. If a rule matches, the ACTION is taken and no further rules are checked. Separate tables for INPUT, OUTPUT and FORWARD chains. Firewall table for FORWARD: