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IOS Firewall

IOS Firewall. IOS: Cisco’s Internetwork Operating System (the primary system running on Cisco’s routers) IOS Firewall: a stateful packet-filter firewall that runs on a router, providing firewall capabilities

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IOS Firewall

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  1. IOS Firewall • IOS: Cisco’s Internetwork Operating System (the primary system running on Cisco’s routers) • IOS Firewall: a stateful packet-filter firewall that runs on a router, providing firewall capabilities • CBAC: Context-Based Access Control (at the core of the IOS Firewall functionality

  2. Outline • CBAC • IOS Firewall Features • Case studies http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

  3. CBAC (Context-Based Access Control) • Implement packet filtering on a Cisco router (similar to ASA on Cisco PIX) • Three basic functionalities: • Dynamic modification of the extended access lists • To allow connections initiated from the inside • Inspection of the application/transport level protocols ~= multimedia support in PIX • Control of the number/length of sessions http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

  4. CBAC Functionality • Set up Access Control Lists to open holes for inbound access to inside servers • Set up the router to inspect outbound packets, and • Keep track of the associated sessions  i.e., a stateful packet filter http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

  5. How does IOS maintain session state information? • State Information Structure (SIS) • A SIS is created for each logical session. • The SIS uniquely identifies a connection using the IP and the port#). • When necessary, other info such as TCP connection state, TCP sequence number, etc. are also maintained. • The SIS is deleted when the associated session/connection is terminated. http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

  6. Other CBAC functionality • Out-of-sequence TCP packets are dropped. • TCP packets with invalid sequence numbers are dropped. • The reassembly of IP packets is not supported (as in PIX firewall). • Does not inspect packets originated by the IOS Firewall router. • ICMP packets are not inspected. (They are manually managed using static ACLs). • ICMP unreachable packets are ignored. • To protect against a flooding attack or unusual consumption of memory due to a large number of SISs: • when the number of SISs in the half-open state reaches a threshold, half-open SISs are deleted to accommodate a new session. • If the rate of new TCP connection requests is higher than a maximum value, half-open SISs are deleted for every new connection request. http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

  7. Features of IOS Firewall • Transport Layer Inspection • Application Layer Inspection • Filtering for Invalid Commands • Java Blocking • Safeguarding against DOS attacks • Fragment handling http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

  8. Case Study • CBAC on a router configured with NAT http://sce.uhcl.edu/yang/teaching/.../IOS Firewalls.ppt

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