Initial Configuration ISP Router Version 12.3(4)T7! Hostname
Initial Configuration ISP Router version 12.3(4)T7 ! hostname ISP_Router ! interface FastEthernet0/0 ip address 200.100.0.1 255.255.255.0 ! interface FastEthernet1/0 ip address 200.100.40.1 255.255.255.0 ! interface Serial0/0 ip address 200.100.10.1 255.255.255.0 ! interface Serial0/1 ip address 200.100.20.1 255.255.255.0 ! router rip network 200.100.0.0 network 200.100.10.0 network 200.100.20.0 network 200.100.40.0 ! line con 0 line aux 0 line vty 0 4 password cisco line vty 5 15 password cisco ! end
Explain the meaning of the "three P's" best practice rule to create ACL in routers. Explain the difference between the following two access-list commands: a) access-list 101 permit tcp any any eq 80 and b) access-list 101 permit tcp any eq 80 any. Describe well-known, registered, and ephemeral UDP/TCP ports. Analyze what is wrong with ACL 105: access-list 105 permit tcp any any access-list 105 deny tcp host 201.141.0.3 any. Identify the well-known TCP port used by Oracle Database (sql net) server. Justify why the ISP network engineers chose to create an extended ACL and apply it inbound on F0/0 for securing responses from the Oracle server to specific hosts within Dallas and Chicago networks. Provide the necessary configuration commands to add and apply the appropriate ACL to the ISP router, based on the initial configuration provided.
Paper For Above instruction
The effective management of network security relies heavily on the implementation of access control policies, among which Access Control Lists (ACLs) are fundamental. A critical best practice for creating ACLs in routers is encapsulated by the "three P's" rule: "Per-Protocol, Per-Interface, Per-Traffic Direction." This guideline ensures that each ACL is specifically tailored to handle one protocol, applied on a single interface, and designated for either inbound or outbound traffic. By adhering to the "three P's," network administrators can maintain clear, manageable, and precise ACLs that minimize unintended access or disruptions. This structured approach also facilitates troubleshooting and future modifications, as each ACL's purpose and scope are explicitly defined.
The first difference between the two access-list commands—"access-list 101 permit tcp any any eq 80" and "access-list 101 permit tcp any eq 80 any"—lies in their source and destination fields. The command "permit tcp any any eq 80" permits TCP traffic from any source IP address to any destination IP address where the destination port is equal to 80, which is commonly used for HTTP web traffic. Conversely, the command "permit tcp any eq 80 any" restricts the source to a specific port (port 80), typically representing an HTTP server, with the destination being any IP address. This command pattern is less common and usually intended to specify traffic originating from a specific port, which is less relevant for filtering incoming client requests but could be used in specific scenarios.
Understanding port assignment is crucial for defining network policies. Well-known ports, assigned from 0 to 1023, are standardized for common services (e.g., port 80 for HTTP, port 443 for HTTPS). Registered ports, ranging from 1024 to 49151, are assigned to user processes and applications, such as SQL server ports or FTP. Ephemeral ports, from 49152 to 65535, are temporarily allocated for client-side communications during active sessions. Proper differentiation of these port types facilitates accurate ACL configurations and security policies.
ACL 105 presents a logical inconsistency: it starts with "permit tcp any any" followed by "deny tcp host 201.141.0.3 any." Since ACLs process rules sequentially, and "permit tcp any any" permits all TCP traffic, the subsequent deny rule becomes ineffective for packets matching it—unless ordering is changed, or specific rules are designed accordingly. To effectively deny traffic from host 201.141.0.3 while permitting all other TCP traffic, the deny rule must precede the permit rule.
The Oracle Database (sql net) server utilizes TCP port 1521, which is recognized as the well-known port for Oracle's SQL*Net protocol. This port's standardization allows for straightforward ACL creation to permit or deny database traffic as needed.
In the scenario where an ISP manages network traffic for multiple remote locations accessing an off-site Oracle database, creating an extended ACL and applying it inbound on interface F0/0 is a strategic decision. Extended ACLs offer granular filtering capabilities, allowing the administrator to specify protocols, source and destination IP addresses, and port numbers. Applying the ACL inbound close to the source aids in reducing unnecessary traffic downstream, improves security by filtering at the earliest point, and simplifies traffic management by only permitting relevant responses from the database server to designated hosts within Dallas and Chicago LANs.
Based on the initial configuration of the ISP router, the following commands demonstrate the creation and application of an extended ACL to permit SQL traffic from specific servers and restrict all other TCP traffic from the Public Server. First, the ACL must be created in global configuration:
Router# configure terminal
Router(config)# access-list 100 permit tcp host 200.100.0.2 host 200.100.10.10 eq 1521
Router(config)# access-list 100 permit tcp host 200.100.0.2 host 200.100.20.10 eq 1521
Router(config)# access-list 100 permit tcp host 200.100.0.2 host 200.100.30.10 eq 1521
Router(config)# access-list 100 permit tcp host 200.100.0.2 host 200.100.40.10 eq 1521
Router(config)# access-list 100 deny tcp host 200.100.0.2 any
Router(config)# access-list 100 permit ip any any
Next, the ACL is applied inbound on interface FastEthernet0/0 to filter traffic coming from the public network destined for the database server:
Router(config)# interface FastEthernet0/0
Router(config-if)# ip access-group 100 in
This configuration ensures that only responses from the Oracle server to the designated hosts are allowed through, effectively securing the database against unauthorized access. The order of the rules is crucial—specific permit rules must come first, followed by deny rules, and a permit ip any any rule at the end to allow all other traffic as permitted by policy.
In summary, the proper application of ACL best practices—using the "three P's," understanding port classifications, and designing rules in logical order—is essential for robust network security. Extended ACLs provide necessary granularity for complex policies, especially in environments such as database security scenarios. The precise configuration commands, tailored to the initial router setup, solidify the secure access controls needed for sensitive data handling and network integrity.