Lab Simulation 58 Please use the "Tasks" and "Topology" tabs to complete this lablet. Topology Connectivity between the devices has been established. IP services must be configured to complete the imp

Question

Exhibits

Explanation

This lab simulation requires configuring NAT interface roles, an NTP server with a specific stratum and source, DHCP relay and exclusions, and the complete removal of SSH configuration parameters across multiple network devices.

Approach. To correctly complete the simulation tasks, the following interactions and configurations are required:

Task 1: Define inside and outside interfaces for PAT on R2.

• Interaction: On Router R2, enter global configuration mode. Navigate to interface e0/1 and configure ip nat inside. Then, navigate to interface e0/0 and configure ip nat outside.
• Reasoning: The task states PAT uses 10.0.122.2 (R2's e0/1 IP) as the private IP and 209.165.201.6 (R2's e0/0 IP) as the public IP. Therefore, R2's interface e0/1, which connects to the private network segment (10.0.122.0/30 and subsequently VLAN 220's 10.220.10.0/24), must be designated as the ip nat inside interface. R2's interface e0/0, which connects to the public Internet, must be designated as the ip nat outside interface. This allows R2 to correctly translate private source IPs to the public IP when traffic exits to the Internet.

Task 2: Configure R2 as an NTP server.

• Interaction: On Router R2, enter global configuration mode. Configure ntp master 3. Then, configure ntp source Loopback0.
• Reasoning: The command ntp master 3 configures R2 to be an authoritative NTP server, using its own internal clock as the time source and setting its stratum level to 3, as required. The ntp source Loopback0 command ensures that NTP packets sourced by R2 use the stable IP address of its Loopback0 interface (10.2.202.2) rather than a physical interface, which provides resilience if a physical interface goes down. The task also specifies not to use ntp broadcast client or ntp multicast client and not to allow peering, which is consistent with R2 acting as an authoritative server (ntp master).

Task 3: Complete the DHCP configuration.

• Interaction 1 (Sw1 DHCP Relay): On Switch Sw1, enter global configuration mode. Access the interface VLAN 220 (e.g., interface vlan 220). Configure ip helper-address 10.0.122.2.
• Reasoning 1: DHCP requests are broadcast. Clients in VLAN 220 reside on the 10.220.10.0/24 network. Sw1 acts as the Layer 3 boundary for this VLAN (implied by its connection to R3 on VLAN 220 and its role as a switch). To forward DHCP requests from VLAN 220 clients to the DHCP server on R2, Sw1 must be configured with ip helper-address on its Switch Virtual Interface (SVI) for VLAN 220. The target IP address for the helper is R2's interface e0/1 IP (10.0.122.2), which directly connects Sw1 to R2.
• Interaction 2 (R2 DHCP Exclusion): On Router R2, enter global configuration mode. Configure ip dhcp excluded-address 10.220.10.225 10.220.10.255.
• Reasoning 2: The ip dhcp excluded-address command is used to prevent the DHCP server from assigning specific IP addresses within its configured pools. This command, applied globally on R2, ensures that the range from 10.220.10.225 through 10.220.10.255 is not handed out to DHCP clients in the 10.220.10.0/24 network, fulfilling the exclusion requirement.
• Interaction 3 (R3 DHCP Client): On Router R3, enter global configuration mode. Navigate to interface e0/0 (e.g., interface e0/0). Configure ip address dhcp. Ensure the interface is active with no shutdown.
• Reasoning 3: To verify R3 receives an IP address from DHCP, its interface e0/0, which is connected to VLAN 220, must be configured as a DHCP client. The ip address dhcp command instructs the interface to obtain its IP address, subnet mask, and other IP parameters from a DHCP server. no shutdown ensures the interface is administratively up and can participate in network communication.

Task 4: Remove SSH configuration parameters from R2.

• Interaction: On Router R2, enter global configuration mode. Configure no ip ssh version 2. Then, configure no ip ssh. Finally, remove the RSA keys using crypto key zeroize rsa (and confirm with 'yes').
• Reasoning: no ip ssh version 2 directly addresses the requirement to remove SSH Version 2 support. The no ip ssh command disables the SSH server process entirely on R2, preventing any SSH connections from being established. crypto key zeroize rsa removes the RSA key pair that is fundamental for SSH encryption. Without these keys, SSH cannot function, effectively and thoroughly removing SSH access and configuration from R2.

Common mistakes.

• common_mistake. Many common mistakes could lead to incorrect solutions for these tasks:

• Task 1 (NAT): Reversing the ip nat inside and ip nat outside commands (e.g., ip nat inside on e0/0 and ip nat outside on e0/1) would prevent PAT from working correctly because the router would expect private traffic on the public interface and vice versa. Another mistake is forgetting one of the commands or applying them to the wrong physical interfaces.

• Task 2 (NTP): Using ntp server <IP_address> instead of ntp master 3 would configure R2 as an NTP client syncing with another server, contradicting the requirement for R2 to use 'its clock as a time source'. Omitting ntp source Loopback0 means NTP packets could be sourced from a physical interface's IP, which is less stable than a loopback interface and may change if the physical interface state changes.

• Task 3 (DHCP):

  • For DHCP Relay on Sw1: Configuring ip helper-address on a physical interface (e.g., interface e0/1) instead of the SVI for VLAN 220 (e.g., interface vlan 220) would fail to forward DHCP requests from clients in that VLAN. DHCP broadcasts are handled at the Layer 3 boundary, which for a VLAN on a switch is its SVI. Using an incorrect destination IP for the helper address (e.g., the Sw1 Loopback0 IP instead of R2's directly connected interface IP) would also prevent forwarding.
  • For DHCP Exclusion on R2: Not specifying the correct or entire range (e.g., 10.220.10.225 instead of 10.220.10.225 10.220.10.255) would exclude only a single address instead of the required range. Placing the ip dhcp excluded-address command inside an ip dhcp pool configuration (which is typically a global command) might not work or could cause unexpected behavior depending on the IOS version.
  • For R3 DHCP Client: Forgetting the no shutdown command on R3's e0/0 interface would leave the interface administratively down, preventing it from sending or receiving DHCP requests and thus obtaining an IP address.

• Task 4 (SSH): Only using no ip ssh version 2 would still leave the SSH server active (potentially for SSHv1 if enabled, or generally) and wouldn't fully remove SSH access. Only configuring no transport input ssh on VTY lines would restrict SSH access to those specific lines but wouldn't disable the SSH server process itself. Not removing the crypto keys (crypto key zeroize rsa) would leave sensitive cryptographic material on the router, which is poor security practice when completely removing SSH.

Concept tested. This simulation primarily tests knowledge of:

• Network Address Translation (NAT) / Port Address Translation (PAT): Specifically, configuring ip nat inside and ip nat outside interfaces.
• Network Time Protocol (NTP): Configuring a router as an authoritative NTP server, setting its stratum, and specifying a source interface for NTP packets.
• Dynamic Host Configuration Protocol (DHCP): Configuring DHCP relay (using ip helper-address), excluding specific IP addresses from a DHCP pool, and configuring a device as a DHCP client.
• Secure Shell (SSH): Disabling specific SSH versions, removing the SSH server, and zeroizing cryptographic keys for SSH.

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