Cisco Updated 400-007 Exam Questions and Answers by freja

Loop Guardis designed to protect againstSTP loop conditionsthat may occur whenBPDUs are unexpectedly missingon a point-to-point link. This is especially relevant in cases where UDLD (Unidirectional Link Detection) might not detect the problem quickly enough. When BPDUs are absent, a switch might erroneously assume that the link is safe to forward, potentially leading to atemporary Layer 2 loop.

UsingLoop Guardensures that a port moves into aloop-inconsistentstate instead of forwarding traffic if BPDUs are missing, effectively stopping a loop before it forms. This makes it acomplementary mechanism to UDLD, which focuses on detecting unidirectional links at the physical layer, not STP control plane failures.

This recommendation aligns with CCDE v3.1 best practices forresilient Layer 2 designs, which emphasize using multiple mechanisms in tandem to proactively prevent failure conditions before traffic is impacted.

Why other options are incorrect:

A. Root Guard: Prevents an unauthorized switch from becoming the root bridge but doesn ' t protect against missing BPDUs.

B. BPDU Guard: Used mainly on access ports to prevent BPDU reception; not intended for core loop prevention.

D. BPDU Filtering: Suppresses BPDU exchange entirely, which increases loop risk and is not suited for loop mitigation.

B (Use only secure protocols): Management and administrative access to Internet edge routers must use secure protocols (SSH, SNMPv3, HTTPS) to prevent interception or unauthorized access.

E (Restrict administrative access): Limiting administrative access via interface ACLs and clear login banners ensures that only authorized personnel can access the system, satisfying compliance and security requirements.

Other options explained:

A: Filtering infrastructure IP space is good hygiene but not directly related to compliance.

C: Logging is valuable for operations and incident response but not a compliance control by itself.

D: EBGP advertisements relate to routing policy, not compliance regulation.

When both networks use overlapping private IP addresses, a single Cisco IOS NAT router can handle bidirectional NAT with dynamic NAT (overload). However, it requires careful configuration using:

Two distinct NAT pools: One for traffic sourced from side A, and one for traffic sourced from side B.

ip nat inside source and ip nat outside source commands with the overload keyword.

Interfaces must be properly defined with ip nat inside and ip nat outside to reflect traffic directionality.

Option D is correct because it explicitly reflects the requirement to use two different NAT pools for overload in both directions, which ensures proper address translation and session tracking.

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