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Question 680
A Catalyst access port is configured for a maximum of one secure MAC address with port-security violation mode shutdown. The second, unauthorized MAC appears; `show port-security interface Gi1/0/12` reports Secure-shutdown and a violation count of one. What does this state mean?
- The port has hit its security policy and been shut down by port security, not merely an IP routing failure
- The device has successfully learned two secure MACs and continues forwarding by default
- The trunk native VLAN mismatch alone is proven by the security violation count
- The switch has entered ordinary STP discarding state because a root BPDU was received
Explanation
Correct Answer
A:A new source MAC beyond the configured limit triggers a violation; shutdown mode disables the secure port, and the violation counter corroborates the cause.
Incorrect Answers
B:A one-address limit is violated by the second unauthorized MAC, so the observed Secure-shutdown status cannot mean unrestricted forwarding.
C:The port-security counter reports a MAC-security limit event rather than proving a native VLAN tagging mismatch.
D:Spanning-tree role/state is a different control plane; the displayed port-security status and count directly identify MAC-security enforcement.
Question 681
The DHCP server is connected to a trusted uplink, but client ports should never be allowed to originate server-type DHCP messages. How should ordinary host-facing ports be classified for DHCP snooping?
- Keep client-facing DHCP snooping ports untrusted
- Mark all host access ports trusted to avoid blocking legitimate DHCP replies
- Disable DHCP snooping on the VLAN so the only server cannot be blocked
- Move the trusted flag from the server uplink onto each endpoint port
Explanation
Correct Answer
A:Untrusted ports reject server-type DHCP replies under DHCP snooping policy.
Incorrect Answers
B:Ordinary clients should be untrusted so unauthorized server-type offers/ACKs arriving there can be dropped.
C:Without snooping, rogue DHCP responses from a client port are no longer filtered by trust.
D:Trust should apply to the authorized server path, not arbitrary hosts that might impersonate DHCP service.
Question 682
A Catalyst switch has DHCP snooping enabled for VLAN 40, and a laptop has just obtained a lease. Before requiring Dynamic ARP Inspection on the VLAN, the operator wants evidence of the learned client IP, MAC, VLAN and switchport. Which command should be used?
- show spanning-tree vlan 40
- show ip dhcp snooping binding
- show etherchannel summary
- show ip route ospf
Explanation
Correct Answer
B:`show ip dhcp snooping binding` displays learned dynamic IP-to-MAC mappings with VLAN and ingress interface details. These entries can provide trust data to DAI on untrusted ports.
Incorrect Answers
A:Spanning-tree output shows Layer 2 topology and forwarding state but not DHCP snooping address bindings.
C:EtherChannel summary reports link aggregation membership and status rather than DHCP leases.
D:OSPF RIB output lists dynamic routes, not the DHCP client binding table.
Question 683
A printer on VLAN 30 uses a manually assigned IPv4 address and MAC, so it has no DHCP snooping lease binding. Dynamic ARP Inspection is enabled on the untrusted access port. How can its legitimate ARP packets be validated without trusting that entire port?
- Mark the printer's access port trusted for all ARP packets regardless of sender identity
- Turn off DAI for the whole VLAN and accept ARP packets without source validation
- Add a standard IP packet-filter ACL that matches only TCP port 9100, without any ARP inspection binding
- Configure an ARP ACL permitting the printer's exact IP/MAC pair and apply it to VLAN 30's DAI policy
Explanation
Correct Answer
D:Cisco DAI supports user-defined ARP ACL entries for non-DHCP static hosts, such as permit ip host ... mac host ..., applied with ip arp inspection filter ... vlan 30.
Incorrect Answers
A:A trusted DAI port bypasses validation for all received ARP packets and weakens protection on a user-controlled access interface.
B:Disabling DAI for the VLAN removes ARP spoofing checks instead of accommodating a statically addressed host securely.
C:An IPv4 TCP ACL operates at IP/transport matching; ARP is a different EtherType and needs a compatible DAI binding source or ARP ACL.
Question 684
A malicious client floods DHCPDISCOVER packets at high rate on an untrusted access port, overwhelming the DHCP infrastructure. Which supported DHCP snooping per-port rate control mitigates this?
- Trust the flooding client’s port so its DHCP packets avoid the rate limiter
- Use only static default routes to redirect DHCP packets away from the switch
- Apply supported DHCP snooping message rate limits
- Use DAI instead of DHCP snooping message-rate enforcement
Explanation
Correct Answer
C:Rate limiting mitigates DHCP message floods on untrusted interfaces.
Incorrect Answers
A:Trusting the attacker-controlled edge port broadens its DHCP authority and is not the requested flood limit.
B:Routing paths do not bound the rate of Layer 2 DHCP broadcast requests arriving on the untrusted edge.
D:DAI protects ARP integrity; it is not the DHCPDISCOVER rate limiter specified.
Question 685
An access switch port is errdisabled after a MAC limit violation; the operator wants the specific violation counter and current secure-port state. Which port-security interface command supplies that data?
- Run show interfaces counters errors and infer the secure-port violation number
- Run show mac address-table dynamic without a port-security view
- Inspect show port-security interface counters
- Run show ip dhcp snooping binding and assume it describes port security violation state
Explanation
Correct Answer
C:Violation indicators reveal port-security learning beyond allowed MAC limits.
Incorrect Answers
A:Physical CRC/error counters do not give port-security learned count, secure-port state or violation total.
B:MAC learning alone does not show port-security enforcement state and violation counters.
D:The snooping binding table maps DHCP/IP/MAC/port, not the secure-port violation counter the question asks for.
Question 686
A branch workstation should have its learned secure MAC address persist across restart after an administrator saves the configuration. Which sticky-MAC port-security mechanism supports this behavior?
- Use dynamically learned secure MACs only and assume they are always saved to startup configuration
- Configure switchport port-security maximum 1 without enabling sticky learning
- Choose port-security violation restrict without any sticky configuration
- Use appropriately configured sticky MAC port security and save configuration
Explanation
Correct Answer
D:Sticky learning can convert dynamically learned MACs into retained secure entries.
Incorrect Answers
A:Ordinary dynamic entries expire and are not automatically retained after restart unless sticky learned entries are saved.
B:A maximum limits count but does not by itself persist the dynamically learned address as a saved sticky entry.
C:Restrict is a violation action; it does not automatically make the learned MAC persist across reboots.
Question 687
A secure access port learns an unauthorized source MAC. Company policy requires the violating frames to be discarded and violation counters or notifications to continue, but the interface must stay operational for the approved station. Which Cisco port-security action fits?
- Set port-security violation restrict mode
- Set port-security violation shutdown mode
- Set port-security violation protect mode without logging/counting requirements
- Disable port security and rely only on ordinary source MAC learning
Explanation
Correct Answer
A:Restrict drops offending frames while keeping the port up and records/reports violations according to supported platform behavior.
Incorrect Answers
B:Shutdown places a violating port into an error-disabled state, disconnecting even its legitimate authorized endpoint until recovery.
C:Protect also drops unauthorized source MAC traffic but generally does not increment or report the same violation notifications requested here.
D:With no port security, the access switch ordinarily learns source MACs without applying the configured maximum and violation action.
Question 688
A Cisco Catalyst access port allows one authorized MAC address and uses port security. The security policy requires a second unauthorized MAC to place the whole port in the secure-shutdown/errdisabled state rather than merely drop the new frame while remaining up. Which violation action is appropriate?
- restrict, which drops violating frames but retains interface forwarding state
- protect, which silently discards unauthorized source traffic
- Increase the maximum secure MAC count to 2
- Use shutdown violation mode
Explanation
Correct Answer
D:Port-security violation mode shutdown takes the port out of service when the secure-MAC limit is violated, in contrast to restrict or protect modes that can keep the interface active.
Incorrect Answers
A:Restrict prevents traffic from unauthorized MAC addresses and counts or logs violations, but does not shut the entire port as requested.
B:Protect typically drops unauthorized MAC traffic without bringing down the full interface, unlike the requested shutdown policy.
C:Raising the limit allows the previously unauthorized second address and defeats the requirement for immediate port shutdown.
Question 689
An auditor wants a list of secured MAC addresses, their VLANs and associated physical ports rather than only summary counters. Which port-security address display is most direct?
- Run show port-security address
- Use show port-security interface for counters alone without the full secure MAC address list
- Use show ip arp and treat IP-to-MAC neighbor mappings as secure port entries
- Use show vlan brief as a list of securely learned MAC addresses
Explanation
Correct Answer
A:The command lists secure MAC addresses and their associated ports.
Incorrect Answers
B:The interface view can show state and counts but does not directly list all secure MAC/VLAN/port entries the auditor requests.
C:ARP neighbor cache does not indicate which MACs are actually secured by port-security on each switchport.
D:VLAN membership shows interfaces and VLANs, not the port-security secure MAC address inventory.
Question 690
A Catalyst 9300 switch has Dynamic ARP Inspection enabled on VLAN 25, and an untrusted access port legitimately sends a short burst of 80 ARP packets per second. The IP/MAC bindings are valid, but the port enters err-disabled state. The untrusted port uses the default DAI rate limit. Which independent DAI protection explains the shutdown?
- DHCP snooping permanently blocks every host that uses a static IPv4 configuration even when the ARP bindings are valid
- ARP ACLs automatically deny every request after 15 packets, even on a trusted interface with unlimited ARP rate
- The per-interface DAI ARP packet-rate limit is exceeded (normally 15 pps on untrusted ports), causing err-disable
- PortFast detects repeated legitimate ARP transmissions and automatically converts the interface into a spanning-tree blocking port
Explanation
Correct Answer
C:Cisco Catalyst DAI rate-limits incoming ARP on untrusted interfaces to 15 packets per second by default; exceeding that limit causes the switch to error-disable the interface, even when individual ARP identity bindings are otherwise acceptable.
Incorrect Answers
A:DHCP snooping is not itself a mandatory prohibition on all statically configured hosts; DAI binding policy and packet-rate handling are separate checks.
B:An ARP ACL governs whether ARP claims match its configured policy. DAI rate limiting is a separate limit and trusted ports are not limited by the default untrusted rate.
D:PortFast accelerates STP edge forwarding behavior and does not implement DAI ARP packet-rate enforcement.
Cisco Certified Network Associate (CCNA) (200-301) Practice Tests