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IPsec Site-to-Site VPN →mediumMultiple ChoiceObjective-mapped

300-410 IPsec Site-to-Site VPN Practice Question

This 300-410 practice question tests your understanding of ipsec site-to-site vpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A network engineer runs the following command to troubleshoot an IPsec Site-to-Site VPN issue:

R1# show crypto ipsec sa detail

interface: Tunnel0
    Crypto map tag: CMAP, local addr 192.168.1.1

protected vrf: (none) local ident (addr/mask/prot/port): (192.168.1.0/255.255.255.0/0/0) remote ident (addr/mask/prot/port): (192.168.2.0/255.255.255.0/0/0) current_peer 192.168.2.2 port 500 PERMIT, flags={origin_is_acl,} #pkts encaps: 0, #pkts encrypt: 0, #pkts digest: 0 #pkts decaps: 0, #pkts decrypt: 0, #pkts verify: 0 #pkts compressed: 0, #pkts decompressed: 0 #pkts not compressed: 0, #pkts compr. failed: 0 #pkts not decompressed: 0, #pkts decompress failed: 0 #send errors 0, #recv errors 0

local crypto endpt.: 192.168.1.1, remote crypto endpt.: 192.168.2.2 path mtu 1500, ip mtu 1500, ip mtu idb Serial0/0/0 current outbound spi: 0x0(0) PFS (Y/N): N, DH group: none

inbound esp sas: spi: 0x0(0) transform: esp-3des esp-sha-hmac , in use settings ={Tunnel, } conn id: 0, flow_id: 0, sibling_flags 80000000, crypto map: CMAP sa timing: remaining key lifetime (k/sec): (0/0) IV size: 8 bytes replay detection support: N

outbound esp sas: spi: 0x0(0) transform: esp-3des esp-sha-hmac , in use settings ={Tunnel, } conn id: 0, flow_id: 0, sibling_flags 80000000, crypto map: CMAP sa timing: remaining key lifetime (k/sec): (0/0) IV size: 8 bytes replay detection support: N

What does this output indicate?

Question 1mediummultiple choice
Read the full VPN explanation →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The IPsec SA is in a pending state; the SPI is 0, meaning the SA negotiation is incomplete or the SA has been deleted.

The output shows SPI values of 0x0 for both inbound and outbound ESP SAs, with zero packet encapsulation and encryption counts. This indicates that the IPsec Security Association (SA) negotiation is incomplete or the SA has been deleted, as a valid SA would have a non-zero SPI and active packet counters. The 'current_peer' and crypto map are present, but the SA is not operational.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    The IPsec SA is fully established and encrypting traffic.

    Why it's wrong here

    The zero packet counts and zero SPI indicate no traffic has been encrypted.

  • ✓

    The IPsec SA is in a pending state; the SPI is 0, meaning the SA negotiation is incomplete or the SA has been deleted.

    Why this is correct

    SPI of 0 and zero lifetime indicate the SA is not active; it may have been cleared or never completed.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    The IPsec SA is using PFS, which is causing the SA to be rekeyed frequently.

    Why it's wrong here

    PFS is set to N, so that is not the issue.

  • ✗

    The crypto map is not applied to the interface, so the SA is not used.

    Why it's wrong here

    The crypto map is shown as applied to Tunnel0, so it is applied.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a crypto map present in the output means the SA is active, but the SPI of 0x0 and zero packet counters are the definitive indicators of an incomplete or deleted SA.

Trap categories for this question

  • Command / output trap

    The crypto map is shown as applied to Tunnel0, so it is applied.

Detailed technical explanation

How to think about this question

In IPsec, the Security Parameter Index (SPI) is a unique identifier for each SA, and a value of 0x0 typically means the SA has not been negotiated or has been cleared. The 'show crypto ipsec sa detail' command reveals SA lifetimes, transform sets, and PFS status; here, the remaining key lifetime of (0/0) further confirms the SA is not active. This often occurs when IKE phase 2 fails due to mismatched proxy identities, transform sets, or firewall issues blocking UDP port 500/4500.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 300-410 question test?

IPsec Site-to-Site VPN — This question tests IPsec Site-to-Site VPN — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The IPsec SA is in a pending state; the SPI is 0, meaning the SA negotiation is incomplete or the SA has been deleted. — The output shows SPI values of 0x0 for both inbound and outbound ESP SAs, with zero packet encapsulation and encryption counts. This indicates that the IPsec Security Association (SA) negotiation is incomplete or the SA has been deleted, as a valid SA would have a non-zero SPI and active packet counters. The 'current_peer' and crypto map are present, but the SA is not operational.

What should I do if I get this 300-410 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 24, 2026

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