mediumMultiple Choice
300-410 Practice Question: Runs the following command on Router R1: R1# show…
A network engineer runs the following command on Router R1:
R1# show crypto ipsec sa peer 10.1.1.2
interface: Tunnel0
Crypto map tag: VPN-MAP, local addr 10.1.1.1protected vrf: (none) local ident (addr/mask/prot/port): (10.1.1.0/255.255.255.0/0/0) remote ident (addr/mask/prot/port): (192.168.1.0/255.255.255.0/0/0) current_peer 10.1.1.2 port 500 PERMIT, flags={origin_is_acl,} #pkts encaps: 100, #pkts encrypt: 100, #pkts digest: 100 #pkts decaps: 0, #pkts decrypt: 0, #pkts verify: 0 #send errors 0, #recv errors 0
Based on this output, what is the problem?
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 remote peer is not sending traffic back; check routing on the remote router.
The outbound packet count (encaps) is 100, but inbound (decaps) is 0. This suggests that traffic is being sent through the tunnel but no responses are being received, possibly due to a routing issue on the remote side or a firewall blocking return traffic.
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 tunnel is working correctly; all packets are being encrypted and decrypted.
Why it's wrong here
Encapsulation succeeds, but decaps, decrypt and verify all remain zero, so return traffic is not being received or processed. Claiming the tunnel works ignores this asymmetry. This option would be correct only if both encaps and decaps counters incremented, indicating bidirectional encrypted traffic.
- ✓
The remote peer is not sending traffic back; check routing on the remote router.
Why this is correct
Encapsulation counters increment while decapsulation stays at zero, proving R1 sends ESP but receives nothing. The tunnel and ACLs are fine; the remote peer is either not routing return traffic into the tunnel or lacks a matching policy, so its routing must be checked.
- ✗
The local crypto ACL is misconfigured; it is not matching traffic.
Why it's wrong here
The local ident 10.1.1.0/24 matches the local address and 100 packets were encapsulated, proving the ACL matched and encryption occurred. The zero decaps counters indicate no return traffic arrived. A misconfigured ACL would show no encaps increments, which is not the case here.
- ✗
The IPsec SA is not established; the tunnel is down.
Why it's wrong here
The SA is established: encaps, encrypt and digest counters all increment, and PERMIT flags appear. The absence of decaps, decrypt and verify counters shows inbound traffic never arrived. A down SA would display no security associations or zero encaps counters, which this output contradicts.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
Related to this question
Learn chapter
Device Management and Network Monitoring (SNMP, Syslog, NetFlow)
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.