SYSTEM ADMINISTRATION EXAM
PREPARATION QUESTIONS WITH FULL
RATIONALES 2026
▶ CoS. Answer: Class of Service:
A method of managing traffic in a network by assigning different levels of
priority to different types of traffic. This allows network administrators to
ensure that more important or time-sensitive data, such as voice or video,
receives preferential treatment over less critical traffic, like email or file
downloads.
▶ Error: CRYPTO-4-IKMP_BAD_MESSAGE: IKE message from x.x.x.x
failed its sanity check or is malformed.
What is the most likely cause of this error?
A) Network latency causing packet loss
B) Incorrect NAT configuration
C) Mismatched Pre-Shared Keys (PSKs) on the peer routers
D) Unsupported encryption algorithm. Answer: Correct Answer: C)
Mismatched Pre-Shared Keys (PSKs) on the peer routers
▶ Error: CRYPTO-6-IKMP_NO_SA: IKE message from x.x.x.x has no SA
and is not an initialization offer.
What is the most likely cause of this error?
A) The VPN policy parameters are mismatched between the peers
B) The PSKs are mismatched on the peer routers
C) The certificate is not trusted
D) The peer device is unreachable. Answer: Correct Answer: A) The VPN
policy parameters are mismatched between the peers
▶ Error: CRYPTO-4-IKMP_INVALID_PAYLOAD_TYPE: Invalid payload
type 20 received from x.x.x.x.
What is the most likely cause of this error?
A) Mismatch in IKE policy configurations
, B) Expired certificates
C) Incorrect NAT-T configuration
D) Network congestion. Answer: Correct Answer: A) Mismatch in IKE
policy configurations
▶ Error: CRYPTO-6-IKMP_SA_NOTFOUND: IKE message from x.x.x.x
failed its sanity check or is malformed.
What is the most likely cause of this error?
A) Incorrect access control lists (ACLs)
B) High CPU utilization on the peer router
C) Outdated firmware on one of the devices
D) Mismatch in Phase 1 parameters like encryption algorithms. Answer:
Correct Answer: D) Mismatch in Phase 1 parameters like encryption
algorithms
▶ Error: CRYPTO-6-IKMP_NO_CERT: No certificate found for the peer
x.x.x.x.
What is the most likely cause of this error?
A) The certificate on the peer device has expired
B) Incorrect pre-shared keys
C) Network interface is down
D) Incompatible Diffie-Hellman group. Answer: Correct Answer: A) The
certificate on the peer device has expired
▶ Error: CRYPTO-4-IKMP_NO_PEER_CERT: Received a certificate from
x.x.x.x which is not trusted.
What is the most likely cause of this error?
A) Inconsistent routing paths
B) Mismatched encryption algorithms
C) The peer's certificate authority (CA) is not trusted
D) Incorrect firewall rules blocking IKE traffic. Answer: Correct Answer: C)
The peer's certificate authority (CA) is not trusted
▶ Error: CRYPTO-4-IKMP_INVALID_EXCH_TYPE: Invalid exchange type
243 from x.x.x.x.
What is the most likely cause of this error?
PREPARATION QUESTIONS WITH FULL
RATIONALES 2026
▶ CoS. Answer: Class of Service:
A method of managing traffic in a network by assigning different levels of
priority to different types of traffic. This allows network administrators to
ensure that more important or time-sensitive data, such as voice or video,
receives preferential treatment over less critical traffic, like email or file
downloads.
▶ Error: CRYPTO-4-IKMP_BAD_MESSAGE: IKE message from x.x.x.x
failed its sanity check or is malformed.
What is the most likely cause of this error?
A) Network latency causing packet loss
B) Incorrect NAT configuration
C) Mismatched Pre-Shared Keys (PSKs) on the peer routers
D) Unsupported encryption algorithm. Answer: Correct Answer: C)
Mismatched Pre-Shared Keys (PSKs) on the peer routers
▶ Error: CRYPTO-6-IKMP_NO_SA: IKE message from x.x.x.x has no SA
and is not an initialization offer.
What is the most likely cause of this error?
A) The VPN policy parameters are mismatched between the peers
B) The PSKs are mismatched on the peer routers
C) The certificate is not trusted
D) The peer device is unreachable. Answer: Correct Answer: A) The VPN
policy parameters are mismatched between the peers
▶ Error: CRYPTO-4-IKMP_INVALID_PAYLOAD_TYPE: Invalid payload
type 20 received from x.x.x.x.
What is the most likely cause of this error?
A) Mismatch in IKE policy configurations
, B) Expired certificates
C) Incorrect NAT-T configuration
D) Network congestion. Answer: Correct Answer: A) Mismatch in IKE
policy configurations
▶ Error: CRYPTO-6-IKMP_SA_NOTFOUND: IKE message from x.x.x.x
failed its sanity check or is malformed.
What is the most likely cause of this error?
A) Incorrect access control lists (ACLs)
B) High CPU utilization on the peer router
C) Outdated firmware on one of the devices
D) Mismatch in Phase 1 parameters like encryption algorithms. Answer:
Correct Answer: D) Mismatch in Phase 1 parameters like encryption
algorithms
▶ Error: CRYPTO-6-IKMP_NO_CERT: No certificate found for the peer
x.x.x.x.
What is the most likely cause of this error?
A) The certificate on the peer device has expired
B) Incorrect pre-shared keys
C) Network interface is down
D) Incompatible Diffie-Hellman group. Answer: Correct Answer: A) The
certificate on the peer device has expired
▶ Error: CRYPTO-4-IKMP_NO_PEER_CERT: Received a certificate from
x.x.x.x which is not trusted.
What is the most likely cause of this error?
A) Inconsistent routing paths
B) Mismatched encryption algorithms
C) The peer's certificate authority (CA) is not trusted
D) Incorrect firewall rules blocking IKE traffic. Answer: Correct Answer: C)
The peer's certificate authority (CA) is not trusted
▶ Error: CRYPTO-4-IKMP_INVALID_EXCH_TYPE: Invalid exchange type
243 from x.x.x.x.
What is the most likely cause of this error?
