A. To ensure the router has the correct time when generating its private/public key pairs.
B. To ensure the router has the correct time when checking certificate validity from the remote peers
C. To ensure the router time is sync with the remote peers for encryption keys generation
D. To ensure the router time is sync with the remote peers during theDH exchange
E. To ensure the router time is sync with the remote peers when generating the cookies during IKE phase 1

A. The FTP server sends back an acknowledgment （ACK） to the client
B. The FTP server allocates a port touse for the data channel and transmit that port number to the client
C. The FTP server opens the data channel to the client using the port number indicated by the client
D. The FTP client opens the data channel to the FTP server on Port 20
E. The FTP client opens the datachannel to the FTP server on Port 21

A. RC4 is a stream cipher
B. Stream ciphers require padding
C. AES is a block cipher
D. DES and 3DES are stream ciphers
E. AES is a stream cipher
F. AES， DES， and 3DES can be used as HMAC algorithms

A. MD5 produces a 160-bit result.
B. SHA-256 is an extension to SHA-1 with a longer output.
C. MD5 takes more CPU cycles to compute than SHA-1.
D. Changing1 bit of the input to SHA-1 changes 1 bit of the output.
E. SHA-1 is stronger than MD5 because it can be used with a key to prevent modification.

A. decrypts the received MAC using a secret key
B. compares the computed MAC vs. the MAC received
C. authenticate the receivedmessage using the sender’s public key
D. look up the sender’s public key
E. extracts the MAC from the receivedmessage thenencrypts the received message with a secret keyto producethe MAC
F. Computes the MAC using the receivedmessage and a secret key as inputs to the hash function

A.An irreversible fast encryption method
B.A reversible fast encryption method
C.A reversible value computed from a piece of data and used to detect modifications
D.An irreversible value computed froma piece of data and used to detect modifications
E.A table inwhich values are stored for efficient retrieval.

A. enables IOS to copy the ToS field from the inner （original） IPheader to theouter tunnel IP header
B. enables IOS to make a copy of the inner （original） IP header and to run a QoS classification before encryption， based on fields in the inner IP header.
C. enables IOS to classify packets based on the ToS field in the inner （original） IP header
D. enables IOS to classify packets based on the ToS field in the outer tunnel IP header
E. enables the IOS classification engine to only see a single encrypted and tunneledflow to reduce classification complexity

A.Asymmetric ciphers use pre-shared keys
B.Symmetric ciphers are faster to compute
C.Asymmetric ciphers are faster to compute
D.Asymmetric ciphers use public and private

A. policy based routing （PBR）
B. unicast reverse path forwarding （uRPF）
C. lock and keyACL
D. RFC 1918filtering
E. IP source routing

A. Man-in-themiddle attack
B. Spoof attack
C. Land.C attack
D. Buffer Overflow
E. Day zero attack
F. Trojan Horse