Which of the following are features of IPsec transport mode? (Choose three.)
A . IPsec transport mode is used between end stations
B . IPsec transport mode is used between gateways
C . IPsec transport mode supports multicast
D . IPsec transport mode supports unicast
E . IPsec transport mode encrypts only the payload
F . IPsec transport mode encrypts the entire packet
Answer: A,D,E
Explanation:
+ IPSec Transport mode is used for end-to-end communications, for example, for communication between a client and a server or between a workstation and a gateway (if the gateway is being treated as a host). A good example would be an encrypted Telnet or Remote Desktop session from a workstation to a server.
+ IPsec supports two encryption modes: Transport mode and Tunnel mode. Transport mode encrypts only the data portion (payload) of each packet and leaves the packet header untouched. Transport mode is applicable to either gateway or host implementations, and provides protection for upper layer protocols as well as selected IP header fields.
Source: http://www.firewall.cx/networking-topics/protocols/870-ipsec-modes.html http://www.cisco.com/c/en/us/td/docs/net_mgmt/vpn_solutions_center/20/ip_security/provisioning/guide/ IPsecPG1.html
Generic Routing Encapsulation (GRE) is often deployed with IPsec for several reasons, including the following:
+ IPsec Direct Encapsulation supports unicast IP only. If network layer protocols other than IP are to be supported, an IP encapsulation method must be chosen so that those protocols can be transported in IP packets.
+ IPmc is not supported with IPsec Direct Encapsulation. IPsec was created to be a security protocol between two and only two devices, so a service such as multicast is problematic. An IPsec peer encrypts a packet so that only one other IPsec peer can successfully perform the de-encryption. IPmc is not compatible with this mode of operation.
Source: https://www.cisco.com/application/pdf/en/us/guest/netsol/ns171/c649/ ccmigration_09186a008074f26a.pdf
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