Netgear ADSL Firewall Router DG834 User Manual download pdf (Page 193)

Reference Manual for the ADSL Firewall Router DG834

Virtual Private Networking D-5

202-10005-05, June 2005

Mode

SAs operate using modes. A mode is the method in which the IPSec protocol is applied to the

packet. IPSec can be used in tunnel mode or transport mode. Typically, the tunnel mode is used for

gateway-to-gateway IPSec tunnel protection, while transport mode is used for host-to-host IPSec

tunnel protection. A gateway is a device that monitors and manages incoming and outgoing

network traffic and routes the traffic accordingly. A host is a device that sends and receives

network traffic.

• Transport Mode: The transport mode IPSec implementation encapsulates only the packet’s

payload. The IP header is not changed. After the packet is processed with IPSec, the new IP

packet contains the old IP header (with the source and destination IP addresses unchanged)

and the processed packet payload. Transport mode does not shield the information in the IP

header; therefore, an attacker can learn where the packet is coming from and where it is going

to. The previous packet diagrams show a packet in transport mode.

• Tunnel Mode: The tunnel mode IPSec implementation encapsulates the entire IP packet. The

entire packet becomes the payload of the packet that is processed with IPSec. A new IP header

is created that contains the two IPSec gateway addresses. The gateways perform the

encapsulation/decapsulation on behalf of the hosts. Tunnel mode ESP prevents an attacker

from analyzing the data and deciphering it, as well as knowing who the packet is from and

where it is going.

Note: AH and ESP can be used in both transport mode or tunnel mode.

Figure D-3: Original packet and packet with IPSec ESP in Tunnel mode

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Netgear ADSL Firewall Router DG834 User Manual Page 193