D-Link DFL-260E User Manual for DFL-260E - Page 121
Using GRE, GRE Security and Performance, Setting Up GRE, IP Address, Remote Network, Remote Endpoint
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3.4.5. GRE Tunnels Chapter 3. Fundamentals GRE does not provide any security features but this means that its use has extremely low overhead. Using GRE GRE is typically used to provide a method of connecting two networks together across a third network such as the Internet. The two networks being connected together communicate with a common protocol which is tunneled using GRE through the intervening network. Examples of GRE usage are: • Traversing network equipment that blocks a particular protocol. • Tunneling IPv6 traffic across an IPv4 network. • Where a UDP data stream is to be multicast and it is necessary to transit through a network device which does not support multicasting. GRE allows tunneling though the network device. GRE Security and Performance A GRE tunnel does not use any encryption for the communication and is therefore not, in itself, secure. Any security must come from the protocol being tunneled. The advantage of GRE's lack of encryption is the high performance which is achievable because of the low traffic processing overhead. The lack of encryption can be acceptable in some circumstances if the tunneling is done across an internal network that is not public. Setting Up GRE Like other tunnels in NetDefendOS such as an IPsec tunnel, a GRE Tunnel is treated as a logical interface by NetDefendOS, with the same filtering, traffic shaping and configuration capabilities as a standard interface. The GRE options are: • IP Address This is the IPv4 address of the inside of the tunnel on the local side. This cannot be left blank and must be given a value. The specified IP address is then used for the following: i. An ICMP Ping can be sent to this tunnel endpoint. ii. Log messages related to the tunnel will be generated with this IP address as the source. iii. If NAT is being used then it will not be necessary to set the source IP on the IP rule that performs NAT on traffic going through the tunnel. This IP address will be used as the source address for NAT. • Remote Network The remote network which the GRE tunnel will connect with. • Remote Endpoint This is the IPv4 address of the remote device which the tunnel will connect with. • Use Session Key A unique number can optionally be specified for the tunnel. This allows more than one GRE tunnel to run between the same two endpoints. The Session Key value is used to distinguish 121