Gre - RACOM RipEX User Manual

7.5.2. GRE

Fig. 7.8: Menu GRE
■ GRE tunnel basic description
GRE (Generic Routing Encapsulation) is a tunneling protocol developed by Cisco Systems that can
encapsulate a wide variety of network layer protocols inside virtual point-to-point links over an Internet
Protocol network.
From the point of view of the transferred traffic, the GRE tunnel is one hop
There are 2 modes of GRE operation: TUN (Tunnel mode) or TAP (L2 transparent connection)
with SW bridge. RipEX implementation covers only the TUN mode
Packets passing the GRE tunnel are not protected against loss and are not encrypted.
GRE tunnel neither establishes nor maintains a connection with the peer. The GRE tunnel is
created regardless of peer status (peer need not exist at all).
GRE tunnel has it's own IP address and mask. Network defined by this address and mask con-
tains only 2 nodes – each end of the tunnel.
As the GRE tunnel adds an additional header, a lower MTU is set (1476 B) to prevent GRE
packet fragmentation. Incoming packets may be fragmented on the GRE interface.
■ GRE
GRE
List box: On, Off
Default = Off
GRE system turning On/Off
■ GRE tunnels
Every line in the "GRE tunnels" table defines one GRE tunnel. It is recommended that maximum
20 GRE tunnels are defined. The "Peer address" is a unique GRE tunnel identifier.
Peer address
Defined as the IP address for the opposite end of the GRE tunnel. It is not possible to create
multiple GRE tunnels with the same peer address. Corresponding "Peer address" on either side
of the GRE tunnel must match.
Routing to this IP address must be configured.
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Advanced Configuration
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