H3C Technologies H3C SecPath F1000-E - Manual (Page 4)

3
GRE Security Options
For the purpose of tunnel security, GRE provides two options: tunnel interface key and end-to-end
checksum.
According to RFC 1701,
• If the Key Present field of a GRE packet header is set to 1, the Key field will carry the key for the
receiver to authenticate the source of the packet. This key must be the same at both ends of a tunnel.
Otherwise, packets delivered over the tunnel will be discarded.
• If the Checksum Present bit of a GRE packet header is set to 1, the Checksum field contains valid
information. The sender calculates the checksum for the GRE header and the payload and sends
the packet containing the checksum to the peer. The receiver calculates the checksum for the
received packet and compares it with that carried in the packet. If the checksums are the same, the
receiver considers the packet intact and continues to process the packet. Otherwise, the receiver
discards the packet.
GRE Applications
GRE supports these types of applications:
• Communication between local networks through a single-protocol backbone
• Scope enlargement of a hop-limited protocol
• VPN creation by connecting discontinuous subnets
• GRE-IPsec tunnel application
Communication between local networks through a single-protocol backbone
Figure 4 Communication between local networks through a single-protocol backbone
In the example shown in
Figure 4 , Team 1 and Team 2 are local networks running IP. Through the GRE
tunnel between Device A and Device B, Team 1 can communicate with Team 2.