H3C Technologies H3C SecPath F1000-E - Manual (Page 5)

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Scope enlargement of a hop-limited protocol such as RIP
Figure 5 Network scope enlargement
When the hop count between two terminals exceeds 15, the terminals cannot communicate with each
other. Using GRE, you can hide some hops so as to enlarge the scope of the network.
VPN creation by connecting discontinuous subnets
Figure 6 Connect discontinuous subnets with a tunnel to form a VPN
In the example as shown in
Figure 6 , subnets Group 1 and Group 2 are deployed in different cities. They
can constitute a trans-WAN virtual private network (VPN) through the tunnel.
GRE-IPsec tunnel application
Figure 7 GRE-IPsec tunnel application
Internet
Corporate
intranet
Remote office
network
Device A Device B
GRE tunnel
IPSec tunnel
GRE can work with IPsec, allowing data packets like routing protocol, voice, and video packets to be
encapsulated by GRE and then encrypted by IPsec to improve security of data transmission in a tunnel.