HPE FlexNetwork 10500 Series Configuration Manual page 283

Enlarging network scope
Figure 103 Network diagram
Device A
Host A
In an IP network, the maximum TTL value of a packet is 255. If two devices have more than 255 hops
in between, they cannot communicate with each other. By using a GRE tunnel, you can hide some
hops to enlarge the network scope. As shown in
and Device D) of the GRE tunnel are counted in hop count calculation. Therefore, there are only
three hops between Host A and Host B.
Constructing VPN
Figure 104 Network diagram
As shown in
Using a GRE tunnel can connect the two VPN sites across the WAN.
Operating with IPsec
Figure 105 Network diagram
Device A
Corporate
intranet
As shown in
Packets (for example, routing protocol packets, voice data, and video data) are first encapsulated
with GRE and then with IPsec. GRE over IPsec delivers the following benefits:
•
Improves transmission security.
GRE tunnel
IP network
Device B
IP network
VPN 1
Site 1
Device A
Figure 104, Site 1 and Site 2 both belong to VPN 1 and are located in different cities.
Internet
IPsec tunnel
GRE tunnel
Figure 105, GRE can be used together with IPsec to form a GRE over IPsec tunnel.
Device D
IP network
Device C
Figure 103, only the tunnel-end devices (Device A
GRE tunnel
Device B
WAN
Remote office
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Host B
VPN 1
Site 2
Device B
network