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Figure 67: Primary and Resilient Tunnels
Resilient Tunnels are used for backing-up Primary Tunnels.
Should a Primary Tunnel go out of service, the Resilient
Tunnel will automatically be used for VPN traffic.
Tunnel Switching
The switching mechanism involves time and a packet called a Heartbeat.
how tunnels are switched.
Figure 68: Tunnel Switching
Control End-point:
tunnel switching is
controlled here.
Explanation for
1. VSU
listens to VSU
A
Heartbeat Interval.
2. If VSU
realizes a dead heartbeat, it asks VSU
A
3. The number of times that VSU
Heartbeat Retry Limit.
4. If the number of requests exceeds the Heartbeat Retry Limit, VSU
a connection with VSU
5. Since VSU
VSU
. That delay is called Hold-up Time, and is configurable with VPNmanager Console.
C
Tokyo LAN
VSU
LAN
VSU
LAN
A
Figure 68
's heartbeat. The heartbeat has a configurable period called a
B
A
.
C
uses a low-speed connection, VSU
C
Primary Tunnel
High-speed
WAN
Router
A
Low-speed
Resilient Tunnel
1
2
5
6
High-speed
WAN
Router
Low-speed
4
3
for a heartbeat.
B
can make a request is configurable, and is called the
must anticipate a delayed response from
A
Resilient Tunnel
San Francisco LAN
VSU
Router
HUB
VSU
Router
Figure 68
illustrates
Primary
End-point
VSU
Router
B
HUB
LAN
VSU
Router
C
Secondary
End-point
then begins to establish
A
Issue 4 May 2005
LAN
213
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