Cisco Cisco 1700 2600 3600 3700 Series VPN Module 백서
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Note that by configuring these commands, static routes are automatically added for the remote addresses and are
installed in the Routing Information Base (RIB) only if a dual-active scenario occurs. As a result, no packets are
forwarded between the switches through the heartbeat interfaces until the VSL is brought down.
When the VSL does go down, a unique internal MAC address (selected from the pool of MAC addresses reserved
for the line card) is assigned for each of the local interfaces, and sending BFD heartbeat packets brings up BFD
neighbors. If the standby virtual switch has taken over as active, a BFD “adjacency-up” event is generated,
neighbors. If the standby virtual switch has taken over as active, a BFD “adjacency-up” event is generated,
indicating that a dual-active situation has occurred.
Fast Hello Detection
With 12.2(33)SXI, a Fast Hello detection mechanism was introduced. This is similar to IP-BFD, as it is a dedicated
direct link heartbeat between the VSS switches. However, Fast Hello is a L2 connection and you can configure up
to 4 non-VSL links. The two chassis will periodically exchange Fast Hello heartbeat packets that contain the switch
state. When the VSL fails, the Fast Hello packets are no longer received on each switch, thus indicating that a
dual-active scenario has occurred (Figure 28).
Figure 28. Dual-Active Detection Using Fast Hello
In order for Fast Hello to operate, the interfaces must be enabled with this protocol. Unlike IP-BFD, that only
exchanges hello packets after the VSL fails, Fast Hello exchanges heartbeat messages throughout the period that
the VSL remains up, thereby reducing the time it takes to detect the dual-active scenario.
vss(config)# interface fastethernet 1/2/40
vss(config-if)# dual-active fast hello
WARNING: Interface FastEthernet1/2/40 placed in restricted config mode. All
extraneous configs removed!
extraneous configs removed!
Up to four interfaces (directly connected) on each chassis can be configured. These interfaces must be physical
interfaces, no logical ports (for example, SVI).
vss(config-if)# no shutdown
vss(config-if)# exit
vss(config)# exit
vss# show run interface fastethernet 1/2/40
interface FastEthernet1/2/40
no switchport
no ip address