Cisco Systems network hardware 3.6 Manual

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Cisco Systems network hardware 3.6
4-13
Cisco Active Network Abstraction Fault Management User Guide, Version 3.6 Service Pack 1
OL-14284-01
Chapter 4 Advanced Correlation Scenarios
Generic Routing Encapsulation (GRE) Tunnel Down/Up
Multi Route Correlation Example 4
In this example, two paths exists from CE1 to PE2. Several links went down, and there is a MPLS black
hole in the multi route segment. As a result router CE1 became unreachable.
Figure 4-13 Multi Route Correlation Example 4
In this case the system will provide the following report:
• Root cause—Device Unreachable. Link Down #2 is identified as the root cause for Device
Unreachable (CE1).
Generic Routing Encapsulation (GRE) Tunnel Down/Up
Generic Routing Encapsulation (GRE) is a tunneling protocol that encapsulates a variety of network
layer packets inside IP tunneling packets, creating a virtual point-to-point link to devices at remote
points over an IP network. It is used on the Internet to secure virtual private networks (VPNs). GRE
encapsulates the entire original packet with a standard IP header and GRE header before the IPsec
process. GRE can carry multicast and broadcast traffic, making it possible to configure a routing
protocol for virtual GRE tunnels. The routing protocol detects loss of connectivity and reroutes packets
to the backup GRE tunnel, thus providing high resiliency.
GRE is stateless, which means that the tunnel endpoints do not monitor the state or availability of other
tunnel endpoints. This feature helps service providers support IP tunnels for clients, who don't know the
service provider's internal tunneling architecture. It gives clients the flexibility of reconfiguring their IP
architectures without worrying about connectivity.
GRE Tunnel Down/Up Alarm
When a GRE tunnel link exists, if the status of the IP interface of the GRE tunnel edge changes to down,
a GRE Tunnel Down alarm is created. The IP Interface Down alarms of both sides of the link will
correlate to the GRE Tunnel Down alarm. The GRE Tunnel Down alarm will initiate an IP based flow
toward the GRE destination. If an alarm is found during the flow, it will correlate to it.
Device
unreachable
CE1 PE1 P1
P4
P2 P3
P5
P6 PE2
Link down
#1
Link down
#2
Link down
#2
MPLS
Black hole
MNG core MNG core
182431
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