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

 

 

 

 

 

 

 

Link down

 

 

 

 

 

 

#2

 

 

 

 

Device

 

 

 

 

 

 

 

 

 

 

 

 

 

 

unreachable

 

P2

P3

Link down

 

 

 

 

 

 

 

#2

 

CE1

PE1

P1

 

P6

PE2

 

 

 

Link down

 

 

 

 

 

 

#1

MPLS

 

 

 

 

 

 

 

 

 

 

 

 

 

P4 Black hole

P5

 

 

 

 

MNG core

 

 

MNG core

182431

 

 

 

 

 

 

 

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.

 

 

Cisco Active Network Abstraction Fault Management User Guide, Version 3.6 Service Pack 1

 

 

 

 

 

 

OL-14284-01

 

 

4-13

 

 

 

 

 

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Cisco Systems 3.6 specifications Generic Routing Encapsulation GRE Tunnel Down/Up, GRE Tunnel Down/Up Alarm

3.6 specifications

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