Monitoring Troubleshooting an OSPF Network | OSPF Network Design Solutions

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Table 8-14 describes some fields that are useful in a troubleshooting environment.

**Table 8-14** `show ip ospf neighbor detail` output definition
Field	Description

Neighbor x.x.x.x	Neighbor router ID
interface address x.x.x.x	IP address of the interface
In the area	Area and interface through which OSPF neighbor is known
Neighbor priority	Router priority of neighbor, neighbor state
State	OSPF state
Options	Hello packet options field contents (E-bit only; possible values are 0 and 2; 2 indicates area is not a stub; 0 indicates area is a stub)
Dead timer	Expected time before Cisco IOS software will declare neighbor dead

show ip ospf virtual-links Command

To display parameters about and the current state of OSPF virtual links, use the show ip ospf virtual-links EXEC command. This command provides you with detailed information regarding OSPF virtual links. The actual information output from the command is defined in the example that follows.

Usage Guidelines: The information displayed by show ip ospf virtual-links is useful in debugging OSPF routing operations.

Example:

    OSPF_Router# show ip ospf virtual-links    Virtual Link to router 160.89.101.2 is up    Transit area 0.0.0.1, via interface Ethernet0, Cost of using 10    Transmit Delay is 1 sec, State POINT_TO_POINT    Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5    Hello due in 0:00:08    Adjacency State FULL

Table 8-15 describes some fields that are useful in a troubleshooting environment.

**Table 8-15** `show ip OSPF virtual-links` output definition
Field	Description

Virtual Link to router 160.89.101.2 is Up	Specifies the OSPF neighbor, and if the link to that neighbor is Up or Down
Transit area 0.0.0.1	The transit area through which the virtual link is formed
via interface Ethernet0	The interface through which the virtual link is formed
Cost of using 10	The cost of reaching the OSPF neighbor through the virtual link
Transmit Delay is 1 sec	The transmit delay on the virtual link
State POINT_TO_POINT	The state of the OSPF neighbor
Timer intervals...	The various timer intervals configured for the link
Hello due in 0:00:08	When the next hello is expected from the neighbor
Adjacency State FULL	The adjacency state between the neighbor

show ip ospf summary-address Command

Example syntax for the show ip ospf summary-address command is as follows:

    AST7401#sho ip ospf summary-address    OSPF Process 5774, Summary-address

Troubleshooting OSPF

This section deals with the inevitable network routing problems. These problems can take many forms, from straightforward loss of connectivity to the more complex routing loops. Even though additional problems exist, such as access list configuration, buffer usage, and queue sizes, they are beyond the scope of this book. The reader is referred to CCO (http://www.cisco.com) for information regarding these subjects.

This section provides a variety of resources that can assist in resolving these issues and briefly mentions other issues that are not within the scope of this book.

As with any potentially complex problem, certain techniques or methodology have evolved to deal with troubleshooting network-related problems. This troubleshooting methodology is not only applicable to OSPF, it can also be used to assist you with any network problem.

As this book deals primarily with OSPF, a routing protocol, take a minute to review how and what the routing process uses for sources of input on a larger scale (that is, not just OSPF LSAs). This information will greatly assist you as routing problems can be many layered or give you false indications. For purposes of the discussion here, consider how Cisco routers build their IP routing tables. Figure 8-2 illustrates an example of the many types of inputs into the routing process that are discussed.

Figure 8-2 Static and dynamic inputs to routing.

Proper routing will be achieved based upon the following sources of information gained from the network:

• Dynamic routing protocols and their associated metrics (cost)

• Redistribution between routing protocols

• Static routes which might differ from dynamic routes

• Policy decisions implemented via access lists

• ARP and Inverse ARP

• Local interface configuration

• Local interface status via counters, timers, and carrier detection

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