Troubleshooting OSPF Routing Tables CCSP Course Center in Gurgaon India

Network Bulls
www.networkbulls.com
Best Institute for CCNA CCNP CCSP CCIP CCIE Training in India
M-44, Old Dlf, Sector-14 Gurgaon, Haryana, India
Call: +91-9654672192


Figure 4-10 Troubleshooting OSPF Routing Tables
An OSPF route found in the routing table can have a variety of different codes:
■ O: OSPF intra-area, within the same area, route from a router within the same OSPF area
■ O IA: OSPF inter-area, from another area in the OSPF network, route from a router in a
different OSPF area
■ O E1 or E2: An external OSPF route from another autonomous system
If you have a single OSPF area, you should not see O IA routes in the routing table. Example 4-17
has both an O IA and an O E2 route.
Example 4-17 Determining OSPF Route Types
RouterX#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
ia - IS-IS inter area, * - candidate default,
o - ODR, P - periodic downloaded static route
Troubleshoot
OSPF Neighbor
Adjacencies
Troubleshoot
OSPF Routing
Table Issues
Troubleshoot
OSPF
Authentication
Are all
required OSPF
networks being
advertised?
Are there
any route filters
that block OSPF
networks?
Troubleshooting OSPF 165
The network command that you configure under the OSPF routing process also indicates which
networks OSPF advertises.
The show ip protocols command indicates whether any route filters have been implemented,
which can affect which routes are seen in the routing table. The command, as shown in Example
4-18, also displays the networks that have been configured to be advertised to other OSPF routers.
Troubleshooting Plaintext Password Authentication
If you are using OSPF password authentication, you must also be prepared to troubleshoot any
authentication problems that may occur during the adjacency process.
Gateway of last resort is not set
172.16.0.0/32 is subnetted, 1 subnets
O 172.16.31.100 [110/1563] via 10.140.1.1, 00:03:15, Serial0/0/0
10.0.0.0/24 is subnetted, 5 subnets
C 10.2.2.0 is directly connected, FastEthernet0/0
O IA 10.1.1.0 [110/1563] via 10.140.1.1, 00:03:15, Serial0/0/0
O 10.140.2.0 [110/3124] via 10.140.1.1, 00:03:15, Serial0/0/0
[110/3124] via 10.23.23.2, 00:03:15, Serial0/0/1
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.64/28 is directly connected, Loopback0
E2 192.168.1.81/32 [110/1563] via 10.23.23.2, 00:03:17, Serial0/0/1
Example 4-18 Determining Whether Route Filters Have Been Implemented
RouterX#show ip protocols
Routing Protocol is "ospf 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 192.168.1.65
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
10.2.2.3 0.0.0.0 area 0
10.23.23.1 0.0.0.0 area 0
10.140.1.2 0.0.0.0 area 0
192.168.1.65 0.0.0.0 area 0
Reference bandwidth unit is 100 mbps
Routing Information Sources:
Gateway Distance Last Update
192.168.1.81 110 00:04:52
172.16.31.100 110 00:04:52
Distance: (default is 110)
Example 4-17 Determining OSPF Route Types (Continued)
166 Chapter 4: Single-Area OSPF Implementation
You can use the debug ip ospf adj command to display OSPF adjacency-related events. This
command is useful when troubleshooting authentication.
If plaintext password authentication is configured on the Router X serial 0/0/1 interface but no
authentication is configured on the Router Y serial 0/0/1 interface, the routers will not be able to
form an adjacency over that link. The output of the debug ip ospf adj command shown in
Example 4-19 illustrates that the routers report a mismatch in authentication type; no OSPF
packets will be sent between the neighbors.
If plaintext password authentication is configured on the Router X serial 0/0/1 interface and on the
router Y serial 0/0/1 interface, but the interfaces are configured with different passwords, the
routers will not be able to form an adjacency over that link.
The output of the debug ip ospf adj command shown in Example 4-20 illustrates that the routers
report a mismatch in authentication key; no OSPF packets will be sent between the neighbors.
Example 4-19 Determining Whether an Authentication Mismatch Exists
RouterX#debug ip ospf adj
*Feb 17 18:51:31.242: OSPF: Rcv pkt from 192.168.1.102, Serial0/0/1 :
Mismatch Authentication type. Input packet specified type 0, we use type 1
RouterY#debug ip ospf adj
*Feb 17 18:50:43.046: OSPF: Rcv pkt from 192.168.1.101, Serial0/0/1 :
Mismatch Authentication type. Input packet specified type 1, we use type 0
NOTE The different types of authentication have these codes:
■ Null is type 0
■ Simple password is type 1
■ MD5 is type 2
Example 4-20 debug ip ospf adj Command Output Confirms an Authentication Mismatch
RouterX#debug ip osp adj
*Feb 17 18:54:01.238: OSPF: Rcv pkt from 192.168.1.102, Serial0/0/1 :
Mismatch Authentication Key - Clear Text
RouterY#debug ip ospf adj
*Feb 17 18:53:13.050: OSPF: Rcv pkt from 192.168.1.101, Serial0/0/1 :
Mismatch Authentication Key - Clear Text
Review Questions 167
Summary of Troubleshooting OSPF
Troubleshooting OSPF is an important skill. Most OSPF problems are related to configuration and
will most likely show themselves when the routers attempt to form OSPF adjacencies.
The following summarizes the key points that were discussed in this section:
■ Troubleshooting OSPF involves looking at neighbor adjacencies, routing tables, and
authentication issues.
■ Use the show ip interface command to verify the MTU of an OSPF interface.
■ Use the show ip ospf interface command to help troubleshoot whether OSPF is enabled on
an interface.
■ Use the debug ip ospf adj command to troubleshoot OSPF authentication.