The show ip ospf interface Command

show ip ospf interface [type-number]

This command is used to show how OSPF has been configured on an interface level, as well as how it is working at the interface. This level of detail is excellent for troubleshooting configuration errors.

Example 5-8 shows the output of this command. Table 5-10 explains how to read this information.

Example 5-8 show ip ospf interface [type-number] Output

SanJose#show ip ospf interface fastethernet1/0

FastEthernet1/0 is up, line protocol is up Internet Address 140.100.17.129/28, Area 3

Process ID 100, Router ID 140.100.32.10, Network Type BROADCAST, Cost: 1 Transmit Delay is 1 sec, State DR, Priority 100

Designated Router (ID) 140.100.32.10, Interface address 140.100.17.129 Backup Designated router (ID) 140.100.23.1, Interface address 140.100.17.130 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:06 Neighbor Count is 3, Adjacent neighbor count is 2 Adjacent with neighbor 140.100.17.132 Adjacent with neighbor 140.100.17.131

Adjacent with neighbor 140.100.23.1 (Backup Designated Router) Suppress hello for 0 neighbor(s)

Table 5-10 Explanation of the show ip ospf interface Command

Field

Explanation

FastEthernet1/0 is up, line protocol

This should be seen as two statements. The first half of the

is up

sentence indicates that the physical line is operational. This

meaning differs with the type of interface; for Ethernet, it

indicates the presence of the transceiver. The second portion

of the sentence indicates that the data link layer is working.

Internet Address 140.100.17.129/28,

The IP address and mask configured on the interface.

Area 3

Area 3

The OSPF area for which the interface is configured.

Process ID 100, Router ID

The autonomous system number, which is in fact the OSPF

140.100.32.10

process ID.

The router ID that will be advertised in the LSA updates.

Network Type BROADCAST

The type of network that the interface is connected to, which

indicates how neighbors are found and adjacencies are

formed.

Cost: 1

The metric cost of the link, which, although not stated, was

probably dynamically chosen using the Cisco defaults.

Transmit Delay is 1 sec

The anticipated time taken to send an update to the neighbor.

The default is 1 second.

State DR

The state of the link in reference to establishing adjacencies.

This field is extremely useful in troubleshooting. Here are the

states in order:

DOWN—Heard from no one.

ATTEMPT—Sent a hello on an NBMA, but haven't heard

back.

INIT—Heard a hello, but have not achieved neighbor status.

TWO-WAY—Established full neighbor relationship; saw itself in the neighbor's hello table.

EXSTART—Starting up the link for exchanging DDPs.

EXCHANGE—Sending DDPs to other router.

LOADING—Building the database and LSAs from the DDPs.

FULL—Established adjacency. DR—Is the designated router for this LAN.

continues

Table 5-10 Explanation of the show ip ospf interface Command (Continued)

Field

Explanation

Priority 100

The priority is sent in the Hello protocol and is used to

determine the election of the designated router and the

backup designated router. The value of 1 means that the

router is prepared to be elected. If every other router has the

priority of 1, the highest router ID will select the routers.

Designated Router (ID)

The address of the elected designated router. Note that the ID

140.100.32.10, Interface address

and the interface ID differ. This is a useful field for

140.100.17.129

troubleshooting misconfiguration.

Backup Designated router (ID)

The address of the backup designated router. Note that both

140.100.23.1, Interface address

the ID and the interface are given, and they differ.

140.100.17.130

Timer intervals configured, Hello 10,

It is possible to change these timers and sometimes necessary

Dead 40, Wait 40, Retransmit 5

if connecting to another vendor's equipment that has

different defaults. These timers should be consistent

throughout the area. The defaults are as follows:

Hello: 10

Dead: 40

Wait: 40

Retransmit: 5

Hello due in 00:00:06

When the next hello packet is due to be sent out of the

interface.

Neighbor Count is 3, Adjacent

The number of routers that have neighbor relationships.

neighbor count is 2

Note that the number of routers with which adjacency is

established is less than the number of neighbors. This is

because there is a designated router and a backup designated

router, whose responsibility it is to maintain the adjacencies

with all routers on the LAN.

Adjacent with neighbor 140.100.23.1 The router ID of the adjacent router, which is the backup (Backup Designated Router) designated router in this case.

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