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neighbor goes
down.
OSPF link-state database This data structure contains topology information for all
areas in which a router participates, in addition to information
about how to route traffic to networks residing in
other areas or autonomous systems.
OSPF Routing Information Base The OSPF Routing Information Base (RIB) stores the results
of the OSPF shortest path first (SPF) calculations.
Foundation Topics
OSPF Troubleshooting
Chapter 6, “Introduction to Troubleshooting Routing Protocols,” began with a discussion
on troubleshooting routing protocols from a generic perspective. Chapter 6 also reviewed
router and Cisco Express Forwarding (CEF) data structures, as well as Enhanced Interior
Gateway Routing Protocol (EIGRP), including EIGRP data structures. Finally, the chapter
concluded with coverage of a collection of commands for gathering information from
EIGRP data structures.
This section addresses the OSPF routing protocol in a similar fashion to the Chapter 6
treatment of EIGRP. Specifically, this section examines OSPF data structures, reviews
OSPF operation, and presents you with commands useful for collecting information from
the OSPF data structures.
OSPF is a nonproprietary link-state protocol. Like EIGRP, OSPF offers fast convergence
and is a popular enterprise routing protocol.
OSPF Data Structures
Whereas EIGRP has three major data structures (that is, EIGRP interface table, EIGRP
neighbor table, and EIGRP topology table), OSPF uses four data structures, as described
in Table 7-2.
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Chapter 7: OSPF and Route Redistribution Troubleshooting 171
Of the data structures listed in Table 7-2, the OSPF link-state database contains the most
comprehensive collection of information. Therefore, the OSPF link-state database is valuable
to view for OSPF troubleshooting.
An OSPF link-state database stored in an OSPF router contains comprehensive information
about the topology within a specific OSPF area. Note that if a router is participating
in more than one OSPF area, the router contains more than one OSPF link-state database
(one for each area). Because an OSPF link-state database contains the topology of an
OSPF area, all routers participating in that OSPF area should have identical OSPF linkstate
databases.
In addition to networks residing in OSPF areas, an OSPF router can store information
about routes redistributed into OSPF in an OSPF link-state database. Information about
these redistributed routes is stored in an area separate from the area-specific OSPF linkstate
databases.
OSPF Operation
Because OSPF is a link-state protocol, it receives LSAs from adjacent OSPF routers. The
Dijkstra SPF algorithm takes the information contained in the LSAs to determine the
shortest path to any destination within an area of the network.
Although multiple routers can participate in a single OSPF area, larger OSPF networks are
often divided into multiple areas. In a multiarea OSPF network, a backbone area (numbered
area 0) must exist, and all other areas must connect to area 0. If an area is not physically
adjacent to area 0, a virtual link can be configured to logically connect the
nonadjacent area with area 0.
OSPF Metric
OSPF uses a metric of cost, which is a function of bandwidth. Cost can be calculated as
follows:
cost = 100,000,000 / bandwidth (in kbps)
Designated Router
A multiaccess network can have multiple routers residing on a common network segment.
Rather than having all routers form a full mesh of adjacencies with one another, a
designated router (DR) can be elected, and all other routers on the segment can form an
adjacency with the DR, as illustrated in Figure 7-1.
A DR is elected based on router priority, with larger priority values being more preferable.
If routers have equal priorities, the DR is elected based on the highest OSPF router ID. An
OSPF router ID is determined by the IP address of the loopback interface of the router or
by the highest IP address on an active interface, or it can be statically defined if the router
is not configured with a loopback interface.
A backup designated router (BDR) is also elected. Routers on the multiaccess network
also form adjacencies if the DR becomes unavailable.
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Designated Router
(DR)
Adjacency
R1 R2
R4
Adjacency
R3
Adjacency Adjacency
Figure 7-1 Designated Router Adjacencies
Key
Topic
OSPF Router Types
When an OSPF network grows beyond a single area, you need to be aware of the role
played by each OSPF router in a topology. Specifically, four OSPF router types exist:
■ Internal router: All the networks directly connected to an internal router belong to
the same OSPF area. Therefore, an internal router has a single link-state database.
■ Area border router (ABR): An ABR connects to more than one OSPF area and
therefore maintains multiple link-state databases (one for each connected area). A primary
responsibility of an ABR is to exchange topological information between the
backbone area and other connected areas.
■ Backbone router: A backbone router has at least one of its connected networks participating
in OSPF area 0 (that is, the backbone area). If all the connected networks
are participating in the backbone area, the router is also considered to be an internal
router. However, if a backbone router has one or more connected networks participating
in another area, the backbone router is also considered to be an ABR.
■ Autonomous system boundary router (ASBR): An ASBR has at least one connected
route participating in an OSPF area and at least one connected route participating
in a different autonomous system. The primary role of an ASBR is to exchange
information between an OSPF autonomous system and one or more external autonomous
systems.
As an example, Figure 7-2 illustrates these various OSPF router types.
Table 7-3 lists the OSPF router type or types for each OSPF router in the topology (that is,
routers R1, R2, R3, and R4).
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Table 7-3 OSPF Router Types in Figure 7-2
Router OSPF Router Type(s)
R1 Internal (because all the connected routes of the router belong to the same OSPF
area)
R2 ABR (because the connected routes of the router belong to more than one OSPF
area)
Backbone (because the router has at least one connected route participating in
OSPF area 0)
R3 Internal (because all the connected routes of the router belong to the same OSPF
area)
Backbone (because the router has at least one connected route participating in
OSPF area 0)
R4 Backbone (because the router has at least one connected route participating in
OSPF area 0)
ASBR (because the router has at least one connected route participating in an OSPF
area and one connected route participating in a different autonomous system)
OSPF
Area 1
OSPF
Area 0
EIGRP
AS 100
SW2
R1 SW1 R2
SW3
R3
R4
R5
Figure 7-2 OSPF Router Types
Key
Topic
Chapter 7: OSPF and Route Redistribution Troubleshooting 173
OSPF LSA Types
As previously mentioned, an OSPF router receives LSAs from adjacent OSPF neighbors.
However, OSPF uses multiple LSA types. Table 7-4 lists the common LSA types you
might encounter when troubleshooting a Cisco-based OSPF network.
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To illustrate how the database of an OSPF router is populated with these various LSA
types, once again consider Figure 7-2. Table 7-5 shows the number of each LSA type
present in the OSPF routers of the topology. Note that the topology has no Type 7 LSAs
because it does not contain NSSAs.
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Table 7-4 LSA Types
LSA Type Description
1 All OSPF routers source Type 1 LSAs. These advertisements list information
about directly connected subnets, the OSPF connection types of a router, and
the known OSPF adjacencies of a router. A Type 1 LSA is not sent out of its
local area.
2 The designated router on a multiaccess network sends a Type 2 LSA for that network
if the network contains at least two routers. A Type 2 LSA contains a listing
of routers connected to the multiaccess network and, like a Type 1 LSA, is
constrained to its local area.
3 A Type 3 LSA is sourced by an ABR. Each Type 3 LSA sent into an area contains
information about a network reachable in a different area. Note that network information
is exchanged only between the backbone area and a nonbackbone
area, as opposed to being exchanged between two nonbackbone areas.
4 Similar to a Type 3 LSA, a Type 4 LSA is sourced by an ABR. However, instead
of containing information about OSPF networks, a Type 4 LSA contains information
stating how to reach an ASBR.
5 A Type 5 LSA is sourced by an ASBR and contains information about networks
reachable outside the ospf domain. A Type 5 LSA is sent to all OSPF areas, except
for stub areas. Note: The ABR for a stub area sends default route information
into the stub area, rather than the network-specific Type 5 LSAs.
7 A Type 7 LSA is sourced from a router within a not-so-stubby-area (NSSA).
Whereas a stub area does not connect to an external autonomous system, an
NSSA can. Those external routes are announced by an ABR of the NSSA using
Type 7 LSAs. Like a stub area, however, external routes known to another OSPF
area are not forwarded into an NSSA.
Key
Topic
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Key
Topic
Table 7-5 OSPF LSA Types in Figure 7-2
Router Type 1 LSAs Type 2 LSAs Type 3 LSAs Type 4 LSAs Type 5 LSAs
R1 2 (because
two routers
are in area 1)
1 (because only
one of the multiaccess
networks
of area 1
contains at least
two routers)
3 (because the
area 1 database
contains
the three networks
in area 0)
1 (because the
topology contains
only one
ASBR)
2 (because the
EIGRP AS contains
two networks that
are external to the
OSPF AS)
R2 5 (because
area 1 has two
routers and
area 0 has
three routers)
1 (because area
1 contains only
one multiaccess
network containing
at least
two routers,
while area 0
contains zero
multiaccess networks
with at
least two
routers)
5 (because the
area 1 database
contains
the three networks
in area
0, and the area
0 database
contains the
two networks
in area 1)
1 (because the
topology contains
only one
ASBR)
2 (because the
EIGRP AS contains
two networks that
are external to the
OSPF AS)
R3 3 (because
area 0 has
three routers)
0 (because area
0 does not contain
any multiaccess
networks
with at least two
routers)
2 (because the
area 0 database
contains
the two networks
in area 1)
1 (because the
topology contains
only one
ASBR)
2 (because the
EIGRP AS contains
two networks that
are external to the
OSPF AS)
R4 3 (because
area 0 has
three routers)
0 (because area
0 does not contain
multiaccess
networks with
at least two
routers)
2 (because the
area 0 database
contains
the two networks
in area 1)
1 (because the
topology contains
only one
ASBR)
2 (because the
EIGRP AS contains
two networks that
are external to the
OSPF AS)
Chapter 7: OSPF and Route Redistribution Troubleshooting 175
OSPF Network Types
OSPF can support multiple network types. For example, a multiaccess network such as
Ethernet is considered to be an OSPF broadcast network. Table 7-6 shows a listing of supported
OSPF network types and characteristics of each.
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Forming an OSPF Adjacency
Although two OSPF routers can form an adjacency (that is, become neighbors) through
the exchange of Hello packets, the following parameters in the Hello packets must match:
■ Hello timer: This timer defaults to 10 seconds for broadcast and point-to-point network
types. The default is 30 seconds for nonbroadcast and point-to-multipoint network
types.
■ Dead timer: This timer defaults to 40 seconds for broadcast and point-to-point network
types. The default is 120 seconds for nonbroadcast and point-to-multipoint network
types.
■ Area number: Both ends of a link must be in the same OSPF area.
■ Area type: In addition to a normal OSPF area type, an area type could be either stub
or NSSA.
■ Subnet: Note that this common subnet is not verified on point-to-point OSPF
networks.
■ Authentication information: If one OSPF interface is configured for authentication,
the OSPF interface at the other end of the link should be configured with matching
authentication information (for example, authentication type and password).
Adjacencies are not established upon the immediate receipt of Hello messages. Rather, an
adjacency transitions through multiple states, as described in Table 7-7.
Key
Topic
Key
Topic
Table 7-6 OSPF Network Types and Characteristics
Broadcast Nonbroadcast Point-to-
Point
Point-to-
Multipoint
Characteristics Default OSPF
network type on
LAN interfaces
Default OSPF network
type on Frame Relay
serial interfaces
Default OSPF
network type
on non-Frame
Relay serial interfaces
Can be configured
on
any interface
Neighbors automatically
discovered
Neighbors statically
configured
Routers at
each end of a
link form adjacencies
Neighbors
automatically
determined
All routers on
same subnet
All routers on same
subnet
Each point-topoint
link on a
separate subnet
All routers on
same subnet
Has a designated
router
Has a designated router Does not have
a designated
router
Does not
have a designated
router
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Chapter 7: OSPF and Route Redistribution Troubleshooting 177
Key
Topic
Tracking OSPF Advertisements Through a Network
When troubleshooting an OSPF issue, tracking the path of OSPF advertisements can be
valuable in determining why certain entries are in a router’s RIB.
As an example, notice network 192.168.1.0/24 in the topology provided in Figure 7-3, and
consider how this network is entered into the RIB of the other OSPF routers.
Table 7-7 Adjacency States
State Description
Down This state indicates that no Hellos have been received from a neighbor.
Attempt This state occurs after a router sends a unicast Hello (as opposed to a multicast
Hello) to a configured neighbor and has not yet received a Hello from that neighbor.
Init This state occurs on a router that has received a Hello message from its neighbor;
however, the OSPF router ID of the receiving router was not contained in the
Hello message. If a router remains in this state for a long period, something is
probably preventing that router from correctly receiving Hello packets from the
neighboring router.
2-Way This state occurs when two OSPF routers have received Hello messages from each
other, and each router saw its own OSPF router ID in the Hello message it received.
The 2-Way state could be a final state for a multiaccess network if the network
has already elected a designated router and a backup designated router.
ExStart This state occurs when the designated and nondesignated routers of a multiaccess
network begin to exchange information with other routers in the multiaccess network.
If a router remains in this state for a long period, a maximum transmission
unit (MTU) mismatch could exist between the neighboring routers, or a duplicate
OSPF router ID might exist.
Exchange This state occurs when the two routers forming an adjacency send one another
database descriptor (DBD) packets containing information about a router’s linkstate
database. Each router compares the DBD packets received from the other
router to identify missing entries in its own link-state database. Like the ExStart
state, if a router remains in the Exchange state for a long period, the issue could
be an MTU mismatch or a duplicate OSPF router ID.
Loading Based on the missing link-state database entries identified in the Exchange state,
the Loading state occurs when each neighboring router requests the other router
to send those missing entries. If a router remains in this state for a long period, a
packet might have been corrupted, or a router might have a memory corruption issue.
Alternatively, it is possible that such a condition could result from the neighboring
routers having an MTU mismatch.
Full This state indicates that the neighboring OSPF routers have successfully exchanged
their link-state information with one another, and an adjacency has been
formed.
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The following steps describe how network 192.168.1.0/24, which is directly connected to
router R1, is learned by the RIB of routers R2, R3, and R4.
Step 1. Router R1 creates an LSA for the 192.168.1.0/24 network in the area 1 linkstate
database.
Step 2. Router R2, which also has a copy of the area 1 link-state database, runs the
SPF algorithm to determine the best path through area 1 to reach the
192.168.1.0/24 network. The result is stored in router R2’s RIB.
Step 3. Router R2 informs area 0 routers about this network by injecting a Type 3 LSA
into the link-state database of area 0. This LSA includes the cost to reach the
192.168.1.0/24 network, from the perspective of router R2.
Step 4. Each of the other area 0 routers (that is, routers R3 and R4) run the SPF algorithm
to determine the cost to reach router R2. This cost is then added to the
cost router R2 advertised in its Type 3 LSA, and the result is stored in the RIB
for routers R3 and R4.
OSPF Troubleshooting Commands
With an understanding of OSPF’s data structures and an understanding of OSPF’s router
types, network types, LSA types, and adjacency states, you can now strategically use
Cisco IOS show and debug commands to collect information about specific steps in the
routing process. Table 7-8 shows a collection of such commands, along with their descriptions,
and the step of the routing process or OSPF data structure each command can be
used to investigate.
Area 1 Link-State Database Area 0 Link-State Database
Type 1 LSA RIB SW2
SPF Type 3
LSA
192.168.1.0/24
SW1 R3
OSPF
Area 0
RIB
OSPF
Area 1 SPF
SPF
EIGRP
AS 100
SW3
R1 R2 R4
SW3 R5
SW2
SW1
RIB
Figure 7-3 Tracking an OSPF Advertisement
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Chapter 7: OSPF and Route Redistribution Troubleshooting 179
Key
Topic
Table 7-8 OSPF Troubleshooting Commands
Command Routing Component
or Data Structure
Description
show ip ospf interface [brief] OSPF interface table This command displays all of a
router’s interfaces configured to participate
in an OSPF routing process.
The brief option provides a more
concise view of OSPF interface
information.
show ip ospf neighbor OSPF neighbor table This command displays the state of
OSPF neighbors learned off a
router’s active OSPF interfaces.
show ip ospf database OSPF link-state database
This command displays the LSA
headers contained in a router’s OSPF
link-state database.
show ip ospf statistics OSPF RIB This command provides information
about how frequently a router is executing
the SFP algorithm. Additionally,
this command shows when the
SPF algorithm last ran.
debug ip ospf monitor OSPF RIB This command provides real-time
updates showing when a router’s SPF
algorithm is scheduled to run.
debug ip routing IP routing table This command displays updates that
occur in a router’s IP routing table.
Therefore, this command is not specific
to OSPF.
show ip route ospf IP routing table This command shows routes known
to a router’s IP routing table that
were learned via OSPF.
debug ip ospf packet Exchanging OSPF information
with neighbors
This command shows the transmission
and reception of OSPF packets
in real time. This command is useful
for monitoring Hello messages.
debug ip ospf adj Exchanging OSPF information
with neighbors
This command provides real-time
updates about the formation of an
OSPF adjacency.
continues
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Example 7-1 provides sample output from the show ip ospf interface brief command. Notice
that the output shows summary information about all the router interfaces participating
in an OSPF routing process, including the OSPF process ID (PID), the OSPF area, and
the network associated with each interface. Additionally, the output contains the OSPF
metric of cost, information about the state of an interface, and the number of neighbors
that an interface has.
Example 7-1 show ip ospf interface brief Command Output
R2# show ip ospf interface brief
Interface PID Area IP Address/Mask Cost State Nbrs F/C
Lo0 1 0 10.2.2.2/32 1 LOOP 0/0
Se1/0.2 1 0 172.16.2.1/30 64 P2P 1/1
Se1/0.1 1 0 172.16.1.2/30 64 P2P 1/1
Fa0/0 1 0 192.168.0.22/24 10 DR 1/1
Example 7-2 provides sample output from the show ip ospf neighbor command. A neighbor’s
OSPF router ID is shown. For a multiaccess segment (FastEthernet 0/0 in this example),
the neighbor’s priority, used for designated router election, is shown. The remaining
dead time for a neighbor is displayed. Finally, the output contains information about each
neighbor’s interface (and the IP address of that interface) through which the neighbor is
reachable.
Table 7-8 OSPF Troubleshooting Commands
Command Routing Component
or Data Structure
Description
debug ip ospf events Exchanging OSPF information
with neighbors
This command shows real-time information
about OSPF events, including
the transmission and
reception of Hello messages and
LSAs. This command might be useful
on a router that appears to be ignoring
Hello messages received from
a neighboring router.
show ip ospf virtual-links OSPF interface table This command provides information
about the status of OSPF virtual
links that are required for areas not
physically adjacent to the backbone
area (that is, area 0).
(Continued)
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Chapter 7: OSPF and Route Redistribution Troubleshooting 181
Example 7-2 show ip ospf neighbor Command Output
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.4.4.4 0 FULL/ - 00:00:38 172.16.2.2 Serial1/0.2
10.3.3.3 0 FULL/ - 00:00:38 172.16.1.1 Serial1/0.1
10.1.1.1 1 FULL/BDR 00:00:36 192.168.0.11 FastEthernet0/0
Example 7-3 provides sample output from the show ip ospf database command. The
database of the router has been populated with various LSAs, as previously discussed.
The Router Link States in the database come from Type 1 LSAs, whereas the Net Link
States come from Type 2 LSAs.
Example 7-3 show ip ospf database Command Output
R2# show ip ospf database
OSPF Router with ID (10.2.2.2) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
10.1.1.1 10.1.1.1 969 0x8000000C 0x0092ED 3
10.2.2.2 10.2.2.2 968 0x80000013 0x00FD7D 6
10.3.3.3 10.3.3.3 1598 0x80000007 0x00DAEA 6
10.4.4.4 10.4.4.4 1597 0x80000007 0x0009B1 6
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.1.2.2 10.4.4.4 1622 0x80000001 0x00CE1D
192.168.0.22 10.2.2.2 968 0x8000000B 0x008AF8
Example 7-4 provides sample output from the show ip ospf statistics command. Notice
that the primary focus of the command is on the SPF algorithm. For example, you can see
from the output how many times the SPF algorithm has been executed for a particular
OSPF area.
Example 7-4 show ip ospf statistics Command Output
R2# show ip ospf statistics
OSPF Router with ID (10.2.2.2) (Process ID 1)
Area 0: SPF algorithm executed 23 times
Summary OSPF SPF statistic
SPF calculation time
Delta T Intra D-Intra Summ D-Summ Ext D-Ext Total Reason
00:21:00 12 0 0 0 0 0 16 R, N,
00:20:50 16 0 0 0 0 0 20 R,
00:19:40 12 4 0 0 0 0 20 R, N,
00:19:30 12 0 0 0 0 0 16 R, N,
00:19:20 16 0 0 0 4 0 24 R,
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00:18:09 12 4 0 0 0 0 16 R, N,
00:17:59 12 0 0 0 0 0 16 R, N,
00:17:49 16 0 0 0 0 0 20 N,
00:16:37 4 4 0 0 0 0 8 R, N,
00:16:27 16 0 0 0 0 0 20 R, N,
RIB manipulation time during SPF (in msec):
Delta T RIB Update RIB Delete
00:21:00 3 0
00:20:52 4 0
00:19:42 0 3
00:19:32 3 0
00:19:22 7 0
00:18:10 3 0
00:18:00 7 0
00:17:50 0 0
00:16:39 0 0
00:16:29 0 0
Example 7-5 provides sample output from the debug ip ospf monitor command. This
command provides real-time information about when the SPF algorithm is scheduled to
run and when it actually does run.
Example 7-5 debug ip ospf monitor Command Output
R2# debug ip ospf monitor
OSPF spf monitoring debugging is on
*Mar 1 00:29:11.923: OSPF: Schedule SPF in area 0
Change in LS ID 10.1.1.1, LSA type R, , spf-type Full
*Mar 1 00:29:11.927: OSPF: reset throttling to 5000ms
*Mar 1 00:29:11.927: OSPF: schedule SPF: spf_time 00:29:11.928 wait_interval 5000ms
*Mar 1 00:29:16.927: OSPF: Begin SPF at 1756.928ms, process time 1132ms
*Mar 1 00:29:16.927: spf_time 00:29:11.928, wait_interval 5000ms
*Mar 1 00:29:16.947: OSPF: wait_interval 10000ms next wait_interval 10000ms
*Mar 1 00:29:16.947: OSPF: End SPF at 1756.948ms, Total elapsed time 20ms
*Mar 1 00:29:16.951: Schedule time 00:29:16.948, Next wait_interval 10000ms
*Mar 1 00:29:16.955: Intra: 12ms, Inter: 0ms, External: 0ms
*Mar 1 00:29:16.955: R: 4, N: 2, Stubs: 10
*Mar 1 00:29:16.955: SN: 0, SA: 0, X5: 0, X7: 0
*Mar 1 00:29:16.955: SPF suspends: 0 intra, 0 total
*Mar 1 00:29:26.175: OSPF: Schedule SPF in area 0
Change in LS ID 10.1.1.1, LSA type R, , spf-type Full
*Mar 1 00:29:26.947: OSPF: Begin SPF at 1766.948ms, process time 1160ms
*Mar 1 00:29:26.947: spf_time 00:29:16.948, wait_interval 10000ms
*Mar 1 00:29:26.971: OSPF: wait_interval 10000ms next wait_interval 10000ms
*Mar 1 00:29:26.975: OSPF: End SPF at 1766.972ms, Total elapsed time 28ms
*Mar 1 00:29:26.975: Schedule time 00:29:26.972, Next wait_interval 10000ms
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Chapter 7: OSPF and Route Redistribution Troubleshooting 183
*Mar 1 00:29:26.975: Intra: 16ms, Inter: 0ms, External: 0ms
*Mar 1 00:29:26.975: R: 4, N: 2, Stubs: 11
*Mar 1 00:29:26.975: SN: 0, SA: 0, X5: 0, X7: 0
*Mar 1 00:29:26.975: SPF suspends: 0 intra, 0 total
Example 7-6 provides sample output from the debug ip routing command. The output reflects
a loopback interface (with an IP address of 10.1.1.1) on a neighboring router being
administratively shut down and brought back up.
Example 7-6 debug ip routing Command Output
R2# debug ip routing
IP routing debugging is on
*Mar 1 00:29:58.163: RT: del 10.1.1.1/32 via 192.168.0.11, ospf metric [110/11]
*Mar 1 00:29:58.163: RT: delete subnet route to 10.1.1.1/32
*Mar 1 00:29:58.163: RT: NET-RED 10.1.1.1/32
*Mar 1 00:30:08.175: RT: SET_LAST_RDB for 10.1.1.1/32
NEW rdb: via 192.168.0.11
*Mar 1 00:30:08.179: RT: add 10.1.1.1/32 via 192.168.0.11, ospf metric [110/11]
*Mar 1 00:30:08.183: RT: NET-RED 10.1.1.1/32
Example 7-7 provides sample output from the show ip route ospf command. This command
produces a subset of the output from the show ip route command, showing only
those route entries learned via OSPF.
Example 7-7 show ip route ospf Command Output
R2# show ip route ospf
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O 10.1.3.0/30 [110/128] via 172.16.2.2, 00:00:20, Serial1/0.2
[110/128] via 172.16.1.1, 00:00:20, Serial1/0.1
O 10.3.3.3/32 [110/65] via 172.16.1.1, 00:00:20, Serial1/0.1
O 10.1.2.0/24 [110/74] via 172.16.2.2, 00:00:20, Serial1/0.2
[110/74] via 172.16.1.1, 00:00:20, Serial1/0.1
O 10.1.1.1/32 [110/11] via 192.168.0.11, 00:00:20, FastEthernet0/0
O 10.4.4.4/32 [110/65] via 172.16.2.2, 00:00:20, Serial1/0.2
Example 7-8 provides sample output from the debug ip ospf packet command. The output
confirms OSPF packets are being received from specific neighbors and over what interfaces
those OSPF packets are being received. For example, the output indicates that an
OSPF neighbor with a router ID of 10.1.1.1 sent an OSPF packet, and that packet came
into this router on FastEthernet 0/0.
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Example 7-8 debug ip ospf packet Command Output
R2# debug ip ospf packet
OSPF packet debugging is on
*Mar 1 00:30:42.995: OSPF: rcv. v:2 t:1 l:48 rid:10.1.1.1
aid:0.0.0.0 chk:5422 aut:0 auk: from FastEthernet0/0
*Mar 1 00:30:45.039: OSPF: rcv. v:2 t:4 l:76 rid:10.1.1.1
aid:0.0.0.0 chk:E9B4 aut:0 auk: from FastEthernet0/0
*Mar 1 00:30:45.179: OSPF: rcv. v:2 t:1 l:48 rid:10.3.3.3
aid:0.0.0.0 chk:D294 aut:0 auk: from Serial1/0.1
*Mar 1 00:30:45.363: OSPF: rcv. v:2 t:1 l:48 rid:10.4.4.4
aid:0.0.0.0 chk:D192 aut:0 auk: from Serial1/0.2
*Mar 1 00:30:47.727: OSPF: rcv. v:2 t:5 l:44 rid:10.3.3.3
aid:0.0.0.0 chk:2EF0 aut:0 auk: from Serial1/0.1
Example 7-9 provides sample output from the debug ip adj command. This command
shows real-time details as a router establishes an adjacency with an OSPF neighbor, including
the states through which the adjacency transitions.
Example 7-9 debug ip ospf adj Command Output
R2# debug ip ospf adj
OSPF adjacency events debugging is on
*Mar 1 00:31:44.719: OSPF: Rcv LS UPD from 10.3.3.3 on Serial1/0.1 length 100
LSA count 1
*Mar 1 00:31:57.475: OSPF: Cannot see ourself in hello from 10.4.4.4 on
Serial1/0.2, state INIT
*Mar 1 00:31:57.807: OSPF: 2 Way Communication to 10.4.4.4 on Serial1/0.2,
state 2WAY
*Mar 1 00:31:57.811: OSPF: Send DBD to 10.4.4.4 on Serial1/0.2 seq 0x7FD opt
0x52 flag 0x7 len 32
*Mar 1 00:31:57.815: OSPF: Rcv DBD from 10.4.4.4 on Serial1/0.2 seq 0xDF9 opt
0x52 flag 0x7 len 32 mtu 1500 state EXSTART
*Mar 1 00:31:57.819: OSPF: NBR Negotiation Done. We are the SLAVE
*Mar 1 00:31:57.819: OSPF: Send DBD to 10.4.4.4 on Serial1/0.2 seq 0xDF9 opt
0x52 flag 0x2 len 152
*Mar 1 00:31:57.983: OSPF: Build router LSA for area 0, router ID 10.2.2.2, seq
0x80000014
*Mar 1 00:31:58.191: OSPF: Rcv DBD from 10.4.4.4 on Serial1/0.2 seq 0xDFA opt
0x52 flag 0x3 len 152 mtu 1500 state EXCHANGE
*Mar 1 00:31:58.195: OSPF: Send DBD to 10.4.4.4 on Serial1/0.2 seq 0xDFA opt
0x52 flag 0x0 len 32
*Mar 1 00:31:58.199: OSPF: Rcv LS UPD from 10.3.3.3 on Serial1/0.1 length 112
LSA count 1
*Mar 1 00:31:58.455: OSPF: Rcv DBD from 10.4.4.4 on Serial1/0.2 seq 0xDFB opt
0x52 flag 0x1 len 32 mtu 1500 state EXCHANGE
*Mar 1 00:31:58.459: OSPF: Exchange Done with 10.4.4.4 on Serial1/0.2
*Mar 1 00:31:58.463: OSPF: Synchronized with 10.4.4.4 on Serial1/0.2, state FULL
*Mar 1 00:31:58.463: %OSPF-5-ADJCHG: Process 1, Nbr 10.4.4.4 on Serial1/0.2 from
LOADING to FULL, Loading Done
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Example 7-10 provides sample output from the debug ip ospf events command. This command
produces real-time information about OSPF events, including the transmission and
reception of OSPF Hello messages and LSAs.
Example 7-10 debug ip ospf events Command Output
R2# debug ip ospf events
OSPF events debugging is on
*Mar 1 00:32:23.007: OSPF: Rcv hello from 10.1.1.1 area 0 from FastEthernet0/0
192.168.0.11
*Mar 1 00:32:23.011: OSPF: End of hello processing
*Mar 1 00:32:25.195: OSPF: Rcv hello from 10.3.3.3 area 0 from Serial1/0.1
172.16.1.1
*Mar 1 00:32:25.199: OSPF: End of hello processing
*Mar 1 00:32:27.507: OSPF: Rcv hello from 10.4.4.4 area 0 from Serial1/0.2
172.16.2.2
*Mar 1 00:32:27.511: OSPF: End of hello processing
*Mar 1 00:32:28.595: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/0.1 from
172.16.1.2
*Mar 1 00:32:28.687: OSPF: Send hello to 224.0.0.5 area 0 on Serial1/0.2 from
172.16.2.1
*Mar 1 00:32:29.163: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0
from 192.168.0.22
*Mar 1 00:32:32.139: OSPF: Rcv LS UPD from 10.3.3.3 on Serial1/0.1 length 100
LSA count 1
*Mar 1 00:32:33.007: OSPF: Rcv hello from 10.1.1.1 area 0 from FastEthernet0/0
192.168.0.11
*Mar 1 00:32:33.011: OSPF: End of hello processing
*Mar 1 00:32:35.087: OSPF: Rcv hello from 10.3.3.3 area 0 from Serial1/0.1
172.16.1.1
*Mar 1 00:32:35.091: OSPF: End of hello processing
Example 7-11 provides sample output from the show ip ospf virtual-links command. The
output indicates that the other end of the virtual link has an OSPF router ID of 10.2.2.2.
Also, notice that the transit area (that is, the area between the discontiguous area and area
0) is area 1.
Example 7-11 show ip ospf virtual-links Command Output
R1# show ip ospf virtual-links
Virtual Link OSPF_VL5 to router 10.2.2.2 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface FastEthernet0/1, Cost of using 1
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:00
Adjacency State FULL (Hello suppressed)
Index 1/2, retransmission queue length 0, number of retransmission 0
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First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 0, maximum is 0
Last retransmission scan time is 0 msec, maximum is 0 msec
Trouble Ticket: OSPF
This trouble ticket focuses on OSPF. You are presented with baseline data, a trouble
ticket, and information collected while investigating the reported issue. You are then challenged
to identify the issue (or issues) and create an action plan to resolve that issue(s).
Trouble Ticket #4
You receive the following trouble ticket:
For vendor interoperability reasons, a company changed its routing protocol from
EIGRP to OSPF. The network was divided into areas, and all interfaces were instructed
to participate in OSPF. The configuration was initially working. However,
now none of the routers have full reachability to all the subnets.
This trouble ticket references the topology shown in Figure 7-4.
S 1/0.2
.1
Lo 0
10.3.3.3/32 .1
Fa 0/0
S 1/0.2
.1
DLCI = 182
DLCI = 811
S 1/0.1
.1
Lo 0
10.1.1.1/32
Lo 0
10.2.2.2/32
172.16.1.0/30
Fa 0/0
DLCI = 881
.11
FXS
1/0/0
FXS
1/0/1
R2
192.168.1.0/24
192.168.0.0/24
Fa 0/1
.11
172.16.2.0/30
S 1/0.1
.2
DLCI = 882
Fa 0/0
.22
10.1.3.0/30
10.1.2.0/24
Gig 0/8 Fa 5/46
Lo 0
10.4.4.4/32
S 1/0.2
.2
DLCI = 821 .2
Fa 0/0
Gig 0/9 Fa 5/47
Fa 5/45
x3333
Gig 0/10 Fa 5/48
100 Mbps
10 Mbps
R1
BB2
BB1
R2 FRSW
x2222
Area 2 Area 1 Area 0
x1111
SW1 SW2
S 1/0.1
.2
DLCI = 181
Figure 7-4 Trouble Ticket #4 Topology
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Chapter 7: OSPF and Route Redistribution Troubleshooting 187
As you investigate this issue, you examine baseline data collected after OSPF was initially
configured. Example 7-12 shows baseline data collected from router R1, when the network
was fully operational. Notice that router R1 is configured with a virtual link because it
does not physically touch area 0.
Example 7-12 Baseline Configuration Data from Router R1
R1# show run begin router
router ospf 1
area 1 virtual-link 10.2.2.2
network 10.1.1.1 0.0.0.0 area 1
network 192.168.0.0 0.0.0.255 area 1
network 192.168.1.0 0.0.0.255 area 2
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 0 FULL/ - - 192.168.0.22 OSPF_VL2
10.2.2.2 1 FULL/DR 00:00:38 192.168.0.22 FastEthernet0/1
R1# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
O 172.16.1.0 [110/134] via 192.168.0.22, 01:34:44, FastEthernet0/1
O 172.16.2.0 [110/81] via 192.168.0.22, 01:34:44, FastEthernet0/1
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O 10.2.2.2/32 [110/2] via 192.168.0.22, 02:24:31, FastEthernet0/1
O 10.1.3.0/30 [110/145] via 192.168.0.22, 01:34:44, FastEthernet0/1
O 10.3.3.3/32 [110/92] via 192.168.0.22, 01:34:44, FastEthernet0/1
O 10.1.2.0/24 [110/91] via 192.168.0.22, 01:34:45, FastEthernet0/1
C 10.1.1.1/32 is directly connected, Loopback0
O 10.4.4.4/32 [110/82] via 192.168.0.22, 01:34:45, FastEthernet0/1
C 192.168.0.0/24 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
R1# show ip ospf
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Routing Process “ospf 1” with ID 10.1.1.1
Supports only single TOS(TOS0) routes
Supports opaque LSA
Supports Link-local Signaling (LLS)
Supports area transit capability It is an area border router
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Incremental-SPF disabled
Minimum LSA interval 5 secs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Number of external LSA 0. Checksum Sum 0x000000
Number of opaque AS LSA 0. Checksum Sum 0x000000
Number of DCbitless external and opaque AS LSA 0
Number of DoNotAge external and opaque AS LSA 0
Number of areas in this router is 3. 3 normal 0 stub 0 nssa
Number of areas transit capable is 1
External flood list length 0
Area BACKBONE(0)
Number of interfaces in this area is 1
Area has no authentication
SPF algorithm last executed 01:35:17.308 ago
SPF algorithm executed 9 times
Area ranges are
Number of LSA 12. Checksum Sum 0x063B08
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 7
Flood list length 0
Area 1
Number of interfaces in this area is 2 (1 loopback)
This area has transit capability: Virtual Link Endpoint
Area has no authentication
SPF algorithm last executed 02:25:04.377 ago
SPF algorithm executed 22 times
Area ranges are
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Number of LSA 10. Checksum Sum 0x059726
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 2
Number of interfaces in this area is 1
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area has no authentication
SPF algorithm last executed 02:25:15.880 ago
SPF algorithm executed 9 times
Area ranges are
Number of LSA 10. Checksum Sum 0x05F97B
Number of opaque link LSA 0. Checksum Sum 0x000000
Number of DCbitless LSA 0
R1# show ip ospf interface fa0/1
FastEthernet0/1 is up, line protocol is up
Internet Address 192.168.0.11/24, Area 1
Process ID 1, Router ID 10.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 10.2.2.2, Interface address 192.168.0.22
Backup Designated router (ID) 10.1.1.1, Interface address 192.168.0.11
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:00
Supports Link-local Signaling (LLS)
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.2.2.2 (Designated Router)
Suppress hello for 0 neighbor(s)
Example 7-13 shows baseline configuration data collected from router R2.
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Example 7-13 Baseline Configuration Data from Router R2
R2# show run begin router
router ospf 1
area 1 virtual-link 10.1.1.1
network 10.2.2.2 0.0.0.0 area 1
network 172.16.1.0 0.0.0.3 area 0
network 172.16.2.0 0.0.0.3 area 0
network 192.168.0.0 0.0.0.255 area 1
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.4.4.4 0 FULL/ - 00:00:34 172.16.2.2 Serial1/0.2
10.3.3.3 0 FULL/ - 00:00:37 172.16.1.1 Serial1/0.1
10.1.1.1 0 FULL/ - - 192.168.0.11 OSPF_VL0
10.1.1.1 1 FULL/BDR 00:00:39 192.168.0.11 FastEthernet0/0
R2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.1
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
C 10.2.2.2/32 is directly connected, Loopback0
O 10.1.3.0/30 [110/144] via 172.16.2.2, 01:34:50, Serial1/0.2
O 10.3.3.3/32 [110/91] via 172.16.2.2, 01:34:50, Serial1/0.2
O 10.1.2.0/24 [110/90] via 172.16.2.2, 01:34:50, Serial1/0.2
O 10.1.1.1/32 [110/11] via 192.168.0.11, 02:24:36, FastEthernet0/0
O 10.4.4.4/32 [110/81] via 172.16.2.2, 01:34:50, Serial1/0.2
C 192.168.0.0/24 is directly connected, FastEthernet0/0
O IA 192.168.1.0/24 [110/11] via 192.168.0.11, 01:34:50, FastEthernet0/0
R2# show run begin router
router ospf 1
area 1 virtual-link 10.1.1.1
network 10.2.2.2 0.0.0.0 area 1
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network 172.16.1.0 0.0.0.3 area 0
network 172.16.2.0 0.0.0.3 area 0
network 192.168.0.0 0.0.0.255 area 1
Example 7-14 shows baseline configuration data collected from router BB1.
Example 7-14 Baseline Configuration Data from Router BB1
BB1# show run begin router
router ospf 1
network 0.0.0.0 255.255.255.255 area 0
BB1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.4.4.4 1 FULL/DR 00:00:38 10.1.2.2 FastEthernet0/
0
10.2.2.2 0 FULL/ 00:00:39 172.16.1.2 Serial1/0.2
10.4.4.4 0 FULL/ - 00:00:38 10.1.3.2 Serial1/0.1
BB1# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.2
O 172.16.2.0 [110/90] via 10.1.2.2, 01:35:01, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O IA 10.2.2.2/32 [110/91] via 10.1.2.2, 01:35:01, FastEthernet0/0
C 10.1.3.0/30 is directly connected, Serial1/0.1
C 10.3.3.3/32 is directly connected, Loopback0
C 10.1.2.0/24 is directly connected, FastEthernet0/0
O IA 10.1.1.1/32 [110/101] via 10.1.2.2, 01:35:01, FastEthernet0/0
O 10.4.4.4/32 [110/11] via 10.1.2.2, 01:35:01, FastEthernet0/0
O IA 192.168.0.0/24 [110/100] via 10.1.2.2, 01:35:01, FastEthernet0/0
O IA 192.168.1.0/24 [110/101] via 10.1.2.2, 01:35:01, FastEthernet0/0
Example 7-15 shows baseline configuration data collected from router BB2.
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Example 7-15 Baseline Configuration Data from Router BB2
BB2# show run | begin router
router ospf 1
network 0.0.0.0 255.255.255.255 area 0
BB2# show ip ospf neighbor
10.2.2.2 0 FULL/ - 00:00:32 172.16.2.1 Serial1/0.2
10.3.3.3 0 FULL/ - 00:00:39 10.1.3.1 Serial1/0.1
10.3.3.3 1 FULL/BDR 00:00:35 10.1.2.1
FastEthernet0/0
Neighbor ID Pri State Dead Time Address Interface
BB2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
O IA 192.168.1.0/24 [110/101] via 10.1.2.2, 01:35:01, FastEthernet0/0
O 172.16.1.0 [110/143] via 10.1.2.1, 01:35:06, FastEthernet0/0
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O IA 10.2.2.2/32 [110/81] via 172.16.2.1, 01:35:06, Serial1/0.2
C 10.1.3.0/30 is directly connected, Serial1/0.1
O 10.3.3.3/32 [110/11] via 10.1.2.1, 01:35:06, FastEthernet0/0
C 10.1.2.0/24 is directly connected, FastEthernet0/0
O IA 10.1.1.1/32 [110/91] via 172.16.2.1, 01:35:06, Serial1/0.2
C 10.4.4.4/32 is directly connected, Loopback0
O IA 192.168.0.0/24 [110/90] via 172.16.2.1, 01:35:06, Serial1/0.2
O IA 192.168.1.0/24 [110/91] via 172.16.2.1, 01:35:06, Serial1/0.2
Now that you have seen the baseline data, the following examples present you with data
collected after the trouble ticket was issued. Example 7-16 shows information collected
from router R1. Notice that router R1’s routing table can no longer see the Loopback 0 IP
address of router BB2 (that is, 10.4.4.4/32). Also, notice that the virtual link between area
2 and area 0 is down.
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Example 7-16 Information Gathered from Router R1 After the Trouble TicketWas Issued
R1# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
O IA 172.16.1.0 [110/134] via 192.168.0.22, 00:00:31, FastEthernet0/1
O IA 172.16.2.0 [110/81] via 192.168.0.22, 00:00:31, FastEthernet0/1
10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
O 10.2.2.2/32 [110/2] via 192.168.0.22, 00:00:51, FastEthernet0/1
O IA 10.1.3.0/30 [110/198] via 192.168.0.22, 00:00:31, FastEthernet0/1
O IA 10.3.3.3/32 [110/135] via 192.168.0.22, 00:00:31, FastEthernet0/1
O IA 10.1.2.0/24 [110/144] via 192.168.0.22, 00:00:32, FastEthernet0/1
C 10.1.1.1/32 is directly connected, Loopback0
C 192.168.0.0/24 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
R1# show run begin router
router ospf 1
log-adjacency-changes
area 2 virtual-link 10.2.2.2
network 10.1.1.1 0.0.0.0 area 1
network 192.168.0.0 0.0.0.255 area 1
network 192.168.1.0 0.0.0.255 area 2
R1# show ip ospf virtual-links
Virtual Link OSPF_VL4 to router 10.2.2.2 is down
Run as demand circuit
DoNotAge LSA allowed.
Transit area 2, Cost of using 65535
Transmit Delay is 1 sec, State DOWN,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Example 7-17 shows the IP routing table on router R2 after the trouble ticket was issued.
Notice that the routing table of router R1 can no longer see the Loopback 0 IP address of
router BB2 (that is, 10.4.4.4/32). Also, notice that network 192.168.1.0/24, connected to
router R1’s Fast Ethernet 0/0 interface, is not present in router R2’s IP routing table.
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Example 7-17 Router R2’s IP Routing Table After the Trouble Ticket Was Issued
R2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.1
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
C 10.2.2.2/32 is directly connected, Loopback0
O 10.1.3.0/30 [110/197] via 172.16.1.1, 00:00:53, Serial1/0.1
O 10.3.3.3/32 [110/134] via 172.16.1.1, 00:00:53, Serial1/0.1
O 10.1.2.0/24 [110/143] via 172.16.1.1, 00:00:53, Serial1/0.1
O 10.1.1.1/32 [110/11] via 192.168.0.11, 00:00:53, FastEthernet0/0
C 192.168.0.0/24 is directly connected, FastEthernet0/0
Before moving forward to investigate the remainder of the network, do you already see an
issue that needs to be resolved? The fact that router R2 cannot see network 192.168.1.0/24
off of router R1 is independent of any configuration on routers BB1 or BB2. So, take a few
moments to review the information collected thus far, and hypothesize the issue that is
preventing router R2 from seeing network 192.168.1.0/24. On a separate sheet of paper,
write your solution to the issue you identified.
Issue #1: Suggested Solution
The virtual link configuration on router R1 was incorrect. Specifically, the transit area in
the area number virtual-link router-id command was configured as area 2. However, the
transit area should have been area 1. Example 7-18 shows the commands used to correct
this misconfiguration.
Example 7-18 Correcting the Virtual Link Configuration Router of R1
R1# conf term
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#no area 2 virtual-link 10.2.2.2
R1(config-router)#area 1 virtual-link 10.2.2.2
After you correct the virtual link configuration on router R1, network 192.168.1.0/24 is
present in router R2’s IP routing table, as illustrated in Example 7-19. Notice, however, that
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the Loopback 0 IP address of router BB2 (that is, 10.4.4.4/32) is still not visible in router
R2’s IP routing table.
Example 7-19 Router R2’s IP Routing Table After Correcting the Virtual Link
Configuration
R2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.1
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
C 10.2.2.2/32 is directly connected, Loopback0
O 10.1.3.0/30 [110/197] via 172.16.1.1, 00:00:18, Serial1/0.1
O 10.3.3.3/32 [110/134] via 172.16.1.1, 00:00:18, Serial1/0.1
O 10.1.2.0/24 [110/143] via 172.16.1.1, 00:00:18, Serial1/0.1
O 10.1.1.1/32 [110/11] via 192.168.0.11, 00:00:18, FastEthernet0/0
C 192.168.0.0/24 is directly connected, FastEthernet0/0
O IA 192.168.1.0/24 [110/11] via 192.168.0.11, 00:00:18, FastEthernet0/0
With one issue now resolved, continue to collect information on router R2. Example 7-20
indicates that router R2 has not formed an adjacency with router BB2, which has an OSPF
router ID of 10.4.4.4.
Example 7-20 OSPF Neighbors of Router R2
R2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.3.3.3 0 FULL/ - 00:00:37 172.16.1.1 Serial1/0.1
10.1.1.1 0 FULL/ - - 192.168.0.11 OSPF_VL1
10.1.1.1 1 FULL/DR 00:00:39 192.168.0.11 FastEthernet0/0
Example 7-20 shows the OSPF configuration of router R2.
R2# show run begin router
router ospf 2
log-adjacency-changes
area 1 virtual-link 10.1.1.1
network 10.2.2.2 0.0.0.0 area 1
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network 172.16.1.0 0.0.0.3 area 0
network 172.16.2.0 0.0.0.3 area 0
network 192.168.0.0 0.0.0.255 area 1
Even though router R2 has not formed an adjacency with router BB2, Example 7-21 shows
the output of a ping command, verifying that router R2 can reach router BB2.
Example 7-21 Pinging Router BB2 from Router R2
R2# ping 172.16.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 52/92/144 ms
The topology diagram indicates that router R2 connects with router BB2 via subinterface
Serial 1/0.2. Therefore, the show interface s1/0.2 command is issued on router R2. The
output provided in Example 7-22 states that the subinterface is up and functional.
Example 7-22 Serial 1/0.2 Subinterface of Router R2
R2# show interface s1/0.2
Serial1/0.2 is up, line protocol is up
Hardware is M4T
Internet address is 172.16.2.1/30
MTU 1500 bytes, BW 1250 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation FRAME-RELAY
Last clearing of “show interface” counters never
Example 7-23 confirms that router BB2 is adjacent at Layer 2 with router R2.
Example 7-23 CDP Neighbors of Router R2
R2# show cdp neighbor
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
BB1 Ser 1/0.1 152 R S I 2691 Ser 1/0.2
BB2 Ser 1/0.2 143 R S I 2691 Ser 1/0.2
R1 Fas 0/0 144 R S I 2611XM Fas 0/1
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The output of Example 7-24 shows the OSPF status of router R2’s Serial 1/0.2 subinterface.
Example 7-24 OSPF Status of Router R2 on Subinterface Serial 1/0.2
Supports Link-local Signaling (LLS)
Index 3/4, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 4
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
Now that data has been collected for router R2, the troubleshooting focus moves to router
BB1. Notice that BB1 also lacks a route to router BB2’s Loopback 0 IP address of
10.4.4.4/32. Also, even though router BB1 has two direct connections to router BB2,
router BB1 has not formed an OSPF adjacency with router BB2. Notice that router BB2 is
router BB1’s Cisco Discovery Protocol (CDP) neighbor, both on interface FastEthernet 0/0
and on subinterface Serial 1/0.1.
Example 7-25 Data Collected from Router BB1 After the Trouble Ticket
BB1# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.2
O 172.16.2.0 [110/213] via 172.16.1.2, 00:01:02, Serial1/0.2
10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
O IA 10.2.2.2/32 [110/134] via 172.16.1.2, 00:01:02, Serial1/0.2
C 10.1.3.0/30 is directly connected, Serial1/0.1
C 10.3.3.3/32 is directly connected, Loopback0
C 10.1.2.0/24 is directly connected, FastEthernet0/0
O IA 10.1.1.1/32 [110/144] via 172.16.1.2, 00:01:02, Serial1/0.2
O IA 192.168.0.0/24 [110/143] via 172.16.1.2, 00:01:02, Serial1/0.2
BB1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 0 FULL/ - 00:00:30 172.16.1.2 Serial1/0.2
BB1# show run begin router
router ospf 1
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log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
BB1# show cdp neigh
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
BB2 Ser 1/0.1 148 R S I 2691 Ser 1/0.1
BB2 Fas 0/0 148 R S I 2691 Fas 0/0
R2 Ser 1/0.2 130 R S I 2691 Ser 1/0.1
BB1# show run
...OUTPUT OMITTED...
interface FastEthernet0/0
ip address 10.1.2.1 255.255.255.0
ip ospf network non-broadcast
duplex auto
speed auto
!
interface Serial1/0
no ip address
encapsulation frame-relay
!
interface Serial1/0.1 point-to-point
ip address 10.1.3.1 255.255.255.252
ip ospf hello-interval 60
ip ospf dead-interval 200
frame-relay interface-dlci 881
!
interface Serial1/0.2 point-to-point
bandwidth 750
ip address 172.16.1.1 255.255.255.252
frame-relay interface-dlci 811
...OUTPUT OMITTED...
The data collection continues on router BB2. Example 7-26 provides output from several
show commands. Notice that router BB2 has not learned networks via OSPF.
Based on the preceding show command output from routers R2, BB1, and BB2, hypothesize
what you consider to be the issue or issues still impacting the network. Then, on a
separate sheet of paper, write how you would solve the identified issue or issues.
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Example 7-26 Data Collected from Router BB2 After the Trouble Ticket
BB2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 1 subnets
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
C 10.1.3.0/30 is directly connected, Serial1/0.1
C 10.1.2.0/24 is directly connected, FastEthernet0/0
C 10.4.4.4/32 is directly connected, Loopback0
BB2# show run begin router
router ospf 1
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
BB2# show ip ospf interface s1/0.1
Serial1/0.1 is up, line protocol is up
Internet Address 10.1.3.2/30, Area 0
Process ID 1, Router ID 10.4.4.4, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:09
Supports Link-local Signaling (LLS)
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 3
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
BB2# show ip ospf interface s1/0.2
Serial1/0.2 is up, line protocol is up
Internet Address 172.16.2.2/30, Area 0
Process ID 1, Router ID 10.4.4.4, Network Type NON_BROADCAST, Cost: 80
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 10.4.4.4, Interface address 172.16.2.2
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No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
oob-resync timeout 120
Hello due in 00:00:09
Supports Link-local Signaling (LLS)
Index 3/3, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
!
interface FastEthernet0/0
ip address 10.1.2.2 255.255.255.0
!
interface Serial1/0
no ip address
encapsulation frame-relay
!
interface Serial1/0.1 point-to-point
ip address 10.1.3.2 255.255.255.252
frame-relay interface-dlci 882
!
interface Serial1/0.2 point-to-point
bandwidth 1250
ip address 172.16.2.2 255.255.255.252
ip ospf network non-broadcast
frame-relay interface-dlci 821
!
...OUTPUT OMITTED...
Issue #2: Suggested Solution
Subinterface Serial 1/0.1 on router BB1 had nondefault Hello and Dead timers, which did
not match the timers at the far end of the Frame Relay link. Example 7-27 illustrates how
these nondefault values were reset.
Example 7-27 Correcting the Nondefault Timer Configuration of Router BB1
BB1# conf term
Enter configuration commands, one per line. End with CNTL/Z.
BB1(config)#int s1/0.1
BB1(config-subif)#no ip ospf hello-interval 60
BB1(config-subif)#no ip ospf dead-interval 200
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Issue #3: Suggested Solution
Interface FastEthernet 0/0 on router BB1 was configured with an incorrect OSPF network
type of nonbroadcast. Example 7-28 demonstrates how this OSPF interface was reset to
its default OSPF network type (that is, the broadcast OSPF network type).
Example 7-28 Correcting the Incorrect OSPFNetwork Type Configuration of Router BB1
BB1# conf term
Enter configuration commands, one per line. End with CNTL/Z.
BB1(config)#int fa 0/0
BB1(config-if)#no ip ospf network non-broadcast
Issue #4: Suggested Solution
Similar to the incorrect OSPF network type on router BB1’s FastEthernet 0/0 interface, the
Serial 1/0.2 subinterface on router BB2 was configured incorrectly. A point-to-point Frame
Relay subinterface defaults to an OSPF network type of point-to-point; however, Serial
1/0.2 had been configured as an OSPF network type of nonbroadcast. Example 7-29 reviews
how this nondefault OSPF network type configuration was removed.
Example 7-29 Correcting Router BB2’s Incorrect OSPF Network Type Configuration
BB2# conf term
Enter configuration commands, one per line. End with CNTL/Z.
BB2(config)#int s1/0.2
BB2(config-subif)#no ip ospf network non-broadcast
After all of the previous misconfigurations are corrected, all routers in the topology once
again have full reachability throughout the network. Examples 7-30, 7-31, 7-32, and 7-33
show output from the show ip route and show ip ospf neighbor commands issued on all
routers, confirming the full reachability of each router.
Example 7-30 Confirming the Full Reachability of Router R1
R1# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
O 172.16.1.0 [110/134] via 192.168.0.22, 00:00:03, FastEthernet0/1
O 172.16.2.0 [110/81] via 192.168.0.22, 00:00:03, FastEthernet0/1
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10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O 10.2.2.2/32 [110/2] via 192.168.0.22, 00:08:18, FastEthernet0/1
O 10.1.3.0/30 [110/145] via 192.168.0.22, 00:00:03, FastEthernet0/1
O 10.3.3.3/32 [110/92] via 192.168.0.22, 00:00:03, FastEthernet0/1
O 10.1.2.0/24 [110/91] via 192.168.0.22, 00:00:04, FastEthernet0/1
C 10.1.1.1/32 is directly connected, Loopback0
O 10.4.4.4/32 [110/82] via 192.168.0.22, 00:00:04, FastEthernet0/1
C 192.168.0.0/24 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 0 FULL/ - - 192.168.0.22 OSPF_VL5
10.2.2.2 1 FULL/BDR 00:00:34 192.168.0.22 FastEthernet0/1
Example 7-31 Confirming the Full Reachability of Router R2
R2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.1
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
C 10.2.2.2/32 is directly connected, Loopback0
O 10.1.3.0/30 [110/144] via 172.16.2.2, 00:00:15, Serial1/0.2
O 10.3.3.3/32 [110/91] via 172.16.2.2, 00:00:15, Serial1/0.2
O 10.1.2.0/24 [110/90] via 172.16.2.2, 00:00:15, Serial1/0.2
O 10.1.1.1/32 [110/11] via 192.168.0.11, 00:08:29, FastEthernet0/0
O 10.4.4.4/32 [110/81] via 172.16.2.2, 00:00:15, Serial1/0.2
C 192.168.0.0/24 is directly connected, FastEthernet0/0
O IA 192.168.1.0/24 [110/11] via 192.168.0.11, 00:00:15, FastEthernet0/0
R2# show ip ospf neighbor
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Neighbor ID Pri State Dead Time Address Interface
10.4.4.4 0 FULL/ - 00:00:33 172.16.2.2 Serial1/0.2
10.3.3.3 0 FULL/ - 00:00:38 172.16.1.1 Serial1/0.1
10.1.1.1 0 FULL/ - - 192.168.0.11 OSPF_VL1
10.1.1.1 1 FULL/DR 00:00:30 192.168.0.11 FastEthernet0/0
Example 7-32 Confirming the Full Reachability of Router BB1
BB1# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
C 172.16.1.0 is directly connected, Serial1/0.2
O 172.16.2.0 [110/90] via 10.1.2.2, 00:00:29, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O IA 10.2.2.2/32 [110/91] via 10.1.2.2, 00:00:29, FastEthernet0/0
C 10.1.3.0/30 is directly connected, Serial1/0.1
C 10.3.3.3/32 is directly connected, Loopback0
C 10.1.2.0/24 is directly connected, FastEthernet0/0
O IA 10.1.1.1/32 [110/101] via 10.1.2.2, 00:00:29, FastEthernet0/0
O 10.4.4.4/32 [110/11] via 10.1.2.2, 00:00:29, FastEthernet0/0
O IA 192.168.0.0/24 [110/100] via 10.1.2.2, 00:00:29, FastEthernet0/0
O IA 192.168.1.0/24 [110/101] via 10.1.2.2, 00:00:29, FastEthernet0/0
BB1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.4.4.4 1 FULL/DR 00:00:34 10.1.2.2 FastEthernet0/
10.2.2.2 0 FULL/ - 00:00:39 172.16.1.2 Serial1/0.2
10.4.4.4 0 FULL/ - 00:00:33 10.1.3.2 Serial1/0.1
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Example 7-33 Confirming the Full Reachability of Router BB2
BB2# 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/30 is subnetted, 2 subnets
O 172.16.1.0 [110/143] via 10.1.2.1, 00:00:42, FastEthernet0/0
C 172.16.2.0 is directly connected, Serial1/0.2
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
O IA 10.2.2.2/32 [110/81] via 172.16.2.1, 00:00:42, Serial1/0.2
C 10.1.3.0/30 is directly connected, Serial1/0.1
O 10.3.3.3/32 [110/11] via 10.1.2.1, 00:00:42, FastEthernet0/0
C 10.1.2.0/24 is directly connected, FastEthernet0/0
O IA 10.1.1.1/32 [110/91] via 172.16.2.1, 00:00:42, Serial1/0.2
C 10.4.4.4/32 is directly connected, Loopback0
O IA 192.168.0.0/24 [110/90] via 172.16.2.1, 00:00:42, Serial1/0.2
O IA 192.168.1.0/24 [110/91] via 172.16.2.1, 00:00:42, Serial1/0.2
BB2# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 0 FULL/ - 00:00:38 172.16.2.1 Serial1/0.2
10.3.3.3 0 FULL/ - 00:00:29 10.1.3.1 Serial1/0.1
10.3.3.3 1 FULL/BDR 00:00:34 10.1.2.1 FastEthernet0/0
Route Redistribution Troubleshooting
Route redistribution allows routes learned via one method (for example, statically configured,
locally connected, or learned via a routing protocol) to be injected into a different
routing protocol. If two routing protocols are mutually redistributed, the routes learned
via each routing protocol are injected into the other routing protocol.
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A network might benefit from route redistribution in the following scenarios:
■ Transitioning to a more advanced routing protocol
■ Merger of companies
■ Different areas of administrative control
Route Redistribution Overview
A router that sits at the boundary of the routing domains to be redistributed is known as a
boundary router, as illustrated in Figure 7-5. A boundary router can redistribute static
routes, connected routes, or routes learned via one routing protocol into another routing
protocol.
Different routing protocols use different types of metrics, as illustrated in Figure 7-6.
Therefore, when a route is injected into a routing protocol, a metric used by the destination
routing protocol needs to be associated with the route being injected.
The metric assigned to a route being injected into another routing process is called a seed
metric. The seed metric is needed to communicate relative levels of reachability between
dissimilar routing protocols. A seed metric can be defined in one of three ways:
■ The default-metric command
■ The metric parameter in the redistribute command
■ A route map configuration
Key
Topic
Key
Topic
RIP
Boundary Router
EIGRP
R1 R2 R3
Figure 7-5 Boundary Router
RIP
Hop Count Bandwidth, Delay,
Reliability, Load, MTU
EIGRP
R1 R2 R3
Figure 7-6 Differing Metric Parameters Between Routing Protocols
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If a seed metric is not specified, a default seed metric is used. Keep in mind, however, that
RIP and EIGRP have a default metric that is considered unreachable. Therefore, if you do
not configure a nondefault seed metric when redistributing routes into RIP or EIGRP, the
redistributed route will not be reachable.
Some routing protocols (for example, EIGRP, OSPF, and Intermediate System-to-Intermediate
System [IS-IS]) can tag routes as either internal (that is, routes locally configured or
connected) or external (that is, routes learned by another routing process) and give priority
to internal routes versus external routes. The capability to distinguish between internal
and external routes can help prevent a potential routing loop, where two routing protocols
continually redistribute a route into one another.
As described in Chapter 6, a routing protocol can send routes into and learn routes from a
router’s IP routing table, as depicted in Figure 7-7.
If a router is running two routing protocols, however, the routing protocols do not exchange
routes directly between themselves. Rather, only routes in a router’s IP routing
table can be redistributed, as seen in Figure 7-8.
Two prerequisites must be met for the routes of one IP routing protocol to be redistributed
into another IP routing protocol:
■ A route needs to be installed in a router’s IP routing table.
■ The destination IP routing protocol needs a reachable metric to assign to the redistributed
routes.
Route Redistribution Troubleshooting Targets
Effective troubleshooting of route redistribution requires knowledge of verification and
troubleshooting commands for each routing protocol. Table 7-9 identifies troubleshooting
targets to investigate when working to resolve a route redistribution issue.
Incoming Route Information Outgoing Route Information
Data
Structure
of IP
Routing
Protocol
IP
Routing
Table
Redistributed Routes
Injected Routes
Route Installation
Figure 7-7 Routing Data Structures
Key
Topic
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Chapter 7: OSPF and Route Redistribution Troubleshooting 207
Incoming Route Information Outgoing Route Information
Data
Structure
of IP
Routing
Protocol
Data
Structure
of IP
Routing
Protocol
IP
Routing
Table
Route Installation
Redistributed Routes
Injected Routes
Figure 7-8 Route Redistribution Between Two IP Routing Protocols
Table 7-9 Troubleshooting Targets for Route Redistribution
Troubleshooting
Target
Troubleshooting Recommendation
Source routing
protocol
Verify that a route to be redistributed from a routing protocol has been
learned by that routing protocol. Therefore, you can issue appropriate
show commands for the data structures of the source routing protocol to
ensure that the source routing protocol has learned the route in question.
Route selection Because a route must be in a router’s IP routing table to be redistributed,
you should ensure that the routes of the source routing protocol are indeed
being injected into the router’s IP routing table.
Redistribution
configuration
If a route has been injected into a router’s IP routing table from a source
routing protocol but not redistributed into the destination routing protocol,
you should check the redistribution configuration. This involves checking
the metric applied to routes as they are redistributed into the destination
routing protocol, checking for any route filtering that might be preventing
redistribution, and checking the redistribution syntax to confirm the correct
routing process ID or autonomous system number is specified.
Destination
routing protocol
If a route has been successfully redistributed into a destination routing protocol
but the route has not been successfully learned by neighboring routers,
you should investigate the destination routing protocol.You could use traditionalmethods
of troubleshooting a destination routing protocol; however,
keep in mind that the redistributed route might be marked as an external
route. Therefore, check the characteristics of the destination routing protocol
to determine if it treats external routes differently frominternal ones.
Key
Topic
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Although the previously discussed debug ip routing command can provide insight into
routing loops that might be occurring, you can also use the Cisco IOS IP route profiling
feature to troubleshoot route instability. Route profiling can be enabled in global configuration
mode with the ip route profile command. Example 7-34 provides sample output
from the show ip route profile command, which is used to view the information collected
from the IP route profiling feature.
Example 7-34 show ip route profile Command Output
Key
Topic
R4# show ip route profile
IP routing table change statistics:
Frequency of changes in a 5 second sampling interval
-------------------------------------------------------------
Change/ Fwd-path Prefix Nexthop Pathcount Prefix
interval change add change change refresh
-------------------------------------------------------------
0 38 38 41 41 41
1 3 3 0 0 0
2 0 0 0 0 0
3 0 0 0 0 0
4 0 0 0 0 0
5 0 0 0 0 0
10 0 0 0 0 0
15 0 0 0 0 0
20 0 0 0 0 0
25 0 0 0 0 0
30 0 1 0 1 0
55 0 0 0 0 0
80 0 0 0 0 0
105 0 0 0 0 0
130 0 0 0 0 0
155 0 0 0 0 0
280 0 0 0 0 0
405 0 0 0 0 0
530 0 0 0 0 0
655 0 0 0 0 0
780 0 0 0 0 0
1405 0 0 0 0 0
2030 0 0 0 0 0
2655 0 0 0 0 0
3280 0 0 0 0 0
3905 0 0 0 0 0
7030 0 0 0 0 0
10155 0 0 0 0 0
13280 0 0 0 0 0
Overflow 0 0 0 0 0
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Chapter 7: OSPF and Route Redistribution Troubleshooting 209
The IP route profiling feature measures the number and type of IP routing table
updates every 5 seconds. The left column in the output of the show ip route profile
command represents the number of changes that occurred during a 5-second interval.
As an example, consider the row in the output that has a 30 in the left column. The
number 1 under the Prefix Add column indicates that during one 5-second interval,
30–54 prefixes were added to the IP routing table. The range of 30–54 was
determined by examining the output. Notice that the next value in the Change/
Interval column after 30 is 55. Therefore, a number appearing in the 30 row indicates
during how many 5-second timing intervals a particular IP routing update occurred
30–54 times.
Ideally, only numbers in the first row (that is, the 0 row) should change in a stable network.
If numbers in other rows change, a routing loop might be occurring.
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