troubleshooting ospf notes from routing tcp
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Troubleshooting OSPF notes from Routing TCP/IP vol2
Troubleshooting OSPF Neighbor Relationships
OSPF neighbor relationship problems can be of any of these types:
The OSPF neighbor list is empty.
An OSPF neighbor is stuck in ATTEMPT.
An OSPF neighbor is stuck in INIT.
An OSPF neighbor is stuck in 2-WAY.
An OSPF neighbor is stuck in EXSTART/EXCHANGE.
An OSPF neighbor is stuck in LOADING.
Problem: OSPF Neighbor List Is Empty
The most common possible causes of this problem are as follows:
OSPF is not enabled on the interface.
Layer 1/2 is down.
The interface is defined as passive under OSPF.
An access list is blocking OSPF Hellos on both sides.
A subnet number/mask has been mismatched over a broadcast link.
The Hello/dead interval has been mismatched.
The authentication type (plain text versus MD5) has been mismatched.
An authentication key has been mismatched.
An area ID has been mismatched.
Stub/transit/NSSA area options have been mismatched.
An OSPF adjacency exists with secondary IP addressing.
An OSPF adjacency exists over an asynchronous interface.
No network type or neighbor is defined over NBMA (Frame Relay, X.25, SMDS, and so
on).
The frame-relay map/dialer map statement is missing the broadcast keyword on both
sides
Problem: OSPF Neighbor Stuck in INIT
The most common possible causes of this problem are as follows:
An access list on one side is blocking OSPF Hellos.
Multicast capabilities are broken on one side (6500 switch problem).
Authentication is enabled on only one side (virtual link example).
The frame-relay map/dialer map statement on one side is missing the broadcast keyword.
Hellos are getting lost on one side at Layer 2.
Problem: OSPF Neighbor Stuck in 2-WAY—Cause: Priority 0 Is Configured on All
Routers
Problem: OSPF Neighbor Stuck in EXSTART/EXCHANGE
The most common possible causes of this problem are as follows:
Mismatched interface MTU
Duplicate router IDs on neighbors
Inability to ping across with more than certain MTU size
Broken unicast connectivity because of the following:
- Wrong VC/DLCI mapping in Frame Relay/ATM switch
- Access list blocking the unicast
- NAT translating the unicast
Network type of point-to-point between PRI and BRI/dialer
Problem: OSPF Neighbor Stuck in LOADING
The most common possible causes of this problem are as follows:
Mismatched MTU
Corrupted link-state request packet
Troubleshooting OSPF Route Advertisement
The most common reasons for OSPF to not share the database information about a specific link
are as follows:
The OSPF neighbor is not advertising routes.
The OSPF neighbor (ABR) is not advertising the summary route.
The OSPF neighbor is not advertising external routes.
The OSPF neighbor is not advertising the default route.
Problem: OSPF Neighbor Is Not Advertising Routes
The most common possible causes of this problem are as follows:
OSPF is not enabled on the interface that is supposed to be advertised.
The advertising interface is down.
The secondary interface is in a different area than the primary interface.
Problem: OSPF Neighbor (ABR) Not Advertising the Summary Route
The most common possible causes of this problem are as follows:
An area is configured as a totally stubby area.
An ABR is not connected to area 0.
A discontiguous area 0 exists.
Problem: OSPF Neighbor Is Not Advertising External Routes
The most common possible causes of this problem are as follows:
The area is configured as a stub or NSSA.
The NSSA ABR is not translating Type 7 into Type 5 LSA.
Problem: OSPF Neighbor Not Advertising Default Routes
The most common possible causes for an OSPF router not to advertise the default route are as
follows:
The default-information originate command is missing.
The default route is missing from the neighbor’s routing table.
A neighbor is trying to originate a default into a stub area.
The NSSA ABR/ASBR is not originating the Type 7 default.
Troubleshooting OSPF Route Installation
The most common reasons for OSPF failing to install routes in the routing table are as follows:
OSPF is not installing any routes in the routing table.
OSPF is not installing external routes in the routing table.
Problem: OSPF Not Installing Any Routes in the Routing Table
The most common possible causes of this problem are as follows:
The network type is mismatched.
IP addresses are flipped in dual serial-connected routers or a subnet/mask mismatch has
occurred.
One side is a numbered and the other side is an unnumbered point-to-point link.
A distribute list is blocking the routes’ installation.
There is a broken PVC in a fully meshed Frame Relay network with the broadcast
network type.
Problem: OSPF Not Installing External Routes in the Routing Table
The most common causes of this problem are as follows:
The forwarding address is not known through the intra-area or interarea route.
The ABR is not generating Type 4 summary LSAs.
Troubleshooting Redistribution Problems in OSPF
The following are problems that can happen during redistribution:
ASBR is not advertising redistributed routes.
OSPF is not installing external routes in the routing table.
Problem: OSPF Neighbor Is Not Advertising External Routes
The most common causes of this problem are as follows:
The subnets keyword is missing from the ASBR configuration.
distribute-list out is blocking the routes.
Troubleshooting Route Summarization in OSPF
OSPF can use two types of summarization:
Interarea summarization that can be done on the ABR
External summarization that can be done on the ASBR
Two common problems related to summarization in OSPF are as follows:
A router is not summarizing interarea routes.
A router is not summarizing external routes.
Problem: Router Is Not Summarizing Interarea Routes
—Cause: area range Command Is Not Configured on ABR
Problem: Router Is Not Summarizing External Routes
—Cause: summary-address Command Is Not Configured on ASBR
Troubleshooting CPU HOG Problems
The CPUHOG messages usually appear in two significant stages:
Neighbor formation process
LSA refresh process
This section discusses the possible solutions for these two instances of SPF:
CPUHOG messages during adjacency formation
CPUHOG messages during LSA refresh period
Problem: CPUHOG Messages During Adjacency Formation
—Cause: Router Is Not Running Packet-Pacing Code
Problem: CPUHOG Messages During LSA Refresh Period
—Cause: Router Is Not Running LSA Group-Pacing Code
Troubleshooting SPF Calculation and Route Flapping
The problem of SPF running constantly in the network for the following reasons:
Interface flap within the network
Neighbor flap within the network
Duplicate router ID
Common OSPF Error Messages
“Unknown routing protocol” Error Message = the software or the hardware does not support
OSPF
OSPF: “Could not allocate router id” Error Message =
This message appears in two situations:
No up/up interface with a valid IP address
Not enough up interfaces with a valid IP address for multiple OSPF processes
“%OSPF-4-BADLSATYPE: Invalid lsa: Bad LSA type” Type 6 Error Message
This is normal if the neighboring router is sending the multicast OSPF (MOSPF) packet. For
more information on MOSPF, refer to RFC 1584. Cisco routers do not support MOSPF, so they
simply ignore it
ignore lsa mospf
“OSPF-4-ERRRCV” Error Message
Three common types of this message can occur:
Mismatch area ID
Bad checksum
OSPF not enabled on the receiving interface