Problem: OSPF Neighbor Is Not Advertising Routes

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When a neighbor doesn't advertise a route, that route will not show up in the local router's routing table. This means that the neighbor has not included the route in its database; otherwise , the local router must have received it.

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.

Figure 9-45 shows an OSPF network setup used to produce this problem.

Figure 9-45. OSPF Network Where Routes Are Not Being Advertised Successfully

graphics/09fig45.gif

Example 9-118 shows the output of show ip route 131.108.3.0, which indicates that the route is missing from the routing table of R2.

Example 9-118 R2's Routing Table Is Missing Route 131.108.3.0
   R2#show ip route 131.108.3.0    % Network not in table  R2# 

OSPF Neighbor Is Not Advertising Routes ‚ Cause: OSPF Not Enabled on the Interface That Is Supposed to Be Advertised

OSPF includes the interface subnet address in its database only if the OSPF is enabled on that interface. OSPF might not be enabled on an interface because of an incorrect network state-ment that doesn't cover the IP address assigned on an interface or a missing network statement for that interface address. In both cases, OSPF will exclude the interface address from its data-base and will not advertise to its neighbor.

Figure 9-46 shows the flowchart to follow to solve this problem.

Figure 9-46. Problem-Resolution Flowchart

graphics/09fig46.gif

Debugs and Verification

Example 9-119 shows the output of show ip ospf database router for R1, which indicates that the network 131.108.3.0/24 is missing from the database.

Example 9-119 R1's Database Is Missing 131.108.3.0
 R1#  show ip ospf database router 131.108.2.1  OSPF Router with ID (131.108.1.2) (Process ID 1)                 Router Link States (Area 0)   LS age: 301   Options: (No TOS-capability, DC)   LS Type: Router Links   Link State ID: 131.108.2.1   Advertising Router: 131.108.2.1   LS Seq Number: 80000148   Checksum: 0x1672   Length: 48    Number of Links: 2     Link connected to: another Router (point-to-point)      (Link ID) Neighboring Router ID: 131.108.1.2      (Link Data) Router Interface address: 131.108.1.1       Number of TOS metrics: 0        TOS 0 Metrics: 64     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.1.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0        TOS 0 Metrics: 0     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.2.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0       TOS 0 Metrics: 10 

Example 9-120 shows the output of show ip ospf interface e0 on R1, which indicates that OSPF is not enabled on the interface. In Cisco IOS Software Release 12.0 and later, the output will not display anything if OSPF is not enabled on the interface.

Example 9-120 R1 Does Not Have OSPF Enabled on the Ethernet 0 Interface
 R1#  show ip ospf interface Ethernet 0  Ethernet0 is up, line protocol is up  OSPF not enabled on this interface  

Example 9-121 shows the configuration of R1, which shows that the network statement for 131.108.3.0/24 is missing from the configuration.

Example 9-121 R1's Configuration Is Missing a network Statement for 131.108.3.0
 R1#  router ospf 1   network 131.108.1.0 0.0.0.255 area 0   network 131.108.2.0 0.0.0.255 area 0  
Solution

R1 is not advertising its Ethernet 0 interface in its router LSA. The database output verifies that the Ethernet subnet is not being advertised.

The problem is that the network statement on R1 for the Ethernet interface is incorrect or the network statement is missing from the configuration. In this case, OSPF will not include that particular interface into the router LSA; when R2 receives the router LSA, this particular link is not included in it.

To solve this problem, make sure that the network statement is correct so that R1 includes 131.108.3.0/24 in its router LSA.

Example 9-122 shows that correct configuration that solves this problem.

Example 9-122 Correcting R1's Configuration to Enable OSPF on 131.108.3.0/24
 R1#  router ospf 1   network 131.108.1.0 0.0.0.255 area 0   network 131.108.2.0 0.0.0.255 area 0   network 131.108.3.0 0.0.0.255 area 0  

Example 9-123 shows the router LSA of R1 after fixing this problem. The router LSA shows 131.108.3.0 now as a stub link.

Example 9-123 Network 131.108.3.0/24 Now Appears in the OSPF Database
 1#  show ip ospf database router 131.108.2.1  OSPF Router with ID (131.108.1.2) (Process ID 1)                 Router Link States (Area 0)   LS age: 301   Options: (No TOS-capability, DC)   LS Type: Router Links   Link State ID: 131.108.2.1   Advertising Router: 131.108.2.1   LS Seq Number: 80000148   Checksum: 0x1672   Length: 48    Number of Links: 2     Link connected to: another Router (point-to-point)      (Link ID) Neighboring Router ID: 131.108.1.2      (Link Data) Router Interface address: 131.108.1.1       Number of TOS metrics: 0        TOS 0 Metrics: 64     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.1.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0        TOS 0 Metrics: 0 R     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.2.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0        TOS 0 Metrics: 10  Link connected to: a Stub Network   (Link ID) Network/subnet number: 131.108.3.0   (Link Data) Network Mask: 255.255.255.0  Number of TOS metrics: 0       TOS 0 Metrics: 10 

Example 9-124 shows the output of show ip route 131.108.3.0, which indicates that after fixing this problem, the route shows up in the routing table again.

Example 9-124 Verifying That the 131.108.3.0 Route Is Operational Again
 R2#  show ip route 131.108.3.0   Routing entry for 131.108.3.0/24   Known via "ospf 1", distance 110, metric 64, type intra area  Redistributing via ospf 1   Last update from 131.108.1.1 on Serial0, 04:22:21 ago   Routing Descriptor Blocks:   * 131.108.1.1, from 131.108.2.1, 04:22:21 ago, via Serial0      Route metric is 64, traffic share count is 1 

OSPF Neighbor Is Not Advertising Routes ‚ Cause: Advertising Interface Is Down

OSPF does not advertise a network that is down. If an interface is down, the network assigned to that interface is not advertised in a router's LSA.

Figure 9-47 shows the flowchart to follow to solve this problem.

Figure 9-47. Problem-Resolution Flowchart

graphics/09fig47.gif

Debugs and Verification

Recall from Figure 9-45 that the Ethernet 0 address is 131.108.3.0/24. If this interface is down, it will not be advertised in the OSPF database.

Example 9-125 shows the output of show ip ospf interface for Ethernet 0, which indicates that the line protocol is down.

Example 9-125 show ip ospf interface Command Output Determines Line Protocol Status of Ethernet 0 on R1
 R1#  show ospf interface Ethernet 0  Ethernet0 is up,  line protocol is down  Internet Address 131.108.3.1/24, Area 0   Process ID 1, Router ID 131.108.2.1, Network Type BROADCAST, Cost: 10   Transmit Delay is 1 sec, State DOWN, Priority 1   No designated router on this network   No backup designated router on this network   Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 

Example 9-126 shows that the Ethernet 0 network address of 131.108.3.0/24 is not listed in the router LSA of R1.

Example 9-126 R1's Ethernet 0 Interface Is Missing from R1's LSA
 R2#  show ip ospf database router 131.108.2.1  OSPF Router with ID (131.108.1.2) (Process ID 1)                 Router Link States (Area 0)   LS age: 301   Options: (No TOS-capability, DC)   LS Type: Router Links   Link State ID: 131.108.2.1   Advertising Router: 131.108.2.1   LS Seq Number: 80000148   Checksum: 0x1672   Length: 48    Number of Links: 2     Link connected to: another Router (point-to-point)      (Link ID) Neighboring Router ID: 131.108.1.2      (Link Data) Router Interface address: 131.108.1.1       Number of TOS metrics: 0        TOS 0 Metrics: 64     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.1.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0        TOS 0 Metrics: 0     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.2.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0       TOS 0 Metrics: 10 
Solution

To fix this problem, bring up the Ethernet 0 interface. Example 9-127 shows the interface statistics after fixing the Layer 2 problem. Some suggestions on fixing the Layer 2 problem were discussed earlier in this chapter in the section "OSPF Neighbor List Is Empty ‚ Cause: Layer 1/2 Is Down."

Example 9-127 Verifying That the Line Protocol Is Back Up for an Interface
 R1#  show ip ospf interface Ethernet 0  Ethernet0 is up,  line protocol is up  Internet Address 131.108.3.1/24, Area 0   Process ID 1, Router ID 131.108.2.1, Network Type BROADCAST, Cost: 10 

Example 9-128 shows the output of show ip route 131.108.3.0, which shows that after fixing this problem, the route came back in the routing table.

Example 9-128 Verifying That the 131.108.3.0 Route Is Operational Again
 R2#  show ip route 131.108.3.0   Routing entry for 131.108.3.0/24   Known via "ospf 1", distance 110, metric 64, type intra area  Redistributing via ospf 1   Last update from 131.108.1.1 on Serial0, 04:22:21 ago   Routing Descriptor Blocks:   * 131.108.1.1, from 131.108.2.1, 04:22:21 ago, via Serial0       Route metric is 64, traffic share count is 1 R2# 

OSPF Neighbor Is Not Advertising Routes ‚ Cause: Secondary Interface Is in a Different Area Than the Primary Interface

When dealing with secondary addresses, OSPF requires the secondary address to belong to the same area as the primary address. If this is not followed, OSPF will not advertise the secondary address in its router LSA.

Figure 9-48 shows the network setup used to produce this problem.

Figure 9-48. OSPF Network Setup Used to Produce Secondary Address/LSA Problems

graphics/09fig48.gif

Figure 9-49 shows the flowchart to follow to solve this problem.

Figure 9-49. Problem-Resolution Flowchart

graphics/09fig49.gif

Debugs and Verification

Example 9-129 shows the router LSA information of R1. The LSA shows that 131.108.3.0/24 is not included in the database. R1 generates the router LSA for area 2, but because the second-ary address is the only address in area 2, the number of the link is 0. This is because the secondary interface address cannot be put into a separate area than the primary interface address.

Example 9-129 Displaying R1's Router LSA Information
 R1#  show ip ospf database router 131.108.2.1  OSPF Router with ID (131.108.1.2) (Process ID 1)                 Router Link States (Area 0)   LS age: 301   Options: (No TOS-capability, DC)   LS Type: Router Links   Link State ID: 131.108.2.1   Advertising Router: 131.108.2.1   LS Seq Number: 80000148   Checksum: 0x1672   Length: 48    Number of Links: 2     Link connected to: another Router (point-to-point)      (Link ID) Neighboring Router ID: 131.108.1.2      (Link Data) Router Interface address: 131.108.1.1       Number of TOS metrics: 0        TOS 0 Metrics: 64     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.1.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0        TOS 0 Metrics: 0     Link connected to: a Stub Network      (Link ID) Network/subnet number: 131.108.2.0      (Link Data) Network Mask: 255.255.255.0       Number of TOS metrics: 0        TOS 0 Metrics: 10  Router Link States (Area 2)  LS age: 39   Options: (No TOS-capability, DC)   LS Type: Router Links   Link State ID: 131.108.2.1   Advertising Router: 131.108.2.1   LS Seq Number: 800001B0   Checksum: 0x46E4   Length: 24  Number of Links: 0  

Example 9-130 shows the configuration of R1, which shows that the primary and secondary address are included in different areas.

Example 9-130 R1's Primary and Secondary Address Configurations
 R1#  interface Ethernet0    ip address 131.108.3.1 255.255.255.0 secondary    ip address 131.108.2.1 255.255.255.0   !   router ospf 1   network 131.108.1.0 0.0.0.255 area 0   network 131.108.2.0 0.0.0.255 area 0   network 131.108.3.0 0.0.0.255 area 2  
Solution

To fix this problem, change the configuration on R1 so that the secondary address also belongs to area 0. Example 9-131 shows the configuration on R1, which shows that the secondary address is included in the area as the primary address.

Example 9-131 Configuring R1's Secondary Address to Be in the Same Area as the Primary Address
 R1#  interface Ethernet0    ip address 131.108.3.1 255.255.255.0 secondary    ip address 131.108.2.1 255.255.255.0   !   router ospf 1   network 131.108.1.0 0.0.0.255 area 0   network 131.108.2.0 0.0.0.255 area 0   network 131.108.3.0 0.0.0.255 area 0  

Example 9-132 shows the output of show ip route 131.108.3.0, which shows that after fixing this problem, the route came back in the routing table.

Example 9-132 Verifying That the 131.108.3.0 Route Is Being Advertised Again
 R2#  show ip route 131.108.3.0   Routing entry for 131.108.3.0/24   Known via "ospf 1", distance 110, metric 64, type intra area  Redistributing via ospf 1   Last update from 131.108.1.1 on Serial0, 04:22:21 ago   Routing Descriptor Blocks:   * 131.108.1.1, from 131.108.2.1, 04:22:21 ago, via Serial0       Route metric is 64, traffic share count is 1 R2# 
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Troubleshooting IP Routing Protocols
Troubleshooting IP Routing Protocols (CCIE Professional Development Series)
ISBN: 1587050196
EAN: 2147483647
Year: 2002
Pages: 260

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