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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 :
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
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 131.108.3.0R2#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 AdvertisedOSPF 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
Debugs and VerificationExample 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 InterfaceR1# 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 131.108.3.0R1# 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 SolutionR1 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 131.108.3.0/24R1# 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 Database1# 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 AgainR2# 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 DownOSPF 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
Debugs and VerificationRecall 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 R1R1# 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 SolutionTo 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 InterfaceR1# 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 AgainR2# 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 InterfaceWhen 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
Figure 9-49 shows the flowchart to follow to solve this problem. Figure 9-49. Problem-Resolution Flowchart
Debugs and VerificationExample 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 InformationR1# 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 ConfigurationsR1# 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 SolutionTo 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 AddressR1# 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 AgainR2# 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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