Some Useful Commands to Troubleshoot IP Routing

To see some general routing information

#show ip route summary
IP routing table name is default (0x0)
IP routing table maximum-paths is 32
Route Source    Networks    Subnets     Replicates Overhead    Memory (bytes)
connected       0           13          0           1408        3744
static          0           0           0           0           0
application     0           0           0           0           0
ospf 100        0           6           0           768         1752
Intra-area: 6 Inter-area: 0 External-1: 0 External-2: 0
NSSA External-1: 0 NSSA External-2: 0
bgp 14234       103         1006        0           106464      319392
External: 629 Internal: 455 Local: 25

internal        63                                              111864

Total 166 1025 0 108640 436752

Shows how much memory is being consumed by each routing process.

To see information on OSPF Area Border Routers and Autonomous System Border Routers

#show ip ospf border-routers

OSPF Router with ID (10.0.0.2) (Process ID 100)

Base Topology (MTID 0)

Internal Router Routing Table
Codes: i - Intra-area route, I - Inter-area route

i 10.0.0.3 [10] via 10.0.23.2, Ethernet0/1, ABR/ASBR, Area 0, SPF 9
i 10.0.0.1 [10] via 10.0.12.1, Ethernet0/0, ASBR, Area 1, SPF 5
I 10.0.0.4 [20] via 10.0.23.2, Ethernet0/1, ASBR, Area 0, SPF 92

Basically shows how your router is intended to reach each of the ABRs and ASBRs it knows about.

To see which routing information is originated by your OSPF-enabled router

#show ip ospf database self-originate

OSPF Router with ID (10.0.0.2) (Process ID 100)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
10.0.0.2 10.0.0.2 156 0x80000006 0x005D69 1

Summary Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
10.0.12.0 10.0.0.2 111 0x80000001 0x006EA5

Summary ASB Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
10.0.0.1 10.0.0.2 111 0x80000001 0x00EC2E

Router Link States (Area 1)

Link ID ADV Router Age Seq# Checksum Link count
10.0.0.2 10.0.0.2 156 0x80000003 0x00746B 1

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.23.0       10.0.0.2        111         0x80000001 0x00F414
10.0.34.0       10.0.0.2        111         0x80000001 0x00DF14

Summary ASB Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.0.3        10.0.0.2        111         0x80000001 0x00D840
10.0.0.4        10.0.0.2        111         0x80000001 0x0033DA

The output above is taken from Router that is ABR, so you can see Summary (Type 3) LSAs that this router generates and sends to Area 1 to tell about the routes belonging to Area 0 and vice versa. Also you can see Summary ASB LSAs that it sends to inform routers in Area 0 about an ASBR it sees in Area 1 and routers in Area 1 about ASBRs in Area 1.

Don't Fragment

Network Engineer experience

Some Useful Commands to Troubleshoot IP Routing

To see some general routing information

To see information on OSPF Area Border Routers and Autonomous System Border Routers

To see which routing information is originated by your OSPF-enabled router

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