# OSPF

> Markdown source of <https://docs.calebsargeant.com/networking/cisco/routing/ospf/>.

## Concepts and Planning

### Link State Routing Protocols

- Two types

  > - IS-IS
  > - OSPF

- Maintain three tables

  > - Neighbour table
  > - Topology table
  > - Routing table

- Use Dijkstra's Shortest Path First (SPF) algorithm

- Send triggered updates to announce network changes

- Send periodic updates (LS refresh) on long intervals

### OSPF Area Design and Terms

![ospf concepts and planning](_images/ospf-concepts-and-planning.png)

- All areas must connect to area 0
- All routers in an area have the same topology table
- Goal: localize updates within an area
- Requires a hierarchal design

### Understanding OSPF Neighbour Relationships

1.  Determine your own Router ID

> 1.  The Router ID is simply the router's name in the OSPF process
> 2.  Highest active interface IP address when OSPF starts (loopbacks beat physical interfaces)
> 3.  Dangerous to have a dynamic Router ID
> 4.  Can be hard-coded using the "router-id" command

1.  Add interfaces to the link state database (dictated by the network command)
2.  Send a hello message on chosen interface(s)

> 1.  **Down state**
> 2.  Sent once every 10 seconds on broadcast/p2p networks
> 3.  Sent once every 30 seconds on NMBA networks
> 4.  Contains all sorts of information (\* = neighbours must be same to form neighbor relationship)
>
> > 1.  Router ID
> > 2.  Hello and Dead Timers\*
> > 3.  Network Mask\*
> > 4.  Area ID\*
> > 5.  Neighbours
> > 6.  Router Priority
> > 7.  DR/BDR IP address
> > 8.  Authentication Password\*

1.  Receive Hello

> 1.  **Init State**
> 2.  Check hello/dead interval
> 3.  Check netmasks
> 4.  Check area ID
> 5.  Check authentication passwords

1.  Send Reply Hello

> 1.  **2-way State**
> 2.  Am I listed as a neighbour in your hello packet
> 3.  (if yes, reset dead timer)
> 4.  (if no, add as a new neighbour)

1.  Master-Slave Relationship Determined

> 1.  **Exstart State**
> 2.  Determined by "priority", router-id breaks the tie
> 3.  Master Sends Database Description (DBD) packet
>
> > 1.  DBD = cliff notes of link-state database
>
> 1.  Slave sends its DBD packets

1.  DBDs are acknowledged and reviewed

> 1.  **Loading state**
> 2.  Slave requests details (link-state requests - LSR)
> 3.  Master sends updates (link-state updates - LSU)
> 4.  Master requests details (LSR)
> 5.  Slave sends updates (LSU)

1.  Neighbours are synchronized

> 1.  **Full-state**
> 2.  Now it's time to run the Dijkstra SPF algorithm to figure out what to do with all this data

### OSPF's Cost

$$Cost = \frac{100}{BandwidthInMbps}$$

- 56K = 1785
- 64K = 1562
- T1 (1.544M) = 65
- E1 (2.048M) = 48
- Ethernet = 10
- Fast Ethernet = 1

### Understanding DR and BDR

- Designated Router = DR
- Backup DR = BDR
- DROTHER = client router
- Router send updates to DR on 224.0.0.6, DR sends updates to all its neighbours on 224.0.0.5.
- 1 DR and BDR for every shared segment
- No DR and BDR on point-to-point links (no point)

### DR and BDR Election

Elected via Router Priority (which is all 1 by default). The tie is broken by Router-ID. DR is only really important in NMBA networks, otherwise random DR and BDR is okay. All routers connected to DR will be in Full state. Other routers are in 2-way state (which is okay).

### OSPF Packet Types

- Hello

- Database Description (DBD)

- Link-State Request (LSR)
  - sent to master

- Link-State Advertisement (LSA)  
  - updates about individual routes

- Link-State Update (LSU)  
  - sent to slave

- Link-State Acknowledgment (LSACK)

## Basic Configuration

### Difference between E1 and E2

E1 = increment their metric (used if their is more than one way out the network - out of ASBR) E2 = do not increment their metric

### Basic OSPF Configuration

[ospf-basic-configuration.zip](https://raw.githubusercontent.com/CalebSargeant/docs/master/docs/networking/cisco/routing/_docs/ospf-basic-configuration.zip)

![ospf basic configuration](_images/ospf-basic-configuration.png)

**Router 1**

``` text
R1(config)#int g0/0
R1(config-if)#ip add 172.30.0.1 255.255.255.0
R1(config-if)#no shut
R1(config)#ip route 172.16.0.0 255.255.255.0 null0
R1(config)#ip route 172.16.1.0 255.255.255.0 null0
R1(config)#ip route 172.16.2.0 255.255.255.0 null0
R1(config)#ip route 172.16.3.0 255.255.255.0 null0
R1(config)#router ospf 1
R1(config-router)#net 172.30.0.1 0.0.0.0 area 0
R1(config-router)#router-id 1.1.1.1
R1(config-router)#redistribute static subnets metric 200 metric-type 2
R1(config-router)#summary-address 172.16.0.0 255.255.252.0
R1(config-router)#auto-cost reference-bandwidth 1000
R1(config-router)#do wr
```

**Router 2**

``` text
R2(config)#int g0/0
R2(config-if)#ip add 172.30.0.2 255.255.255.0
R2(config-if)#ip ospf priority 0
R2(config-if)#no shut
R2(config-if)#int s1/0
R2(config-if)#ip add 172.30.10.2 255.255.255.0
R2(config-if)#band 500
R2(config-if)#no shut
R2(config-if)#router ospf 1
R2(config-router)#network 172.30.0.2 0.0.0.0 area 0
R2(config-router)#router-id 2.2.2.2
R2(config-router)#network 172.30.10.2 0.0.0.0 area 10
R2(config-router)#area 10 range 10.10.0.0 255.255.252.0
R2(config-router)#auto-cost reference-bandwidth 1000
R2(config-router)#do wr
```

**Router 3**

``` text
R3(config)#int g0/0
R3(config-if)#ip add 172.30.0.3 255.255.255.0
R3(config-if)#ip ospf priority 0
R3(config-if)#no shut
R3(config-if)#int s1/0
R3(config-if)#ip add 172.30.20.3 255.255.255.0
R3(config-if)#band 500
R3(config-if)#no shut
R3(config)#router ospf 1
R3(config-router)#router-id 3.3.3.3
R3(config-router)#net 172.30.0.3 0.0.0.0 area 0
R3(config-router)#net 172.30.20.3 0.0.0.0 area 20
R3(config-router)#area 20 range 10.20.0.0 255.255.252.0
R3(config-router)#auto-cost reference-bandwidth 1000
R3(config-router)#do wr
```

**Router 4**

``` text
R4(config)#int s1/0
R4(config-if)#ip add 172.30.20.4 255.255.255.0
R4(config-if)#no shut
R4(config-if)#band 500
R4(config-if)#int lo1
R4(config-if)#ip add 10.20.0.1 255.255.255.0
R4(config-if)#int lo2
R4(config-if)#ip add 10.20.1.1 255.255.255.0
R4(config-if)#int lo3
R4(config-if)#ip add 10.20.1.1 255.255.255.0
R4(config-if)#ip add 10.20.2.1 255.255.255.0
R4(config-if)#int lo4
R4(config-if)#ip add 10.20.3.1 255.255.255.0
R4(config)#router ospf 1
R4(config-router)#router-id 4.4.4.4
R4(config-router)#network 10.0.0.0 0.255.255.255 area 20
R4(config-router)#network 172.30.20.4 0.0.0.0 area 20
R4(config-router)#auto-cost reference-bandwidth 1000
R4(config-router)#do wr
```

**Router 5**

``` text
R5(config)#int s1/0
R5(config-if)#ip add 172.30.10.5 255.255.255.0
R5(config-if)#band 500
R5(config-if)#no shut
R5(config-if)#int lo1
R5(config-if)#ip add 10.10.0.1 255.255.255.0
R5(config-if)#ip ospf network point-to-point
R5(config-if)#int lo2
R5(config-if)#ip add 10.10.1.1 255.255.255.0
R5(config-if)#int lo3
R5(config-if)#ip add 10.10.2.1 255.255.255.0
R5(config-if)#int lo4
R5(config-if)#ip add 10.10.3.1 255.255.255.0
R5(config)#router ospf 1
R5(config-router)#router-id 5.5.5.5
R5(config-router)#network 10.10.0.0 0.0.255.255 area 10
R5(config-router)#network 172.30.10.5 0.0.0.0 area 10
R5(config-router)#auto-cost reference-bandwidth 1000
R5#wr
```

## Advanced Configuration

### OSPF Network Types

- Broadcast, multi-access networks
  - Example: Ethernet, token ring
  - Single operation mode
  - DR/BDR election, 10 sec. hellos, DUAL multicast add.
- Point-to-Point networks
  - Example: T/ Cas, ISDN BRI/PRI
  - Single operation mode
  - No DR/BDR, 10 sec. hellos, single multicast add.
- Non-Broadcast Multi-access (NBMA) networks
  - Ex: Frame-relay, ATM
  - Five modes of operation
    - Non-broadcast (NBMA) - RFC standard
    - Point-to-Point - RFC standard
    - Point-to-Point - CISCO proprietary
    - Broadcast - CISCO proprietary
    - Point-to-Multipoint, non-broadcast - CISCO proprietary

### Non-Broadcast Mode

- Default mode for x.25, FR, ATM
- Neighbours statically configured
- Must be one subnet
- Acts like a LAN environment
- DR/BDR elected (must have full connectivity!)

### Point-to-Multipoint Mode

- Fixes issues with NMBA
- Requires single subnet
- No DR/BDR elected
- Neighbours automatically form (must be able to send pseudo-broadcasts sent over 224.0.0.5)

### Point-to-Point Mode

- Uses separate sup-interfaces
- Requires different subnets
- No DR/BDR elected
- Neighbours automatically form

### OSPF Advanced Configuration

[ospf-advanced-configuration.zip](https://raw.githubusercontent.com/CalebSargeant/docs/master/docs/networking/cisco/routing/_docs/ospf-advanced-configuration.zip)

![ospf advanced configuration](_images/ospf-advanced-configuration.png)

**Router 1**

``` text
R1(config-router)#int lo0
R1(config-if)#ip add 1.1.1.1 255.255.255.0
R1(config-if)#ip ospf network point-to-point
R1(config)#int s1/0
R1(config-if)#encap frame-relay
R1(config-if)#no shut
R1(config-if)#int s1/0.1
R1(config-if)#int s1/0.1 multi
R1(config-subif)#ip add 10.12.3.1 255.255.255.0
R1(config-subif)#frame-relay map ip 10.12.3.2 102
R1(config-subif)#frame-relay map ip 10.12.3.3 103
R1(config)#router ospf 1
R1(config-router)#network 10.12.3.0 0.0.0.255 area 0
R1(config-router)#network 1.1.1.1 0.0.0.0 area 0
R1(config-router)#neighbor 10.12.3.2 pri 0
R1(config-router)#neighbor 10.12.3.3 pri 0
R1(config-router)#router-id 1.1.1.1
R1(config-router)#do wr
```

**Router 2**

``` text
R2(config)#int lo1
R2(config-if)#ip add 2.2.2.2 255.255.255.0
R2(config)#int s1/0
R2(config-if)#encap frame-relay
R2(config-if)#no shut
R2(config)#int s1/0.1 multi
R2(config-subif)#ip add 10.12.3.2 255.255.255.0
R2(config-subif)#frame-relay interface-dlci 201
R2(config-subif)#ip ospf priority 0
R2(config)#int s1/1
R2(config-if)#encap frame-relay
R2(config-if)#no shut
R2(config)#int s1/1.1 point-to-point
R2(config-subif)#ip add 10.24.0.2 255.255.255.0
R2(config-subif)#frame-relay interface-dlci 204
R2(config)#router ospf 1
R2(config-router)#network 10.12.3.0 0.0.0.255 area 0
R2(config-router)#network 10.24.0.2 0.0.0.0 area 24
R2(config-router)#network 2.2.2.2 0.0.0.0 area 0
R2(config-router)#router-id 2.2.2.2
R2(config-if)#do wr
```

**Router 3**

``` text
R3(config-if)#int lo0
R3(config-if)#ip add 3.3.3.3 255.255.255.0
R3(config)#int s1/0
R3(config-if)#encap frame-relay
R3(config-if)#no shut
R3(config)#int s1/0.1 multi
R3(config-subif)#ip add 10.12.3.3 255.255.255.0
R3(config-subif)#frame-relay interface-dlci 301
R3(config-subif)#ip ospf pri 0
R3(config-subif)#router ospf 1
R3(config-router)#router-id 3.3.3.3
R3(config-router)#network 10.12.3.0 0.0.0.255 area 0
R3(config-router)#network 10.35.6.3 0.0.0.0 area 356
R3(config-router)#network 3.3.3.3 0.0.0.0 area 0
R3(config)#int s1/1
R3(config-if)#encap frame-relay
R3(config-if)#no shut
R3(config)#int s1/1.1 multi
R3(config-subif)#ip add 10.35.6.3 255.255.255.0
R3(config-subif)#frame-relay map ip 10.35.6.5 305
R3(config-subif)#frame-relay map ip 10.35.6.6 306
R3(config-subif)#ip ospf hello-interval 30
R3(config)#int s1/1
R3(config-if)#do wr
```

**Router 4**

``` text
R4(config)#int s1/0
R4(config-if)#encap frame-relay
R4(config-if)#no shut
R4(config-if)#int s1/0
R4(config)#int s1/0.1 point-to-point
R4(config-subif)#ip add 10.24.0.4 255.255.255.0
R4(config-subif)#frame-relay interface-dlci 402
R4(config-fr-dlci)#int lo1
R4(config)#int lo0
R4(config-if)#ip add 4.4.4.4 255.255.255.0
R4(config)#router ospf 1
R4(config-router)#router-id 4.4.4.4
R4(config-router)#network 10.24.0.0 0.0.0.255 area 24
R4(config-router)#network 4.4.4.4 0.0.0.0 area 24
R4(config-router)#int lo0
R4(config)#int s1/0
R4(config-if)#encap frame-relay
R4(config-if)#no shut
R4(config)#int s1/0.1 point-to-point
R4(config-subif)#ip add 10.24.0.4 255.255.255.0
R4(config-subif)#frame-relay interface-dlci 402
```

**Router 5**

``` text
R5(config)#int s1/0
R5(config-if)#encap frame-relay
R5(config-if)#no shut
R5(config)#int s1/0.1 multipoint
R5(config-subif)#ip ospf hello-interval 10
R5(config-subif)#ip add 10.35.6.5 255.255.255.0
R5(config-subif)#frame-relay interface-dlci 503
R5(config-subif)#router ospf 1
R5(config-router)#router-id 5.5.5.5
R5(config-router)#net 5.5.5.5 0.0.0.0 area 356
R5(config-router)#net 10.35.6.0 0.0.0.255 area 356
R5(config)#int lo0
R5(config-if)#ip add 5.5.5.5 255.255.255.0
R5(config)#do wr
```

**Router 6**

``` text
Router 6
R6(config)#int s1/0
R6(config-if)#encap frame-relay
R6(config-if)#no shut
R6(config-if)#int s1/0.1 multi
R6(config-subif)#ip ospf hello-interval 10
R6(config-subif)#frame-relay interface-dlci 603
R6(config-fr-dlci)#ip add 10.35.6.6 255.255.255.0
R6(config)#int lo0
R6(config-if)#ip add 6.6.6.6 255.255.255.0
R6(config)#router ospf 1
R6(config-router)#router-id 6.6.6.6
R6(config-router)#net 10.35.6.6 0.0.0.0 area 356
R6(config-router)#net 6.6.6.6 0.0.0.0 area 356
R6(config)#do wr
```

**Frame Relay Switch 1**

``` text
FRS1(config)#frame-relay switch
FRS1(config)#int s1/0
FRS1(config-if)#encap frame-relay
FRS1(config-if)#frame-relay intf-type dce
FRS1(config-if)#frame-relay route 102 int s1/1 201
FRS1(config-if)#frame-relay route 103 int s1/2 301
FRS1(config-if)#no shut
FRS1(config-if)#int s1/1
FRS1(config-if)#encap frame-relay
FRS1(config-if)#frame-relay intf-type dce
FRS1(config-if)#frame-relay route 201 int s1/0 102
FRS1(config-if)#no shut
FRS1(config-if)#int s1/2
FRS1(config-if)#encap frame-relay
FRS1(config-if)#frame-relay intf-type dce
FRS1(config-if)#frame-relay route 301 int s1/0 103
FRS1(config-if)#no shut
FRS1(config-if)#do wr
```

**Frame Relay Switch 2**

``` text
FRS2(config)#int s1/0
FRS2(config)#frame-relay switch
FRS2(config)#int s1/0
FRS2(config-if)#encap frame-relay
FRS2(config-if)#frame-relay intf-type dce
FRS2(config-if)#frame-relay route 204 int s1/1 402
FRS2(config-if)#no shut
FRS2(config-if)#int s1/1
FRS2(config-if)#encap frame-relay
FRS2(config-if)#frame-relay route 402 int s1/0 204
FRS2(config-if)#frame-relay intf-type dce
FRS2(config-if)#no shut
FRS2(config-if)#do wr
```

**Frame Relay Switch 3**

``` text
FRS3(config)#frame-relay switch
FRS3(config)#int s1/0
FRS3(config-if)#encap frame-rela
FRS3(config-if)#frame-relay intf-type dce
FRS3(config-if)#frame-relay route 305 int s1/1 503
FRS3(config-if)#frame-relay route 306 int s1/2 603
FRS3(config-if)#no shut
FRS3(config-if)#int s1/2
FRS3(config-if)#encap frame-relay
FRS3(config-if)#frame-relay route 603 int s1/0 306
FRS3(config-if)#frame-relay intf-type dce
FRS3(config-if)#no shut
FRS3(config)#int s1/1
FRS3(config-if)#encap frame
FRS3(config-if)#encap frame-relay
FRS3(config-if)#frame-relay intf-type dce
FRS3(config-if)#frame-relay route 503 int s1/0 305
FRS3(config-if)#no shut
FRS3(config-if)#do wr
```

## OSPF Area Types and Options

### OSPF Areas and Router Types

Link state advertisements (LSAS) are the building blocks of OSPF; many types exist

- LSA type 1: router LSA
- LSA type 2: network LSA (DR generated)
- LSA type 3: summary LSA (ABR summary route)
- LSA type 4: summary LSA (ASBR location)
- LSA type 5: external LSA (ASBR summary route)

### Virtual Links

[ospf-virtual-links.zip](https://raw.githubusercontent.com/CalebSargeant/docs/master/docs/networking/cisco/routing/_docs/ospf-virtual-links.zip)

![ospf virtual links](_images/ospf-virtual-links.png)

**Router 1**

``` text
R1(config)#int s1/0
R1(config-if)#ip add 10.2.0.2 255.255.255.0
R1(config-if)#no shut
R1(config-if)#router ospf 1
R1(config-router)#net 10.2.0.0 0.0.0.255 area 2
R1(config-router)#router-id 1.1.1.1
R1(config-router)#do wr
```

**Router 2**

``` text
R2(config)#router ospf 1
R2(config-router)#router-id 2.2.2.2
R2(config)#int s1/0
R2(config-if)#ip add 10.1.0.2 255.255.255.0
R2(config-if)#router ospf 1
R2(config-router)#net 10.1.0.0 0.0.0.255 area 1
R2(config-router)#area 1 virtual-link 3.3.3.3
R2(config-router)#int s1/0
R2(config-if)#no shut
R2(config-if)#int s1/1
R2(config-if)#ip add 10.2.0.1 255.255.255.0
R2(config-if)#no shut
```

**Router 3**

``` text
R3(config)#int s1/0
R3(config-if)#ip add 10.0.0.2 255.255.255.0
R3(config-if)#no shut
R3(config-if)#int s1/1
R3(config-if)#ip add 10.1.0.1 255.255.255.0
R3(config-if)#no shut
R3(config-if)#router ospf 1
R3(config-router)#router-id 3.3.3.3
R3(config-router)#network 10.0.0.0 0.0.0.255
R3(config-router)#network 10.0.0.0 0.0.0.255 area 0
R3(config-router)#network 10.1.0.0 0.0.0.255 area 1
R3(config-router)#int s1/1
R3(config)#router ospf 1
R3(config-router)#area 1 virtual-link 2.2.2.2
```

**Router 4**

``` text
R4(config)#int s1/0
R4(config-if)#ip add 10.0.0.1 255.255.255.0
R4(config-if)#no shut
R4(config-if)#router ospf 1
R4(config-router)#router-id 4.4.4.4
R4(config-router)#network 10.0.0.0 0.0.0.255 area 0
R4(config-if)#do wr
```

### Stub and Totally Stubby Areas

- Stubby Area: blocks type 5 LSA from entering
- Totally stubby Area: blocks type 3, 4, and 5 LSAs from entering (CISCO proprietary)
- Not-So Stubby Area (NSSA): passes external routes through via type 7  LSAs; these convert back to type 5 once they reach the backbone

[ospf-stub-and-totally-stubby-areas.zip](https://raw.githubusercontent.com/CalebSargeant/docs/master/docs/networking/cisco/routing/_docs/ospf-stub-and-totally-stubby-areas.zip)

![ospf stub and totally stubby areas](_images/ospf-stub-and-totally-stubby-areas.png)

**Router 1**

``` text
R1(config)#int s1/0
R1(config-if)#ip add 10.10.2.2 255.255.255.0
R1(config-if)#no shut
R1(config-if)#router ospf 1
R1(config-router)#router-id 1.1.1.1
R1(config-router)#net 10.10.2.0 0.0.0.255
R1(config-router)#net 10.10.2.0 0.0.0.255 area 2
R1(config-router)#area 2 stub
R1#wr
```

**Router 2**

``` text
R2(config)#int s1/1
R2(config-if)#ip add 10.10.2.1 255.255.255.0
R2(config-if)#no shut
R2(config-if)#int s1/0
R2(config-if)#ip add 10.10.0.3 255.255.255.0
R2(config-if)#no shut
R2(config-if)#router ospf 1
R2(config-router)#router-id 2.2.2.2
R2(config-router)#net 10.10.2.0 0.0.0.255 area 2
R2(config-router)#net 10.10.0.0 0.0.0.255 area 0
R2(config-router)#do wr
```

**Router 4**

``` text
R4(config)#int s1/0
R4(config-if)#ip add 10.10.0.4 255.255.255.0
R4(config-if)#no shut
R4(config-if)#int s1/1
R4(config-if)#ip ad 10.10.1.1 255.255.255.0
R4(config-if)#no shut
R4(config-if)#router ospf 1
R4(config-router)#router-id 4.4.4.4
R4(config-router)#net 10.10.0.0 0.0.0.255 area 0
R4(config-router)#net 10.10.1.0 0.0.0.255 area 1
R4(config-router)#area 1 stub no-summary
R4(config-router)#do wr
```

**Router 5**

``` text
R5(config)#int s1/0
R5(config-if)#ip add 10.10.1.2 255.255.255.0
R5(config-if)#no shut
R5(config-if)#router ospf 1
R5(config-router)#router-id 5.5.5.5
R5(config-router)#net 10.10.1.0 0.0.0.255 area 1
R5(config-router)#area 1 stub
R5(config-router)#area 1 nssa
R5#wr
```

### OSPF Special Areas

[ospf-stub-lab.zip](https://raw.githubusercontent.com/CalebSargeant/docs/master/docs/networking/cisco/routing/_docs/ospf-stub-lab.zip)

![ospf stub lab](_images/ospf-stub-lab.png)

**Router 1**

``` text
R1(config)#int g0/0
R1(config-if)#ip add 10.100.1.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#router ospf 1
R1(config-router)#net 10.100.1.0 0.0.0.255 area 0
R1(config-router)#router-id 1.1.1.1
R1(config)#ip route 172.31.0.0 255.255.255.0 null0
R1(config)#ip route 172.31.1.0 255.255.255.0 null0
R1(config)#ip route 172.31.2.0 255.255.255.0 null0
R1(config)#ip route 172.31.3.0 255.255.255.0 null0
R1(config-router)#redistribute static subnets metric-type 1 metric 50
R1(config-router)#passive-interface default
R1(config-router)#no passive-interface g0/0
R1(config-router)#int g0/0
R1(config-if)#ip ospf authentication message-digest
R1(config-if)#ip ospf message-digest-key 1 md5 cisco
```

**Router 2**

``` text
R2(config)#int g0/0
R2(config-if)#ip add 10.100.1.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#int s1/0
R2(config-if)#ip add 10.23.1.0 255.255.255.0
Bad mask /24 for address 10.23.1.0
R2(config-if)#ip add 10.23.1.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#router ospf 1
R2(config-router)#router-id 2.2.2.2
R2(config-router)#net 10.100.1.0 0.0.0.255 area 0
R2(config-router)#net 10.23.1.0 0.0.0.255 area 23
R2(config-router)#passive-interface default
R2(config-router)#no passive-interface g0/0
R2(config-router)#no passive-interface s1/0
R2(config-router)#area 23 stub no-summary
R2(config-router)#int g0/0
R2(config-if)#ip ospf authentication message-digest
R2(config-if)#ip ospf message-digest-key 1 md5 cisco
R2(config-if)#ip ospf authentication-key cisco
```

**Router 3**

``` text
R3(config)#int s1/0
R3(config-if)#ip add 10.23.1.0 255.255.255.0
Bad mask /24 for address 10.23.1.0
R3(config-if)#no shut
R3(config-if)#int lo0
R3(config-if)#ip add 172.30.0.1 255.255.255.0
R3(config-if)#int lo1
R3(config-if)#ip add 172.30.1.1 255.255.255.0
R3(config-if)#int lo2
R3(config-if)#ip add 172.30.1.1 255.255.255.0
R3(config-if)#ip add 172.30.2.1 255.255.255.0
R3(config-if)#int lo3
R3(config-if)#ip add 172.30.3.1 255.255.255.0
R3(config-if)#router ospf 1
R3(config-router)#net 172.30.0.0 0.0.3.255 area 23
R3(config-router)#passive-interface default
R3(config-router)#no passive-interface s1/0
R3(config-router)#area 23 stub
R3(config-router)#int s1/0
R3(config-if)#ip ospf authentication-key cisco
```

**Router 4**

``` text
R4(config)#int g0/0
R4(config-if)#ip add 10.100.1.4 255.255.255.0
R4(config-if)#no shut
R4(config-if)#int s1/0
R4(config-if)#ip add 10.45.1.4 255.255.255.0
R4(config-if)#no shut
R4(config-if)#router ospf 1
R4(config-router)#router-id 4.4.4.4
R4(config-router)#net 10.100.1.0 0.0.0.255 area 0
R4(config-router)#net 10.45.1.0 0.0.0.255 area 45
R4(config-router)#net 10.45.1.0 0.0.0.255 area 45
R4(config-router)#passive-interface default
R4(config-router)#no passive-interface g0/0
R4(config-router)#no passive-interface s1/0
R4(config-router)#int g0/0
R4(config-if)#ip ospf authentication message-digest
R4(config-if)#ip ospf message-digest-key 1 md5 cisco
R4(config-if)#router ospf 1
R4(config-router)#area 45 stub
```

**Router 5**

``` text
R5(config)#int s1/0
R5(config-if)#ip add 10.45.1.5 255.255.255.0
R5(config-if)#no shut
R5(config-if)#router ospf 1
R5(config-router)#router-id 5.5.5.5
R5(config-router)#net 10.45.1.0 0.0.0.255 area 45
R5(config-router)#passive-interface default
R5(config-router)#no passive-interface s1/0
R5(config-router)#area 45 stub
```

**Router 6**

``` text
R6(config)#int g0/0
R6(config-if)#ip add 10.100.1.6 255.255.255.0
R6(config-if)#no shut
R6(config-if)#int s1/0
R6(config-if)#ip add 10.67.1.6 255.255.255.0
R6(config-if)#no shut
R6(config-if)#router ospf 1
R6(config-router)#router-id 6.6.6.6
R6(config-router)#net 10.100.1.0 0.0.0.255 area 0
R6(config-router)#net 10.67.1.0 0.0.0.255 area 67
R6(config-router)#passive-interface default
R6(config-router)#no passive-interface g0/0
R6(config-router)#no passive-interface s1/0
R6(config-router)#area 67 virtual-link 7.7.7.7
R6(config-router)#int g0/0
R6(config-if)#ip ospf authentication message-digest
R6(config-if)#ip ospf message-digest-key 1 md5 cisco
```

**Router 7**

``` text
R7(config)#int s1/0
R7(config-if)#ip add 10.67.1.7 255.255.255.0
R7(config-if)#no shut
R7(config-if)#router ospf 1
R7(config-router)#router-id 7.7.7.7
R7(config-router)#net 10.67.1.0 0.0.0.255 area 67
R7(config-router)#int s1/1
R7(config-if)#ip add 10.78.1.7 255.255.255.0
R7(config-if)#no shut
R7(config-if)#router ospf 1
R7(config-router)#net 10.78.1.0 0.0.0.255 area 78
R7(config-router)#passive-interface default
R7(config-router)#no passive-interface s1/0
R7(config-router)#no passive-interface s1/1
R7(config-router)#area 67 virtual-link 6.6.6.6
```

**Router 8**

``` text
R8(config)#int s1/0
R8(config-if)#ip add 10.78.1.8 255.255.255.0
R8(config-if)#no shut
R8(config-if)#router ospf 1
R8(config-router)#router-id 8.8.8.8
R8(config-router)#net 10.78.1.0 0.0.0.255 area 78
R8(config-router)#passive-interface default
R8(config-router)#no passive-interface s1/0
```