LAB ASSIGNMENTS

OSPF

Sample Assignments


Implement OSPF

Objective:

Configure OSPF area 0 and Area 1 as per IGP diagram and the following requirements

  • The OSPF process ID must be 100 for all OSPF Routers
  • OSPF router-id must be stable and must be configured using the IP address of interface Loopback 0
  • Loopback 0 interfaces should be advertised in the OSPF area as shown in the IGP topology diagram OR mentioned below and must appear as /32 host routes
  • Network 100.100.100.0/24 (F0/1 Interface) should be advertised in the OSPF 500, but no OSPF hello may be sent out of this interface.
  • Ensure that R2 is elected as the Designated Router on to interfaces Fast Ethernet 0/0 and fast Ethernet 0/1 and maintains the best chance of being re-elected as such.
  • OSPF Area 1 must be configured as a stub area , which allows the injection of external routes
  • Do not create OSPF additional areas
  • Ensure that R2 originates a default route everywhere into the OSPF domain.


Directions:

Configure Loopback addresses on all routers with /32 mask

R1 Loopback Address = 1.1.1.1/32
R2 loopback address = 2.2.2.2/32
R3 Loopback Address = 3.3.3.3/32
R4 Loopback Address = 4.4.4.4/32
R5 Loopback address = 5.5.5.5/32

Configure IP addresses of Major Network 172.16.0.0/16 on physical Interfaces:

172.16. xy.z/24, Where x= Router Number (lowest Value)
Y= Router Number (Highest Value) ,XY= Subnet Number
Z= Router Number, z= Host ID

R1 , F0/0 Interface IP Address = 172.16.12.1/24 , AREA 0
R1, F0/1 Interface IP Address = 100.100.100.1/24 , AREA 500
R2, F0/0 Interface IP Address = 172.16.12.2/24, AREA 0
R2, S1/0 Interface IP Address = 172.16.24.2/24, AREA 1
R2, F0/1 Interface IP Address = 172.16.23.2/24, AREA 1
R3, F0/0 Interface IP Address = 172.16.23.3/24, AREA 1
R3, F0/1 Interface IP Address = 172.16.35.3/24, AREA 1
R4, F0/0 Interface IP Address = 172.16.45.4/24, AREA 1
R4, S1/0 Interface IP Address = 172.16.24.4/24, AREA 1
R5, F0/0 Interface IP Address = 172.16.35.5/24, AREA 1
R5, F0/1 Interface IP Address = 172.16.45.5/24, AREA 1

Advertise Loopback Addresses in Following OSPF Areas:

R1, Loopback Address = OSPF AREA 0
R2, Loopback Address = OSPF AREA 1
R3, Loopback Address = OSPF AREA 1
R4, Loopback Address = OSPF AREA 2
R5, Loopback Address = OSPF AREA 0

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OSPF Multiple Areas

Implement IPV4 OSPF:

Objective:

Configure OSPF area 0, 1, 2 as per IGP topology diagram and the following requirements:

  • The OSPF process ID can be any number
  • OSPF router-id must be stable and must be configured using the IP address of interface Loopback 0
  • Loopback 0 interfaces should be advertised in the OSPF area as shown in the IGP topology diagram and must appear as /32 host routes
  • Updates should be advertised only out of the interfaces that indicated in the IGP topology diagram
  • Ensure that R4 can still reach all OSPF networks via R3 in case R1 or R5 goes down
  • Do not create additional OSPF areas
  • Do not use any IP address not listed in diagram


Directions:

Configure Loopback addresses on all routers with /32 mask

R1 Loopback Address = 1.1.1.1/32
R2 loopback address = 2.2.2.2/32
R3 Loopback Address = 3.3.3.3/32
R4 Loopback Address = 4.4.4.4/32
R5 Loopback address = 5.5.5.5/32
R6 Loopback Address = 6.6.6.6/32
R7 Loopback Address = 7.7.7.7/32

ConfigureIP addresses of Major Network 172.16.0.0/16 on physical Interfaces

172.16. xy.z/24, Where x= Router Number (lowest Value)
Y= Router Number (Highest Value) ,XY= Subnet Number
Z= Router Number, z= Host ID

R1 , F0/0 Interface IP Address = 172.16.17.1/24 , AREA 0
R1, S1/1 Interface IP Address = 172.16.15.1/24 , AREA 0
R1, S1/0 Interface IP Address = 172.16.12.1/24, AREA 1
R2, S1/0 Interface IP Address = 172.16.12.2/24, AREA 1
R2, S1/1 Interface IP Address = 172.16.23.2/24, AREA 1
R3, S1/1 Interface IP Address = 172.16.23.3/24, AREA 1
R3, S1/0 Interface IP Address = 172.16.35.3/24, AREA 1
R3, F0/0 Interface IP Address = 172.16.34.3/24, AREA 2
R4, F0/1 Interface IP Address = 172.16.34.4/24, AREA 2
R5, S1/1 Interface IP Address = 172.16.35.5/24, AREA 1
R5, S1/0 Interface IP Address = 172.16.15.5/24, AREA 0
R5, F0/0 Interface IP Address = 172.16.56.5/24, AREA 0
R6, F0/0 Interface IP Address = 172.16.56.6/24 , AREA 0
R6, F0/1 Interface IP Address = 172.16.67.6/24, AREA 0
R7, F0/1 Interface IP Address = 172.16.67.7/24, AREA 0
R7, F0/0 Interface IP Address = 172.16.17.7/24, AREA 0

Advertise Loopback Addresses in Following OSPF Areas:

R1, Loopback Address = OSPF AREA 0
R2, Loopback Address = OSPF AREA 1
R3, Loopback Address = OSPF AREA 1
R4, Loopback Address = OSPF AREA 2
R5, Loopback Address = OSPF AREA 0
R6, Loopback Address = OSPF AREA 0
R7, Loopback Address = OSPF AREA 0

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OSPF Network Command

Understanding the OSPF Network Statement:

Objective:

Enable OSPF on R1 with the following area assignments using exactly four network statements

  • Interface 10.10.10.10 should be assigned to area 0
  • Interfaces 10.10.10.0 - 10.10.10.255 should be assigned to area 1
  • Interface 10.10.0.0 - 10.10.15.255 should be assigned to area 2
  • All other interfaces (1.0.0.0 - 223.255.255.255) should be assigned to area 3


Directions:

  • Create interface loopback0 on R1 with the IP address 10.10.10.10/32
  • Create interface loopback1 on R1 with the IP address 10.10.10.1/32
  • Create interface loopback2 on R1 with the IP address 10.10.10.255/32
  • Create interface loopback3 on R1 with the IP address 10.10.0.0/32
  • Create interface loopback4 on R1 with the IP address 10.10.15.255/32
  • Create interface loopback5 on R1 with the IP address 10.9.255.255/32
  • Create interface loopback6 on R1 with the IP address 10.10.16.0/32
  • Create interface loopback7 on R1 with the IP address 1.0.0.0/32
  • Create interface loopback8 on R1 with the IP address 223.255.255.255/32
  • Enable OSPF using a process-id of 1
  • Configure a network statement so that the interface 10.10.10.10 is in OSPF area 0
  • Configure a network statement so that interfaces in the range of 10.10.10.0 - 10.10.10.255 are in OSPF area 1
  • Configure a network statement so that interfaces in the range of 10.10.0.0 - 10.10.15.255 are in OSPF area 2
  • Configure a network statement so that interfaces in the range of 1.0.0.0 - 223.255.255.255 are in OSPF area 3

Ask Yourself

  • How does the wildcard mask relate to the subnet mask of the interface?
  • What happens if multiple OSPF network statements overlap?
  • How can I verify which area an interface belongs to?

Verification

  • R1#show ip ospf interface | include (Loopback[0-8]|Area)
  • Loopback0 is up, line protocol is up
  • Internet Address 10.10.10.10/32, Area 0
  • Loopback2 is up, line protocol is up
  • Internet Address 10.10.10.255/32, Area 1
  • Loopback1 is up, line protocol is up
  • Internet Address 10.10.10.1/32, Area 1
  • Loopback4 is up, line protocol is up
  • Internet Address 10.10.15.255/32, Area 2
  • Loopback3 is up, line protocol is up
  • Internet Address 10.10.0.0/32, Area 2
  • Loopback8 is up, line protocol is up
  • Internet Address 223.255.255.255/32, Area 3
  • Loopback7 is up, line protocol is up
  • Internet Address 1.0.0.0/32, Area 3
  • Loopback6 is up, line protocol is up
  • Internet Address 10.10.16.0/32, Area 3
  • Loopback5 is up, line protocol is up
  • Internet Address 10.9.255.255/32, Area 3

Breakdown

The first step in configuring OSPF is to enable the routing process globally. This is accomplished by issuing the router ospf command, followed by a locally significant process-id in global configuration mode. Once the process has been enabled, the next step in configuring OSPF is to enable the process on an interface by issuing the network statement.

Like EIGRP, the OSPF network statement uses a wildcard mask to identify whichinterface or interfaces are running the protocol. In addition to this, the network statement determines which link state area an interface will belong to. The wildcard mask option of the network statement works like the wildcard mask option of an IP access list, where a binary zero indicates to check the particular bit position, while a binary one indicates to ignore the particular bit position.

Usage of the wildcard mask in the network statement does not relate to the IP subnet mask of an interface or it's corresponding advertisement, but is simply used to determine which interface or interfaces belong to the area.

This is demonstrated in the above example through an exercise in binary logic. The most specific match for an interface in the OSPF network statement uses a wildcard mask of all zeros. The statement network 10.10.10.10 0.0.0.0 area 0 dictates that only the interface with the IP address 10.10.10.10 belongs to area 0. The next statement, network 10.10.10.0 0.0.0.255 area 1, dictates that any interface with an IP address of 10.10.10.X, where X is any number, belongs to area 1. Next, the statement network 10.10.0.0 0.0.15.255 area 2 dictates that any interface with an IP address of 10.10.X.Y, where X is a number from 0-15 and Y is any number, belongs to area 2. Lastly, all other interfaces that aren't already assigned to an area are assigned to area 3 with the statement network 0.0.0.0 255.255.255.255 area 3.

When multiple OSPF network statement are configured with overlapping matches, as in the above case, the most specific network statement determines which area the interface will exist in. For example the above statement network 0.0.0.0 255.255.255.255 area 3 dictates that all interfaces will participate in area 3. However, the more specific statement network 10.10.10.10 0.0.0.0 area 0 dictates that this particular interface will belong to area 0. To verify what area an interface is running in, issue the show ip ospf interface command in privilege level mode.

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Understand DR BDR in OSPF

OSPF DR/BDR Election

Objective: Configure OSPF on the Ethernet network between R1, R2 and R3 so That R1 is elected the DR, R2 is elected the BDR, and R3 does not Participate in the election.



Directions

  • Configure R1's interface f0/0 with the IP address 172.16.123.1/24
  • Configure R2's interface f0/0 with the IP address 172.16.123.2/24
  • Configure R3's interface f0/0 with the IP address 172.16.123.3/24
  • Configure R1's interface f0/0 with an OSPF priority of 100
  • Configure R2's interface f0/0 with an OSPF priority of 50
  • Configure R3's interface f0/0 with an OSPF priority of 0
  • Configure these interfaces in OSPF area 0
Ask Yourself

  • What is the default OSPF network type on an Ethernet segment?
  • Does this network type have a DR/BDR election?
  • What is the role of the DR?
  • What is the role of the BDR?
  • How does the DR/BDR election occur?
  • How can the DR/BDR election be influenced?
  • What happens when a router with a higher priority than the DR or BDR is Added to the segment?

Verification

R1#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.16.123.2 50 FULL/BDR 00:00:34 172.16.123.2 FastEthernet0/0
172.16.123.3 0 FULL/DROTHER 00:00:37 172.16.123.3 FastEthernet0/0

R2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.16.123.1 100 FULL/DR 00:00:36 172.16.123.1 FastEthernet0/0
172.16.123.3 0 FULL/DROTHER 00:00:34 172.16.123.3 FastEthernet0/0

R3#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
172.16.123.1 100 FULL/DR 00:00:37 172.16.123.1 FastEthernet0/0
172.16.123.2 50 FULL/BDR 00:00:31 172.16.123.2


R1#show ip ospf interface f0/0
FastEthernet0/0 is up, line protocol is up
Internet Address 172.16.123.1/24, Area 0
Process ID 1, Router ID 172.16.123.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 100
Designated Router (ID) 172.16.123.1, Interface address 172.16.123.1
Backup Designated router (ID) 172.16.123.2, Interface address 172.16.123.2


Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:05
Supports Link-local Signaling (LLS)
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 4 msec, maximum is 4 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 172.16.123.2 (Backup Designated Router)
Adjacent with neighbor 172.16.123.3
Suppress hello for 0 neighbor(s)

Breakdown

The OSPF Designated Router (DR) and Backup Designated Router (BDR) are roles assigned to devices on the OSPF network type broadcast and nonbroadcast in order to reduce LSA replication on the segment. When a device on the segment wants to send an LSA into the network, the LSA is sent to DR. The DR is then responsible for sending this LSA back out to all other devices on the segment. The BDR is used to take the place of the DR in the case of a network failure. Determination of which devices will be the DR and BDR on the segment is based on an election process.


This election process is decided by two values, the interface priority and the router-id. The interface priority is a number in the range of 0 to 255, with the default being 1 on all interfaces. An OSPF priority of 0 indicates that a device will not participate in the DR/BDR election, while a priority of 255 indicates that the device is most likely to be elected DR. If there is a tie in the OSPF priority, the device with the highest router-id is elected.

OSPF router-id can either be automatically selected or manually configured. For automatic selection the router will choose the highest loopback IP address on the router, or if there are no loopback address, the highest IP address assigned to any other interface. When the router-id is left up to automatic selection it can change if a new interface with a higher IP address is assigned to the router and the OSPF process is restarted. As the router-id must be unique to the entire OSPF domain, it is recommended that it be manually defined with the router-id command under the OSPF process.

One of the problems that can occur with the OSPF DR/BDR election relates to the speed at which the OSPF process loads. The OSPF DR/BDR election, unlike the IS-IS DIS election, does not support preemption. This means is that once the DR and BDR for a segment are determined, a new election cannot occur even if a new device with a higher priority or router-id comes on to the segment. Instead, a new election only occurs if the DR or BDR fails. If the DR fails, the BDR assumes the role of the DR, and a new election occurs for the BDR. If the BDR fails, a new election occurs for the BDR.

In the above example the implication of this can be seen if R1 comes on to the segment after R2 and R3 have performed the election. Even though R2's priority is lower than R1, R1 cannot preempt R2's DR status if it has already been elected. Therefore the only way to ensure that a particular device is elected the DR in all circumstances is to remove the other routers from the election by setting the OSPF priority to 0. This setup is common in cases where only one device has full layer 2 connectivity to all devices on the segment, such as the hub in a hub-and-spoke NBMA topology, in which case a failure of the hub would cause a loss of physical reachability between all other devices on the network. In such a case it is required to set the spoke devices to have a priority of 0, as the hub is the only device on the segment that can properly perform the duties of the DR. Once the OSPF election has occurred, issue the show ip ospf neighbor and show ip ospf interface commands to verify who have been elected the DR and BDR.

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