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Single-Area OSPFv2 Configuration, image - Coggle Diagram
Single-Area OSPFv2 Configuration
OSPF
OFPS Reference topology
The routers in the topology have a starting configuration, including interface addresses. There is currently no static routing or dynamic routing configured on any of the routers. All interfaces on R1, R2, and R3 are within the OSPF backbone area. The ISP router is used as the gateway to the internet of the routing domain.
Router Configuration Mode for OSPF
The OSPFv2 is able to use the router ospf process-id global configuration mode, the value chose a number is selected by the network, Then the process-id is loclay significant, this means that is doesn´t need to be the same value on the other OSPF router to stabilish the adjacencies with those neighbors
Router ID's
An OSPF router ID is a 32-bit value, represented as an IPv4 address. This ID is unique as an identifier for the OSPF, all the OFPS Packets contain the originating router. Every router needs an ID to participate in the domain.
Router ID of Precedence
But how does the router determine the router ID? As illustrated in the figure, Cisco routers derive the router ID based on one of three criteria, in the following preferential order:
Configure a Loopback Interfaces as the Router ID
The loopback interfaces have not been configured. When OSPF routing is enabled on the router, the routers would pick the following highest active configured IPv4 address as the router ID.
Explicitly Configure a Router ID
In the figure, the topology has been updated to show the router ID for each router:
Modify a Router ID
After a router selects a router ID, an active OSPF router does not allow the router ID to be changed until the router is reloaded or the OSPF process is reset.
Syntax Checker - Configure R2 and R3 Router IDs
Multiaccess OSPF Networks
2.3.1 OSPF Network Types
Another type of network that uses OSPF is the multiaccess OSPF network. Multiaccess OSPF networks are unique in that one router controls the distribution of LSAs. The router that is elected for this role should be determined by the network administrator through proper configuration.
2.3.7 DR Failure and Recovery
After the DR is elected, it remains the DR Unitl one of the following events occurs:
The DR fails.
The OSPF process on the DR fails or is stopped.
The multiaccess interface on the DR fails or is shutdown.
2.3.8 The IP ospf priority Command
If the interface priorities are equal an all routers, the router with the highest router ID is elected the DR.
This process only works if there ur a stringent paln for setting the router.
Instead of relyign on the router ID, it is better to control the election by setting interface priorities.
2.3.9 Configure OSPF Priority
In the topology, the ip ospf priority command will be used to change the DR and BDR as follows:
R1 should be the DR and will be configured with a priority of 255
.
2.R2 should be the BDR and will be left with the default priority of 1.
3.R3 should never be a DR or BDR and will be configured with a priority of 0.
I2.3.2 OSPF Designated Router
In multiaccess networks, OSPF elects a DR and BDR as a solution to manage the number of adjacencies and the flooding of link-state advertisements (LSAs). The DR is responsible for collecting and distributing LSAs sent and received. The DR uses the multicast IPv4 address 224.0.0.5 which is meant for all OSPF routers.
2.3.3 OSPF Multiaccess Reference Topology
Because the routers are connected over a common multiaccess network, OSPF has automatically elected a DR and BDR. In this example, R3 has been elected as the DR because its router ID is 3.3.3.3, which is the highest in this network. R2 is the BDR because it has the second highest router ID in the network.
2.3.4 Verificar las funciones del router OSPF
2.3.5 Verify DR/BDR Adjacencies
FULL/DR - The router is fully adjacent with the indicated DR neighbor. These two neighbors can exchange Hello packets, updates, queries, replies, and acknowledgments.
FULL/BDR - The router is fully adjacent with the indicated BDR neighbor. These two neighbors can exchange Hello packets, updates, queries, replies, and acknowledgments.
FULL/DROTHER - This is a DR or BDR router that is fully adjacent with a non-DR or BDR router. These two neighbors can exchange Hello packets, updates, queries, replies, and acknowledgments.
2-WAY/DROTHER - The non-DR or BDR router has a neighbor relationship with another non-DR or BDR router. These two neighbors exchange Hello packets.
2.3.6 Default DR/BDR Election Process
The DR and BDR election process takes place as soon as the first router with an OSPF-enabled interface is active on the multiaccess network. This can happen when the preconfigured OSPF routers are powered on, or when OSPF is activated on the interface. The election process only takes a few seconds. If all of the routers on the multiaccess network have not finished booting, it is possible that a router with a lower router ID becomes the DR.
2.5.1 Propagate a Default Static Route in OSPFv2
Your network users will need to send packets out of your network to non-OSPF networks, such as the internet.
You can verify the default route settings on R2 using the show ip route command. You can also verify that R1 and R3 received a default route.
R2 Routing Table
:
R1 Routing table
R3 Routing Table
2.5.2 Verify the Propagated Default Route
2.6 Verify Single-Area OSPFv2
2.6.1 Verify OSPF Neighbors
If you have configured single-area OSPFv2, you will need to verify your configurations. This topic details the many commands that you can use to verify OSPF.
As you know, the following two commands are particularly useful for verifying routing:
show ip interface brief - This verifies that the desired interfaces are active with correct IP addressing.
show ip route- This verifies that the routing table contains all the expected routes.
2.6.2 Verify OSPF Protocol Settings
The show ip protocols command is a quick way to verify vital OSPF configuration information, as shown in the following command output.
2.6.3 Verify OSPF Process Information
The show ip ospf command can also be used to examine the OSPFv2 process ID and router ID, as shown in the following command output. This command displays the OSPFv2 area information and the last time the SPF algorithm was executed.
2.6.4 Verify OSPF Interface Settings
The show ip ospf interface command provides a detailed list for every OSPFv2-enabled interface. This command shows the process ID, the local router ID, the type of network, OSPF cost, DR and BDR information on multiaccess links (not shown), and adjacent neighbors.
2.4 Modify Single-Area OSPFv2
2.4.1 Cisco OSPF Cost Metric
2.4.7 Hello Packet Intervals
The Dead interval is the period that the router waits to receive a Hello packet before declaring the neighbor down. If the Dead interval expires before the routers receive a Hello packet, OSPF removes that neighbor from its link-state database (LSDB). The router floods the LSDB with information about the down neighbor out all OSPF-enabled interfaces. Cisco uses a default of 4 times the Hello interval. This is 40 seconds on multiaccess and point-to-point networks.
2.4.8 Verify Hello and Dead Intervals
The OSPF Hello and Dead intervals are configurable on a per-interface basis. The OSPF intervals must match or a neighbor adjacency does not occur. To verify the currently configured OSPFv2 interface intervals, use the show ip ospf interface command, as shown in the example. The Gigabit Ethernet 0/0/0 Hello and Dead intervals are set to the default 10 seconds and 40 seconds respectively.
Pointto-Point OSPF Networks
The Network Comand Syntax
