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CCNP ENCOR Certification Cram Notes : Infrastructure

3.2 Layer 3

3.2.a Compare routing concepts of EIGRP and OSPF (advanced distance vector vs. linked state, load balancing, path selection, path operations, metrics)

EIGRP (Enhanced Interior Gateway Routing Protocol) and OSPF (Open Shortest Path First) are two popular routing protocols used in enterprise networks. Both protocols have their own advantages and disadvantages, and network administrators need to consider several factors before selecting one over the other.

Here are some comparisons between the routing concepts of EIGRP and OSPF:

1. Distance Vector vs. Link State: EIGRP is an advanced distance vector protocol, while OSPF is a link-state protocol. EIGRP uses distance vector algorithms to calculate the best path to a destination, while OSPF uses link-state algorithms.

2. Load Balancing: EIGRP supports unequal-cost load balancing, which allows for better utilization of network resources by allowing traffic to be sent across different paths with different metrics. OSPF also supports load balancing, but only for equal-cost paths.

3. Path Selection: Both EIGRP and OSPF use metrics to determine the best path to a destination. EIGRP uses bandwidth, delay, reliability, load, and MTU as metrics, while OSPF uses cost as the primary metric.

4. Path Operations: EIGRP uses the Diffusing Update Algorithm (DUAL) to calculate the best path to a destination. OSPF uses the Shortest Path First (SPF) algorithm to calculate the best path.

5. Convergence: EIGRP converges faster than OSPF due to its efficient use of bandwidth and rapid path recalculation.

3.2.b Configure and verify simple OSPF environments, including multiple normal areas, summarization, and filtering (neighbor adjacency, point-to-point and broadcast network types, and passive interface)

OSPF (Open Shortest Path First) is a link-state routing protocol used to advertise routes between routers in a network. OSPF has several features that make it a popular choice for enterprise networks, including fast convergence times, support for multiple paths, and scalable network design. In this section, we will discuss how to configure and verify simple OSPF environments, including multiple normal areas, summarization, and filtering.

1. OSPF Area Configuration: OSPF divides the network into logical areas to minimize the number of LSAs (Link State Advertisements) that are transmitted across the network. To configure OSPF areas, follow these steps:

  • Enable OSPF on the router using the "router ospf" command.

  • Configure the router ID using the "router-id" command.

  • Configure the network types using the "network" command. OSPF supports point-to-point, broadcast, and non-broadcast networks.

  • Assign interfaces to specific OSPF areas using the "area" command.

2. OSPF Summarization: OSPF summarization is used to reduce the size of the routing table by advertising a single summary route instead of multiple individual routes. To configure OSPF summarization, follow these steps:

  • Enable OSPF summarization using the "area range" command.

  • Specify the IP address range to summarize.

  • Specify the summary route using the "summary-address" command.

3. OSPF Filtering: OSPF filtering is used to prevent specific routes from being advertised across the network. To configure OSPF filtering, follow these steps:

  • Enable OSPF filtering using the "distribute-list" command.

  • Create an access list to specify the routes to filter.

  • Apply the access list to incoming or outgoing OSPF routes using the "in" or "out" keyword.

4. OSPF Verification: To verify OSPF configurations, use the following commands:

  • "show ip ospf neighbor": Displays the neighbor OSPF routers.

  • "show ip ospf database": Displays the OSPF database.

  • "show ip route": Displays the routing table.

  • "show ip ospf interface": Displays OSPF interface configuration and status.

In summary, OSPF is a robust routing protocol that provides several features to optimize network design. By properly configuring OSPF areas, summarization, and filtering, network administrators can create efficient and scalable networks.

3.2.c Configure and verify eBGP between directly connected neighbors (best path selection algorithm and neighbor relationships)

eBGP (external Border Gateway Protocol) is a routing protocol used for exchanging routing information between different autonomous systems (AS). Here are the steps to configure and verify eBGP between directly connected neighbors:

1. Configure IP addresses on the interfaces: Configure IP addresses on the interfaces that connect the BGP routers. Ensure that the interfaces are up and the IP addresses are reachable.

2. Enable BGP: Enable BGP on the routers using the router bgp command. Configure the AS number for the local router.

3. Configure neighbor statements: Configure the neighbor statements using the neighbor command. Specify the IP address of the neighbor, its AS number, and the remote AS number.

4. Configure network statements: Configure network statements using the network command. Specify the IP address and the subnet mask of the network.

5. Verify eBGP neighbor relationships: Use the show ip bgp summary command to verify eBGP neighbor relationships. Ensure that the neighbor IP addresses are listed, the state is "Established," and the local AS number and the remote AS number match.

6. Verify the BGP table: Use the show ip bgp command to verify the BGP table. Ensure that the networks are listed with their next hop IP address.

7. Verify best path selection: Use the show ip bgp command to verify the best path selection algorithm. Ensure that the selected path has the lowest value for the BGP attributes.

8. Verify BGP filters: Use the show ip bgp command to verify BGP filters. Ensure that the networks that are not allowed are not listed in the BGP table.

By following these steps, you can configure and verify eBGP between directly connected neighbors.


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