Supporting BCVRE Study Guide Chapter 10 OSPF Single-Area

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Supporting BCVRE Study Guide Chapter 10 OSPF Single-Area
Supporting BCVRE Study Guide Chapter 10 OSPF Single-Area

Objectives: As a Brocade Certified vRouter Engineer, you must be able to demonstrate the ability to install, configure and troubleshoot features of Brocade Vyatta Network OS.

Target: This course is for anyone tasked with configuring or managing the Brocade Vyatta vRouter. This course also for those who are preparing to take the BCVRE Certification Exam.

Bacaan Lainnya

Course prerequisites: Before taking these bundled courses, students should have basic IT networking experience, including working knowledge of TCP/IP.

BCvRE Bootcamp

Agenda:

  • Open Shortest Path First
  • Configuring OSPF
  • Verifying OSPF Operations

Open Shortest Path First

Open Shortest Path First (OSPF) is a link state routing Interior Gateway Protocol (IGP) for medium to large networks.

Its cost metric is based on aggregated link cost.

OSPF supports Classless Inter-Domain Routing (CIDR) and Variable Length Subnet Masks (VLSM).

It is hierarchy-based using OSPF areas.

Its network topology is built using Link State Advertisements (LSAs) received from other routers.

OSPF has the following characteristics:

  • Decreases routing overhead.
  • Speeds up convergence.
  • Confines network instability to a single area of the network.
  • Communicates between routers using multicast advertisements.
  • Has no periodic updates.
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Designated Router (DR)

OSPF has a Designated Router which receives all the updates on a given segment.

The Backup Designated Router is the second-incommand.

This router receives the updates, too, but does not send them back out.

When a router needs to update other routers, it sends the update to the Designated Router and the Backup Designated Router.

The Designated Router sends the update to all of the other routers on its segment.

When the Designated Router becomes unavailable, the Backup Designated Router instantly becomes the Designated Router, and an election is held to see who becomes the next Backup Designated Router.

This way, each router need not be aware of all of the OSPF routers involved. It needs only to communicate updates (and receive updates) from a single source.

  • This minimizes traffic, and allows the OSPF design to expand nicely, as needed

OSPF DR Election

Designated Router (DR) election is done by selecting the neighboring router with the highest priority.

The router with the next largest priority is elected as the Backup DR (BDR).

If the DR goes offline, the BDR automatically becomes the DR.

  • The router with the next highest priority becomes the new BDR

If two neighbors share the same priority, the router with the highest router ID is designated as the DR.

Router ID:

  • The Router ID can be manually configured using the global ip router-id x.x.x.x command.
  • If the Router ID is not manually configured, the IP address configured on the lowest numbered loopback interface is used as the Router ID.
  • If there is no loopback interface, then the router ID is the lowest numbered IP address configured on the device.
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The DR and BDR election process is performed when one of the following events occurs:

  • An interface is in a waiting state and the wait time expires.
  • An interface is in a waiting state and a hello packet is received that addresses the BDR.
  • A change in the neighbor state occurs, such as, a neighbor state transitions from 2 or higher, communication to a neighbor is lost, or a neighbor declares itself to be the DR or BDR for the first time
OSPF DR Election
OSPF DR Election

OSPF Neighbor Adjacency

OSPF defines a neighbor as a router that has an interface with an IP address in the same broadcast domain.

The following parameters must match to become neighbors:

  • Subnet mask
  • Hello/Dead intervals
  • Area-ID
  • Authentication password
  • Stub area flag

OSPF Neighbor States

The neighbors on a given router will go through six states on their way to fully becoming synchronized with its routing table.

The first three states are referred to as the neighboring process.

  • Down: The router has not sent a Hello packet, nor has it received one.
  • Init: A Hello packet has been sent to a neighbor, but no Hello packet has been received from that neighbor.
  • 2 Way: The router has sent a Hello packet to a neighbor, and has received a Hello packet back; the reply will contain your router’s Router ID inside; now, your router knows that the neighbor knows your router as well.

The next three states are referred to as the adjacency process. To establish adjacency means that your OSPF database is synchronized with your
neighbor.

  • Ex-Start: This is short for “Exchange Start”; this is where the DR/BDR election takes place; routers sending Hello packets to determine who will become the DR and BDR.
  • Exchange: Now the neighbors are finally talking; in this state, your router is sharing everything it knows, and the neighbor router is sharing everything it knows.
  • Full: We are adjacent! The neighbors have no more information to share; they’ve shared it all
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Areas

  • Routers in OSPF are split into different groups called areas.
  • The purpose is to reduce traffic and CPU load.
  • The area that is the most restrictive uses the least resources (CPU and memory).
  • Areas may be organized in any way that makes the most sense for a particular network.
  • Areas are assigned numbers on the range of 1 through 4,294,967,295.
Areas
Areas

Configuring OSPF

Sample Topology

Sample Topology
Sample Topology

R1 OSPF Configuration

R2 OSPF Configuration

R3 OSPF Configuration

Verifying OSPF Operations

R1 OSPF Verification

R2 OSPF Verification

R3 OSPF Verification

The End of The Word

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