OSPF Routing Protocol (IPv4 Networks)

Questions and Answers

What type of routing protocol is OSPF?

Hybrid routing protocol

Distance vector routing protocol

Path vector routing protocol

Link state routing protocol (correct)

What is the purpose of the advertisements sent by OSPF speakers?

To request routing updates from other routers

To negotiate with other routers for the shortest path

To provide link state information to other OSPF speakers (correct)

To advertise the OSPF version number

What layer of the OSI model does OSPF operate at?

Layer 5

Layer 3 (correct)

Layer 2

Layer 4

What multicast address does OSPF typically use for sending advertisements?

224.0.0.5 Signup and view all the answers

What is the primary goal of OSPF when building its routing table?

To choose the shortest path to the destination Signup and view all the answers

What is the main difference between OSPF and RIP?

OSPF is a link state protocol, while RIP is a distance vector protocol Signup and view all the answers

What type of networks does OSPF support?

Only IPv4 networks Signup and view all the answers

What happens when multiple OSPF speakers send advertisements?

Each router receives advertisements from all other OSPF speakers Signup and view all the answers

Which protocol has a better administrative distance than RIP?

OSPF Signup and view all the answers

What is the multicast address associated with OSPF?

224.0.0.10 Signup and view all the answers

What is the protocol number for OSPF in the IP header?

89 Signup and view all the answers

What is the OSPF version that supports IP version 4?

OSPF Version 2 Signup and view all the answers

What is the purpose of the 'debug IP routing' command?

To display the current routing table Signup and view all the answers

What is the administrative distance of RIP?

120 Signup and view all the answers

What is the purpose of the 'show IP route' command?

To display the current routing table Signup and view all the answers

What is the meaning of 'neighbor adjacency' in the context of OSPF?

A connection between two routers that are running OSPF Signup and view all the answers

What is the purpose of the 'capture' feature in the context of the content?

To capture network traffic Signup and view all the answers

What is the purpose of the 'flush' command in the context of the content?

To remove a specific route from the routing table Signup and view all the answers

What is the layer 4 protocol number for OSPF?

89 Signup and view all the answers

What is the administrative distance (AD) of a static route?

1 Signup and view all the answers

What is the administrative distance (AD) of OSPF by default?

110 Signup and view all the answers

Which protocol has a layer 4 protocol number of 50?

IPsec Signup and view all the answers

When two different routing protocols learn about the same network, how does a router decide which route to use?

The protocol with the lowest administrative distance is chosen. Signup and view all the answers

What is the administrative distance (AD) of RIP?

120 Signup and view all the answers

If a router learns about the same network through both RIP and OSPF, which protocol's route will be placed in the routing table?

The OSPF route will be used because it has a lower administrative distance. Signup and view all the answers

What is the significance of the administrative distance (AD) in routing protocols?

It determines the priority of a route learned by a specific protocol. Signup and view all the answers

What is the significance of protocol numbers at layer 4?

They allow devices to distinguish between different layer 4 protocols. Signup and view all the answers

What is the purpose of specifying an ID number when configuring OSPF on a router?

To provide a unique identifier for the OSPF process on the router. Signup and view all the answers

Study Notes

OSPF (Open Shortest Path First)

OSPF is a link-state routing protocol that supports IPv4 networks
Each device running OSPF (OSPF speaker) sends advertisements containing link details and state
These advertisements are forwarded to other devices, allowing each device to build a map of the network and determine the fastest path for forwarding packets

Characteristics of OSPF

At layer 3, OSPF uses a multicast address of 224.0.0.5 (sometimes 224.0.0.6) for updates
At layer 4, OSPF has its own protocol number, 89, which is different from TCP (6), UDP (17), and other protocols

Administrative Distance

When a router learns about the same network via multiple routing protocols, it uses administrative distance (AD) to choose the best route
AD is used to decide which route to put into the routing table
The route with the lowest AD is chosen
The AD values are:
- Static route: 1
- OSPF: 110
- RIP: 120

OSPF in Action

In the demonstration, OSPF is configured on the routers, and they start to learn about the network via OSPF
The OSPF-learned routes replace the RIP-learned routes due to OSPF's lower administrative distance
The routers form neighbor adjacencies and exchange advertisements, allowing them to build a map of the network

Capturing OSPF Traffic

In the packet capture, OSPF traffic is captured, showing the multicast address and protocol number 89
The OSPF payload contains the advertised routes and other information
OSPF version 2 is used, which supports IPv4 networks, while OSPF version 3 supports IPv6 networks